1. 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.
2. L-Pyroglutamyl-L-phenylalanyl-L-leucine-p-nitroanilide--a chromogenic substrate for thiol proteinase assay
Filippova IYu, E N Lysogorskaya, E S Oksenoit, G N Rudenskaya, V M Stepanov Anal Biochem. 1984 Dec;143(2):293-7. doi: 10.1016/0003-2697(84)90665-1.
L-Pyroglutamyl-L-phenylalanyl-L-leucine-p-nitroanilide (PFLNA)--a convenient chromogenic substrate for assay of thiol proteinases papain, ficin, and bromelain--was prepared by enzymatic synthesis with chymotrypsin as a catalyst. The thiol proteinases hydrolyze PFLNA with the liberation of p-nitroaniline, estimated spectrophotometrically by its absorbance at 410 nm. The phenylalanine residue in the P2 position of PFLNA meets the specificity demands of thiol proteinases. The following values of Km were found for PFLNA hydrolysis: by papain, 0.34 mM; by ficin, 0.43 mM; by bromelain, 0.30 mM. This substrate was successfully applied to monitor thiol proteinase affinity chromatography on bacitracin-Sepharose, which resulted in a 2- to 4-fold purification from commercial preparations.
3. The role of ASCT2 in cancer: A review
Yang Liu, Tingli Zhao, Zhengzheng Li, Lai Wang, Shengtao Yuan, Li Sun Eur J Pharmacol. 2018 Oct 15;837:81-87. doi: 10.1016/j.ejphar.2018.07.007. Epub 2018 Jul 17.
Reorganization of cellular metabolism is one of the hallmarks of cancer and many tumors show high glucose uptake and glutamine addiction. Glutamine is imported by the SLC family transporters from the microenvironment, and ASCT2 (encoded by the SLC1A5 gene) is recognized as a primary transporter. Of note, ASCT2 is overexpressed in different cancers and is closely related to poor prognosis. Nonetheless, the mechanisms regulating ASCT2 activity has not been elucidated. Moreover, several inhibitors of ASCT2 have emerged and shown a surprising antitumor effect. In conclusion, this review describes the function, regulatory mechanism, and inhibitors of ASCT2 in cancer, suggesting that high expression of ASCT2 is a promising prognostic marker and a potential drug target.
