PubMed Health⌕ Search

Biomedical subjects

M Zajac

Publications and source records attributed to M Zajac.

At least 37 records · Page 2Linked to original sources
PubMed1986

Crystallization and preliminary diffraction studies of the Lys-49 phospholipase A2 from Agkistrodon piscivorus piscivorus.

Previous chemical and structural studies have proposed a major role for Asp-49 in the calcium-mediated activation of phospholipases A2. Recently, a new class of phospholipases A2 has been characterized with a lysine in the place of aspartate at position 49 (Maraganore, J. M., Merutka, G., Cho, W., Welches, W., Kézdy, F. J., and Heinrikson, R. L. (1984) J. Biol. Chem. 259, 13839-13843; Maraganore, J. M., and Heinrikson, R. L. (1986) J. Biol. Chem. 261, 4797-4804). Although both the Lys-49 and Asp-49 phospholipases require calcium for enzymatic activity, the Lys-49 enzymes appear to be unique in their ability to bind phospholipids prior to undergoing calcium-mediated activation. We have successfully crystallized the Lys-49 phospholipase A2 from the venom of the American cottonmouth water moccasin (Agkistrodon piscivorus piscivorus). The crystals are tetragonal, the space group being P4(1)2(1)2 or P4(3)2(1)2 with unit cell dimensions of a = b = 71.05 A, and c = 57.76 A. There is only one molecule in the asymmetric unit and the crystals provide good quality diffraction data to 2.2 A.

Crystallization↗
PubMed1981

Kinetics of drug decomposition. Part 66. Kinetics of the hydrolysis of carphecillin in aqueous solution.

The rates of hydrolysis of the beta-lactam ring in the pH range 1.77--9.22 at 294, 303, 313 and 233 K and of the ester bond in the pH range 0.43--8.78 at 273, 283, 294, 303, 313 and 323 K for carphecillin have been investigated. The rate constants were determined for the reactions catalyzed by H+ and OH- ions and moreover for the hydrolysis of the beta-lactam ring catalyzed by undissociated acids and anionic bases. The thermodynamic parameters were calculated for particular reactions. In the acidic medium carphecillin is significantly more stable than carbenicillin. In the alkaline medium the rate of inactivation of carphecillin and carbenicillin is the same because carbenicillin is formed from carphecillin as the result of the very fast hydrolysis of the ester bond.

Carbenicillin↗
PubMed1976

Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part 1. Log k--pH profile for sulfadimidine solvolysis.

The degradation of sulfadimidine (SDMP) in the pH range 5-83--10-0, at 403, 411 and 418 K, was investigated by UV spectrophotometry. Semilogarythmic plots (A242--A') vs. time in 0-1 M HCl for the degradation of SDMP in the above pH range were linear. The log k--pH profile constructed from the experimental results served for estimation of specific rate constants and pKa values. These, in turn, were used to calculate the theoretical log k--pH profile, acc. to the equation for the rate of reaction proportional to the concentration of the dissociated form of SDMP, in the pH range 5-8--10. Thermodynamic parameters of the reaction--energy, entropy and enthalpy of activation and the frequency factor for the specific rate constants were determined.

Chromatography, Paper↗
PubMed1976

Kinetics and mechanism of degradation of some 2-sulfanilamidopyrimidine derivatives. Part 2. Log k--pH profile for sulfadimidine autoxidation.

The overall first order rate constants for the reaction of degradation of sulfadimidine (kobs. = kOX+kh) in the presence of the air oxygen were determined from the measurements of absorbance in 0-1 M HCl at 243 nm, using "the feathering technique". The apparent first order rate constants for autoxidation of sulfadimidine at 403, 411 and 418 K, in the pH range 2-0--9-2 were calculated from the equation kOX = kobs. -- kh, where kh are the rate constants for hydrolysis carried out under nitrogen. The rate of sulfadimidine autoxidation is a function of concentration of the undissociated form (kOX = kOX-fHA). The thermodynamic parameters of the reaction: Ha, deltaHNo., deltaSNo. and logA were determined for the specific rate constant of autoxdiation (kOX).

Drug Stability↗