Spectrophotometric Assays for Measuring Photorespiratory Glutamate:Glyoxylate and Serine:Glyoxylate Aminotransferase Reactions.

Glutamate:glyoxylate aminotransferase (GGAT; EC 2.6.1.4) and serine:glyoxylate aminotransferase activities (SGAT; EC 2.6.1.45) are central photorespiratory reactions within plant peroxisomes. Both enzymatic reactions convert glyoxylate, a product of glycolate oxidase, to glycine, a substrate of the mitochondrial glycine decarboxylase complex. The GGAT reaction uses glutamate as an amino group donor and also produces α-ketoglutarate, which is recycled to glutamate in plastids by ferredoxin-dependent glutamate synthase. Using serine, a product of mitochondrial serine hydroxymethyltransferase, as an amino group donor, the SGAT reaction also produces hydroxypyruvate, a substrate of hydroxypyruvate reductase. The activities of these photorespiratory aminotransferases can be measured using indirect, coupled, spectrophotometric assays, detailed herein.

Spectrophotometric Assays for Measuring Hydroxypyruvate Reductase Activity.

Hydroxypyruvate reductase (HPR; EC 1.1.1.81) activity is integral to the photorespiratory pathway. Within photorespiration, HPR catalyzes the reduction of hydroxypyruvate, a product of the serine:glyoxylate aminotransferase reaction to glycerate, a substrate for glycerate kinase, using NADH as cofactor. Here we detail a spectrophotometric assay for measuring HPR activity in vitro by following the consumption of NADH at 340 nm.

Multi-Method Quantification of Acetyl-Coenzyme A and Further Acyl-Coenzyme A Species in Normal and Ischemic Rat Liver.

Thioesters of coenzyme A (CoA) carrying different acyl chains (acyl-CoAs) are central intermediates of many metabolic pathways and donor molecules for protein lysine acylation. Acyl-CoA species largely differ in terms of cellular concentrations and physico-chemical properties, rendering their analysis challenging. Here, we compare several approaches to quantify cellular acyl-CoA concentrations in normal and ischemic rat liver, using HPLC and LC-MS/MS for multi-acyl-CoA analysis, as well as NMR, fluorimetric and spectrophotometric techniques for the quantification of acetyl-CoAs. In particular, we describe a simple LC-MS/MS protocol that is suitable for the relative quantification of short and medium-chain acyl-CoA species. We show that ischemia induces specific changes in the short-chain acyl-CoA relative concentrations, while mild ischemia (1-2 min), although reducing succinyl-CoA, has little effects on acetyl-CoA, and even increases some acyl-CoA species upstream of the tricarboxylic acid cycle. In contrast, advanced ischemia (5-6 min) also reduces acetyl-CoA levels. Our approach provides the keys to accessing the acyl-CoA metabolome for a more in-depth analysis of metabolism, protein acylation and epigenetics.

Charge Transfer Complex of Lorlatinib with Chloranilic Acid: Characterization and Application to the Development of a Novel 96-Microwell Spectrophotometric Assay with High Throughput.

Lorlatinib (LRL) is the first drug of the third generation of anaplastic lymphoma kinase (ALK) inhibitors used a first-line treatment of non-small cell lung cancer (NSCLC). This study describes, for the first time, the investigations for the formation of a charge transfer complex (CTC) between LRL, as electron donor, with chloranilic acid (CLA), as a π-electron acceptor. The CTC was characterized by ultraviolet (UV)-visible spectrophotometry and computational calculations. The UV-visible spectrophotometry ascertained the formation of the CTC in methanol via formation of a new broad absorption band with maximum absorption peak (λmax) at 530 nm. The molar absorptivity (ε) of the complex was 0.55 × 103 L mol-1 cm-1 and its band gap energy was 2.3465 eV. The stoichiometric ratio of LRL/CLA was found to be 1:2. The association constant of the complex was 0.40 × 103 L mol-1, and its standard free energy was -0.15 × 102 J mole-1. The computational calculation for the atomic charges of an energy minimized LRL molecule was conducted, the sites of interaction on the LRL molecule were assigned, and the mechanism of the reaction was postulated. The reaction was adopted as a basis for developing a novel 96-microwell spectrophotometric method (MW-SPA) for LRL. The assay limits of detection and quantitation were 2.1 and 6.5 µg/well, respectively. The assay was validated, and all validation parameters were acceptable. The assay was implemented successfully with great precision and accuracy to the determination of LRL in its bulk form and pharmaceutical formulation (tablets). This assay is simple, economic, and more importantly has a high-throughput property. Therefore, the assay can be valuable for routine in quality control laboratories for analysis of LRL's bulk form and pharmaceutical tablets.

Development of Green and High Throughput Microplate Reader-Assisted Universal Microwell Spectrophotometric Assay for Direct Determination of Tyrosine Kinase Inhibitors in Their Pharmaceutical Formulations Irrespective the Diversity of Their Chemical Structures.

This study discusses the development and validation of a universal microwell spectrophotometric assay for TKIs, regardless of the diversity in their chemical structures. The assay depends on directly measuring the native ultraviolet light (UV) absorption of TKIs. The assay was carried out using UV-transparent 96-microwell plates and the absorbance signals were measured by a microplate reader at 230 nm, at which all TKIs had light absorption. Beer's law correlating the absorbances of TKIs with their corresponding concentrations was obeyed in the range of 2-160 µg mL-1 with excellent correlation coefficients (0.9991-0.9997). The limits of detection and limits quantitation were in the ranges of 0.56-5.21 and 1.69-15.78 µg mL-1, respectively. The proposed assay showed high precision as the values of the relative standard deviations for the intra- and inter-assay precisions did not exceed 2.03 and 2.14%, respectively. The accuracy of the assay was proven as the recovery values were in the range of 97.8-102.9% (±0.8-2.4%). The proposed assay was successfully applied to the quantitation of all TKIs in their pharmaceutical formulations (tablets) with reliable results in terms of high accuracy and precision. The assay greenness was evaluated, and the results proved that the assay fulfils the requirements of green analytical approach. The proposed assay is the first assay that can analyse all TKIs on a single assay system without chemical derivatization or modifications in the detection wavelength. In addition, the simple and simultaneous handling of a large number of samples as a batch using micro-volumes of samples gave the assay the advantage of high throughput analysis, which is a serious demand in the pharmaceutical industry.

Spectrophotometric Investigations of Charge Transfer Complexes of Tyrosine Kinase Inhibitors with Iodine as a σ-Electron Acceptor: Application to Development of Universal High-Throughput Microwell Assay for Their Determination in Pharmaceutical Formulations.

Background and Objective: Tyrosine kinase inhibitors (TKIs) are used for the treatment of different types of cancers. The current study describes, for the first time, the ultraviolet-visible spectrophotometric investigation of charge transfer complexes (CTCs) of seven TKIs, as electron donors, and iodine, as σ-electron. Materials and Methods: The formation of CTCs was promoted in dichloromethane, among the other solvents used in the investigation. The molar absorptivity values, association constants, and free energy changes of the CTCs were determined. Stoichiometric ratio of TKI: iodine as well as TKIs site(s) of interaction were addressed. Reaction was the basis for constructing a novel simple and accurate 96-microwell spectrophotometric assay (MW-SPA) with high-throughput property for the quantitative determination of TKIs in their pharmaceutical formulations. Results: Beer's law, which relates CTC absorbances to TKI concentrations, was followed within the optimal range of 2 to 100 µg/well (r ranged from 0.9991 to 0.9998). Detection and quantification limits ranged from 0.91 to 3.60 and 2.76 to 10.92 g µmL-1, respectively. Relative standard deviations values for the intra- and inter-assay precisions of the proposed MW-SPA did not exceed 2.13 and 2.34%, respectively. Studies of recovery demonstrated MW-SPA accuracy, with results ranging from 98.9% to 102.4%. All TKIs, both in bulk form and in pharmaceutical formulations (tablets), were effectively determined using the suggested MW-SPA. Conclusions: The current MW-SPA involved a simple procedure and it was convenient as it could analyse all proposed TKIs utilizing a single assay system at once measuring wavelengths for all TKIs. In addition, the proposed MW-SPA has high throughput which enables the processing of a batch of huge samples' number in very short reasonable time period. In conclusion, TKIs can be routinely analysed in their dosage forms in quality control laboratories, and the assay can be highly valuable and helpful in this regard.

Spectrophotometric Method for the Quantification and Kinetic Evaluation of In Vitro c-di-GMP Hydrolysis in the Presence and Absence of Oxygen.

A spectrophotometric method to measure hydrolysis of the bacterial second messenger cyclic dimeric guanosine monophosphate is described for characterization of enzymes under aerobic and anaerobic conditions. The method allows for obtaining all necessary data to calculate KM and kcat from reactions within a single 96-well plate that can be measured using a standard plate reader. The spectrophotometric assay has been used to measure the rates and obtain Michaelis-Menten parameters for the c-di-GMP phosphodiesterase DcpG with the sensor domain in various ligation states.

A Spectrophotometric Turbidity Assay to Study Liquid-Liquid Phase Separation of UBQLN2 In Vitro.

Liquid-liquid phase separation (LLPS) is hypothesized to be the underlying mechanism for how membraneless organelles or biomolecular condensates form inside both prokaryotic and eukaryotic cells. Protein LLPS is a biophysical process during which proteins demix from homogeneous solution to form protein-dense droplets with liquid-like properties. Disruptions to LLPS, such as changes to material properties of condensates or physicochemical parameters for LLPS onset, are implicated in neurodegenerative diseases and cancer. Therefore, it is essential to determine the physicochemical parameters that promote protein LLPS. Here, we present our UV-Vis spectrophotometric turbidity assay to characterize the temperature and concentration dependence of LLPS for UBQLN2, a protein that undergoes LLPS via homotypic interactions in vitro and forms stress-induced condensates in cells. Mutations in UBQLN2 cause amyotrophic lateral sclerosis (ALS) and disrupt UBQLN2 LLPS. We present a detailed expression and purification protocol for a C-terminal construct of UBQLN2 and how we use microscopy to image UBQLN2 LLPS. We use our UV-Vis assay to construct temperature-concentration phase diagrams for wild-type and mutant UBQLN2 constructs to determine the effects of domain deletions and/or mutations on UBQLN2 phase separation.

Visible spectrophotometric assay for characterization of ω-transaminases.

Omega-transaminases (ω-TAs) have attracted considerable interest for their use in asymmetric synthesis of chiral amines with a high degree of optical purity and yield. The rapid evaluation of the characteristics of newly identified or engineered ω-TAs is important for industrial applications. In this study, a visible spectrophotometric assay was developed for rapid quantitative determination of ω-TA activities based on the transamination of 2-(4-nitrophenyl)ethan-1-amine to generate a red product (E)-N-(4-nitrophenethyl)-2-(4-nitrophenyl)ethen-1-amine. After various co-solvents were evaluated, dimethyl sulfoxide (DMSO) was considered optimal because the red product exhibits good solubility and retains its original color. The red product dissolved in DMSO has its highest absorbance at 465 nm, and its concentration has a good linear relationship with the absorbance. A spectrophotometric assay was established and validated using conventional HPLC analysis (<10% divergence). This method was then used to characterize an ω-TA from thermophilic Geobacillus thermoleovorans and an ω-TA obtained from the metagenome of a soda lake. The results demonstrated that ω-transaminase enzymatic properties could be characterized simply, rapidly, and at low cost, using this newly established visible spectrophotometric assay method.

Continuous Spectrophotometric Assay for High-Throughput Screening of Predominant d-Allulose 3-Epimerases.

d-Allulose is an attractive noncaloric sugar substitute with numerous health benefits, which can be biosynthesized by d-allulose 3-epimerases (DAEases). However, enzyme instability under harsh industrial reaction conditions hampered its practical applications. Here, we developed a continuous spectrophotometric assay (CSA) for the efficient analysis of d-allulose in a mixture. Furthermore, a high-throughput screening strategy for DAEases was developed using CSA by coupling DAEase with a NADH-dependent ribitol dehydrogenase, enabling high-throughput screening of DAEase variants with desired properties. The variant M15S/P40N/S209N exhibited a half-life of 22 h at 60 °C and an 8.7 °C increase of the T5060 value, with a 1.2-fold increase of activity. Structural modeling and molecular dynamics simulations indicated that the improvement of thermostability and activity was due to some new hydrogen bonds between chains at the dimer interface and between the residue and the substrate d-fructose. This work offers a robust tool and theoretical basis for the improvement of DAEases, which will benefit the enzymatic biosynthesis of d-allulose and promote its industrial application.

Intra-Laboratory Validation of Alpha-Galactosidase Activity Measurement in Dietary Supplements.

INTRODUCTION: Alpha-galactosidase (α-Gal) is an enzyme responsible for the hydrolyzation of glycolipids and glycoprotein commonly found in dietary sources. More than 20% of the general population suffers from abdominal pain or discomfort caused by intestinal gas and by indigested or partially digested food residuals. Therefore, α-Gal is used in dietary supplements to reduce intestinal gases and help complex food digestion. Marketed enzyme-containing dietary supplements must be produced in accordance with the Food and Drug Administration (FDA) regulations for Current Good Manufacturing Practice (cGMPs). AIM: in this work we illustrated the process used to develop and validate a spectrophotometric enzymatic assay for α-Gal activity quantification in dietary supplements. METHODS: The validation workflow included an initial statistical-phase optimization of materials, reagents, and conditions, and subsequently a comparative study with another fluorimetric assay. A final validation of method performance in terms of specificity, linearity, accuracy, intermediate-precision repeatability, and system precision was then executed. RESULTS AND CONCLUSIONS: The proven method achieved good performance in the quantitative determination of α-Gal activity in commercial food supplements in accordance with the International Council for Harmonisation of Technical Requirements for Pharmaceuticals (ICH) guidelines and is suitable as a rapid in-house quality control test.

Kinetics of glucosinolate hydrolysis by myrosinase in Brassicaceae tissues: A high-performance liquid chromatography approach.

Glucosinolates are a group of secondary metabolites occurring in all the vegetables belonging to the Brassicaceae family. Upon tissue damage, glucosinolates are hydrolyzed by myrosinase to a series of degradation products, including isothiocyanates, which are important for their health-promoting effects in humans. The glucosinolate-myrosinase system has been characterized in several Brassica species, of which white mustard (Sinapis alba) has been studied the most. In this study, a new HPLC-UV assay to evaluate the activities and kinetics of myrosinases in aqueous extracts, which closely represent the physiological conditions of plant tissues, was developed. This method was tested on myrosinases extracted from broccoli and cauliflower inflorescences, employing sinigrin and glucoraphanin as substrates. The results showed a strong inhibition of both enzymes at high substrate concentrations. The main issues related to kinetic analysis on the glucosinolate-myrosinase system were also elucidated.

Charge-Transfer Complex of Linifanib with 2,3-dichloro-3,5-dicyano-1,4-benzoquinone: Synthesis, Spectroscopic Characterization, Computational Molecular Modelling and Application in the Development of Novel 96-microwell Spectrophotometric Assay.

BACKGROUND: Linifanib (LFB) is a multi-targeted receptor tyrosine kinase inhibitor used in the treatment of hepatocellular carcinoma and other types of cancer. The charge-transfer (CT) interaction of LFB is important in studying its receptor binding mechanisms and useful in the development of a reliable CT-based spectrophotometric assay for LFB in its pharmaceutical formulation to assure its therapeutic benefits. PURPOSE: The aim of this study was to investigate the CT reaction of LFB with 2,3-dichloro-3,5-dicyano-1,4-benzoquinone (DDQ) and its application in the development of a novel 96-microwell spectrophotometric assay for LFB. METHODS: The reaction was investigated, its conditions were optimized, the physicochemical and constants of the CT complex and stoichiometric ratio of the complex were determined. The solid-state LFB-DDQ complex was synthesized and its structure was analyzed by UV-visible, FT-IR, and 1H-NMR spectroscopic techniques, and also by the computational molecular modeling. The reaction was employed in the development of a novel 96-microwell spectrophotometric assay for LFB. RESULTS: The reaction resulted in the formation of a red-colored product, and the spectrophotometric investigations confirmed that the reaction had a CT nature. The molar absorptivity of the complex was linearly correlated with the dielectric constant and polarity index of the solvent; the correlation coefficients were 0.9526 and 0.9459, respectively. The stoichiometric ratio of LFB:DDQ was 1:2. The spectroscopic and computational data confirmed the sites of interaction on the LFB molecule, and accordingly, the reaction mechanism was postulated. The reaction was utilized in the development of the first 96-microwell spectrophotometric assay for LFB. The assay limits of detection and quantitation were 1.31 and 3.96 µg/well, respectively. The assay was successfully applied to the analysis of LFB in its bulk and tablets with high accuracy and precision. CONCLUSION: The assay is simple, rapid, accurate, eco-friendly as it consumes low volumes of organic solvent, and has high analysis throughput.

Spectrophotometric and computational investigations of charge transfer complexes of chloranilic acid with tyrosine kinase inhibitors and application to development of novel universal 96-microwell assay for their determination in pharmaceutical formulations.

The tyrosine kinase inhibitors (TKIs) are chemotherapeutic drugs used for targeted therapy of various types of cancer. In literature, there is no existing universal chromogenic reagent used for development of spectrophotometric assay for all TKIs regardless the diversity of their chemical structures. This work discusses, for the first time, the experimental and computational evaluation of chloranilic acid (CLA) as a universal chromogenic reagent for developing a novel 96-microwell spectrophotometric assay (MW-SPA) for TKIs. The reaction of CLA with seven TKIs was examined in different organic solvents of various dielectric constants and polarity indexes. The reaction resulted in an instantaneous formation of intensely purple coloured products with all the investigated TKIs. Spectrophotometric investigations confirmed that the reactions proceeded via the formation of charge-transfer complexes (CTC). The physical parameters (molar absorptivity, molar ratio, association constant and standard free energy) were determined for the CTC of all TKIs. Computational calculations for the relative electron densities on each atom of the TKI molecule and molecular modelling for the CTC were conducted, and the site(s) of interaction on each TKI molecule were determined. Under the optimized conditions, Beer's law correlating the absorbances of the CTC with the concentrations of TKIs were obeyed in the range of 5-500 µg/well with good correlation coefficients (0.9991-0.9998). The limits of detection and quantitation were in the ranges of 1.89-5.09 and 5.74-15.42 µg/well, respectively. The proposed MW-SPA showed high precisions as the values of the relative standard deviations did not exceed 2.01 and 2.45% for the intra- and inter-assay precision, respectively. The accuracy of MW-SPA was proved by recovery studies as the recovery values were in the range of 98.8-103.7%. The proposed MW-SPA was successfully applied for the determination of all TKIs in their bulk forms and pharmaceutical formulations (tablets) with good accuracy and precisions. The proposed MW-SPA is the first assay that can analyse all the TKIs on a single assay system without modifications in the detection wavelength. Additional advantages of the proposed MW-SPA are simple, economic, and more importantly have high throughput. Therefore, the assay can be helpful and beneficial for routine analysis of TKIs in their pharmaceutical formulations in quality control laboratories.

Experimental and Computational Evaluation of Chloranilic Acid as an Universal Chromogenic Reagent for the Development of a Novel 96-Microwell Spectrophotometric Assay for Tyrosine Kinase Inhibitors.

The tyrosine kinase inhibitors (TKIs) are chemotherapeutic drugs used for the targeted therapy of various types of cancer. This work discusses the experimental and computational evaluation of chloranilic acid (CLA) as a universal chromogenic reagent for developing a novel 96-microwell spectrophotometric assay (MW-SPA) for TKIs. The reaction resulted in an instantaneous formation of intensely purple colored products with TKIs. Spectrophotometric results confirmed that the reactions proceeded via the formation of charge-transfer complexes (CTCs). The physical parameters were determined for the CTCs of all TKIs. Computational calculations and molecular modelling for the CTCs were conducted, and the site(s) of interaction on each TKI molecule were determined. Under the optimized conditions, Beer's law correlating the absorbances of the CTCs with the concentrations of TKIs were obeyed in the range of 10-500 µg/well with good correlation coefficients (0.9993-0.9998). The proposed MW-SPA fully validated and successfully applied for the determination of all TKIs in their bulk forms and pharmaceutical formulations (tablets). The proposed MW-SPA is the first assay that can analyze all the TKIs on a single assay system without modifications in the detection wavelength. The advantages of the proposed MW-SPA are simple, economic and, more importantly, have high throughput.

Synthesis and Studies of the Inhibitory Effect of Hydroxylated Phenylpropanoids and Biphenols Derivatives on Tyrosinase and Laccase Enzymes.

The impaired activity of tyrosinase and laccase can provoke serious concerns in the life cycles of mammals, insects and microorganisms. Investigation of inhibitors of these two enzymes may lead to the discovery of whitening agents, medicinal products, anti-browning substances and compounds for controlling harmful insects and bacteria. A small collection of novel reversible tyrosinase and laccase inhibitors with a phenylpropanoid and hydroxylated biphenyl core was prepared using naturally occurring compounds and their activity was measured by spectrophotometric and electrochemical assays. Biosensors based on tyrosinase and laccase enzymes were constructed and used to detect the type of protein-ligand interaction and half maximal inhibitory concentration (IC50). Most of the inhibitors showed an IC50 in a range of 20-423 nM for tyrosinase and 23-2619 nM for laccase. Due to the safety concerns of conventional tyrosinase and laccase inhibitors, the viability of the new compounds was assayed on PC12 cells, four of which showed a viability of roughly 80% at 40 µM. In silico studies on the crystal structure of laccase enzyme identified a hydroxylated biphenyl bearing a prenylated chain as the lead structure, which activated strong and effective interactions at the active site of the enzyme. These data were confirmed by in vivo experiments performed on the insect model Tenebrio molitur.

Qualitative and quantitative assay of glucose 6 phosphate dehydrogenase in patients attending tertiary care center.

OBJECTIVES: The study was carried out with the aim to find out the frequency of Glucose 6 phosphate dehydrogenase (G6PD) deficiency among the patients attending the hospital and to rationalize the qualitative methemoglobin reduction test in reference to the quantitative spectrophotometric assay. Timely screening of the patients for G6PD with appropriate screening method can play an important role in preventing hemolytic crisis that arises from therapeutic use of oxidative drugs like primaquine. RESULT: The frequency of G6PD deficient cases was 3% by both of the employed tests. The mean ± SD of G6PD activity in the patients under study was 15.34 ± 4.7 IU/g Hb in males and 16.01 ± 3.74 IU/g Hb in females. G6PD activity was positively associated with reticulocyte count (r = 0.289, p value = 0.004) and negatively with mean corpuscular hemoglobin concentration (r = -0.220, p-value = 0.028). The correlation of red blood corpuscular count and G6PD was statistically significant (p-value = 0.048).

Ferric-bipyridine assay: A novel spectrophotometric method for measurement of antioxidant capacity.

Measurement of the antioxidant potential using in vitro assays is paramount in the assessment of various food products and nutraceuticals. Researchers always attempt to develop more accurate assays which can be performed in unsophisticated conditions. This novel method, Ferric-Bipyridine reducing capacity of total antioxidants (FBRC) is a very simple, accurate assay performed based on the reduction of Fe (III) to Fe (II) by antioxidants with the formation of a colored complex with bipyridine (Bp) i.e, Fe(II)-Bp. The FBRC method thus developed was assessed under carefully adjusted parameters of oxidant concentration, pH, temperature, solvent, light and time in order to fix the optimum conditions for the assay. The spectrophotometric monitoring of Fe(II)-Bp complex was noted by the formation of an intense pink color at room temperature with absorption maxima at 535 nm, pH 4. The analytical performance of this method was fully validated, and the obtained results were satisfactory. It was successfully applied to measure the total antioxidant capacity of standard compounds such as gallic acid, ascorbic acid and butylated hydroxy toluene (BHT), in addition to some plant extracts and oils. The FBRC method is inexpensive, reproducible and simple to perform. In addition, the antioxidant activity of the tested compounds compared to common reference methods showed that the novel FBRC method is superior to the Ferric reducing antioxidant power (FRAP) with regard to its use of realistic pH and faster kinetics. Thus, the FBRC method is convenient for the estimation of total antioxidant in plants extracts, natural products, essential oils and food stuff.

Spectrophotometric Assays to Quantify the Activity of T4SS ATPases.

Biogenesis of T4SS apparatus and substrate transport require energy. Conjugative T4SS have three ATPases that enable DNA processing and transport of the nucleoprotein complex to the recipient cell. In the conjugative plasmid R388, these ATPases are named TrwB, TrwK, and TrwD. Here, three different spectrophotometric assays to measure the enzymatic properties of these ATPases are described. The choice of the assay will depend on the specific requirements of each enzyme.

Isolation of a tyrosinase inhibitor from unripe grapes juice: A spectrophotometric study.

Grapes are known to contain high quantity of polyphenolic compounds, including caffeic, coumaric and ferulic acids esterified with tartaric acid, to yield caftaric, coutaric and fertaric acids, respectively. These acids are more abundant in unripe grapes, which can be processed into verjuice, a product that shows intrinsic resistance against microbial growth and significant antioxidant activity. In the present work, the isolation of hydroxycinnamoyl tartaric acids from unripe grape juice by chromatographic techniques was described. Moreover, the capability of caftaric acid to inhibit tyrosinase activity was evaluated by spectrophotometric assays. According to the kinetics parameters calculated, caftaric acid was shown to be a competitive inhibitor of tyrosinase, more potent than the related caffeic and chlorogenic acids, suggesting that it can be used in cosmetic and food industries for the development of natural skin whitening formulations and as an agent able to counteract the enzymatic browning of food.