ABSTRACT
The fluorescence and synchronous fluorescence spectra were employed to study the binding between sodium azide (NaN3) and horseradish peroxidase (HRP), which was affected by the molecular conformation and the microenvironment of the fluorescence residues. The mechanism of the fluorescence quenching of HRP by NaN3 was discussed and the binding constant and the number of binding sites of non-covalent bond between them were calculated.
Subject(s)
Fluorescence , Horseradish Peroxidase/chemistry , Sodium Azide/chemistry , Spectrometry, Fluorescence/methods , Algorithms , Binding Sites , Horseradish Peroxidase/metabolism , Kinetics , Protein Binding , Research Design , Sodium Azide/metabolismABSTRACT
Comparing the fluorescence spectra of tobacco peroxidase I (TOP I) solution and the solutions titrated by iodine anions, the number of binding locus and the binding constant of iodine anion to TOP I were calculated by using the modified Stern-Volmer equation. The mechanism of the quenching of fluorescence spectra and the distribution of tryptophane residues in the TOP I molecule were discussed.
Subject(s)
Nicotiana/enzymology , Peroxidase/chemistry , Plant Proteins/chemistry , Spectrometry, Fluorescence/methods , Algorithms , Anions/chemistry , Hydrogen-Ion Concentration , Iodine/chemistry , Kinetics , Peroxidase/metabolism , Plant Proteins/metabolism , Protein Binding , Research Design , TemperatureABSTRACT
The interaction of cystine and polyphenol oxidase (PPO) from nicotian tobaccum has been studied. The results show that cystine has an inhibitory effect on the enzymatic activity, the mechanism of which might be that the thiolether in cystine coordinates with Cu2+ in the active site of PPO, and the inactivation constant value of PPO by cystine is 0.633 min(-1), while the substrates or the products inhibit their combination. Cystine can also be combined with the products of enzymatic reaction to form a colourless compound. Cystine can inhibit the enzymatic activity completely when the molar ratio of cystine to PPO approaches 16,000:1. The effect of cystine on the fluorescence changes with the molar ratio of cystine to the PPO. However, when the molar ratio gets to 75:1, cystine has no longer the effect on either the fluorescence spectra or the synchronous spectra. Microenvironment of trp residue in PPO is more hydrophobic than that of free trp in water.
