1. Behaviour of L-gamma-glutamyl-4-nitroanilide and L-gamma-glutamyl-3-carboxy-4-nitroanilide with respect to gamma-glutamyltransferases of different origin
P M Verhoeff, F P Peters, H Steigstra, J C Hafkenscheid Clin Chim Acta. 1988 Jul 15;175(2):129-34. doi: 10.1016/0009-8981(88)90002-2.
In this paper we compare the measurement of catalytic activity concentrations of gamma-glutamyltransferase with the non-carboxylated and the carboxylated substrate in preparations of different origin. Fresh human sera, commercial test sera and preparations of gamma-glutamyltransferase purified from human liver, porcine kidney and bovine kidney were used as sample materials. When assayed with both substrates preparations of gamma-glutamyltransferase from bovine kidney behaved in a different manner as did the enzyme in preparations from human liver or porcine kidney and the enzyme in fresh human sera. On account of the results obtained with both substrates we classified the commercial test sera for their enrichment using multi-inductive component analysis. The differences observed for the various methods of determination seem to have significance in quality control.
2. Kinetic peculiarities of human tissue kallikrein: 1--substrate activation in the catalyzed hydrolysis of H-D-valyl-L-leucyl-L-arginine 4-nitroanilide and H-D-valyl-L-leucyl-L-lysine 4-nitroanilide; 2--substrate inhibition in the catalyzed hydrolysis of N alpha-p-tosyl-L-arginine methyl ester
Marinez O Sousa, Tânia L S Miranda, Caroline N Maia, Eustáquio R Bittar, Marcelo M Santoro, Amintas F S Figueiredo Arch Biochem Biophys. 2002 Apr 1;400(1):7-14. doi: 10.1006/abbi.2002.2764.
Hydrolysis of D-valyl-L-leucyl-L-lysine 4-nitroanilide (1), D-valyl-L-leucyl-L-arginine 4-nitroanilide (2), and N alpha-p-tosyl-L-arginine methyl ester (3) by human tissue kallikrein was studied throughout a wide range of substrate concentrations. At low substrate concentrations, the hydrolysis followed Michaelis-Menten kinetics but, at higher substrate concentrations, a deviation from Michaelis-Menten behavior was observed. With the nitroanilides, a significant increase in hydrolysis rates was observed, while with the ester, a significant decrease in hydrolysis rates was observed. The results for substrates (1) and (3) can be accounted for by a model based on the hypothesis that a second substrate molecule binds to the ES complex to produce a more active or an inactive SES complex. The deviation observed for substrate (2) can be explained as a bimolecular reaction between the enzyme-substrate complex and a free substrate molecule.
