Chemical modification of Saccharomycopsis fibuligera R64 α-amylase to improve its stability against thermal, chelator, and proteolytic inactivation.

α-Amylase catalyzes hydrolysis of starch to oligosaccharides, which are further degraded to simple sugars. The enzyme has been widely used in food and textile industries and recently, in generation of renewable energy. An α-amylase from yeast Saccharomycopsis fibuligera R64 (Sfamy) is active at 50 °C and capable of degrading raw starch, making it attractive for the aforementioned applications. To improve its characteristics as well as to provide information for structural study ab initio, the enzyme was chemically modified by acid anhydrides (nonpolar groups), glyoxylic acid (GA) (polar group), dimethyl adipimidate (DMA) (cross-linking), and polyethylene glycol (PEG) (hydrophilization). Introduction of nonpolar groups increased enzyme stability up to 18 times, while modification by a cross-linking agent resulted in protection of the calcium ion, which is essential for enzyme activity and integrity. The hydrophilization with PEG resulted in protection against tryptic digestion. The chemical modification of Sfamy by various modifiers has thereby resulted in improvement of its characteristics and provided systematic information beneficial for structural study of the enzyme. An in silico structural study of the enzyme improved the interpretation of the results.

Bioequivalence study of two azithromycin formulations in healthy subjects.

The study was conducted to find out whether the bioavailability of a 500 mg azithromycin (CAS 83905-01-5) tablet (Zycin, test) was equivalent to that of a reference formulation. The pharmacokinetic parameters assessed in this study were the area under the plasma concentration-time curve from time zero to 120 h (AUCt), area under the plasma concentration-time curve from time zero to infinity (AUCinf), the peak plasma concentration of the drug (Cmax), time needed to achieve the peak plasma concentration (tmax), and the elimination half-life (t1/2). This was a randomized, single blind, two-period, cross-over study which included 18 healthy adult male and female subjects under fasting conditions. In each of the two study periods (separated by a washout of two weeks) a single dose of test or reference drug was administered. Blood samples were taken up to 120 h post dose, the plasma was separated and the concentrations of azithromycin were determined by a LC-MS/MS method. In this study, the mean AUCt, AUCinf, Cmax, and t1/2 of azithromycin from the test drug were 4967.49 ng x h x mL(-1), 5871.74 ng x h x mL(-1), 412.14 ng/mL, and 51.32 h, respectively. The mean AUCt, AUCinf, Cmax, and t1/2 of azithromycin from the reference drug were 4276.75 ng x h x mL(-1), 5578.12 ng x h x mL(-1), 419.89 ng/mL, and 51.23 h, respectively. The median tmax of he test drug and reference drug were 3.0 h and 2.0 h, respectively. The geometric mean ratios (90% CI) of the test drug/reference drug for azithromycin were 101.56% (86.61-119.08%) for AUCt, 101.27% (84.97-120.70%) for AUCinf, and 97.78% (84.50-113.16%) for Cmax. Based on this study, it was concluded that the two azithromycin tablets (test and reference drug) were bioequivalent in terms of the rate and extent of absorption.