An anti-cancer peptide was purified from the Mercenaria (Meretrix meretrix Linnaeus) by the method of chromatography on Sephadex G-25 and FPLC, and its molecular weight was determined to be 3147 Da by the way of MALDITOF mass spectrum. The effects of this peptide on human gastric gland carcinoma cells (BGC-823) and their cytoskeletal morphology were investigated. The results showed that the peptide could inhibit the proliferation of BGC-823 cells and obviously destroy the skeletal structures of the cells. When the concentration of the peptide reached 4.0μg/ml, the inhibition percentage of the cell growth was about 60%. The effects of this anticancer peptide on the activities of superoxide dismutase (SOD), alkaline phosphatase (ALP) and tyrosinase were studied. The results showed that the peptide activated ALP and SOD, but inhibit the tyrosinase activity. When the concentration of the peptide reached to 0.5μg/ml, the relative activities of SOD, ALP and tyrosinase were determined to be 188.5%, 122.0% and 27.5%, respectively.

Changes of activity and conformation of Ampullarium crossean-glucosidase in different concentrations of guanidine hydrochloride (GuHCl) have been studied by measuring the fluorescence spectra and its relative activity after denaturation. The fluorescence intensity of the enzyme decreased distinctly with increasing guanidine concentrations, the emission peaks appeared red shifted (from 338.4 to 350.8nm), whereas a new fluorescence emission peak appeared near 310nm. Changes in the conformation and catalytic activity of the enzyme were compared. A corresponding rapid decrease in catalytic activity of the enzyme was also observed. The extent of inactivation was greater than that of conformational changes, indicating that the active site of the enzyme is more flexible than the whole enzyme molecule. k+0>kβ+0 also showed that the enzyme was protected by substrate to a certain extent during guanidine denaturation.

Green crab (Scylla serrata) alkaline phosphatase (EC 3.1.3.1) is a metalloenzyme, which catalyzes the nonspeci

3,5-Dihydroxyphenyl decanoate (DPD) is found to inhibit the diphenolase activity of tyrosinase from mushroom (Agaricus bisporus). The effects of DPD on the diphenolase activity of mushroom tyrosinase have been studied. The results show that the enzyme activity decreases very slowly with an increase in DPD concentrations at lower concentrations of DPD (between 5 and 60μM). But at higher concentrations of DPD, DPD can strongly inhibit the diphenolase activity of the enzyme and the inhibition is irreversible. The IC50 value was estimated to be 96.5 lM. The inhibition mechanism of DPD has been investigated and the results show that DPD can bind to the free enzyme molecule and enzyme-substrate complex and lose the enzyme activity completely. The inhibition kinetics has been studied in detail by using the kinetic method of the substrate reaction described by Tsou. The microscopic rate constants of the enzyme inhibited by DPD at higher concentrations have been determined.

The inhibitory kinetics of the diphenolase of mushroom tyrosinase by seven p-alkoxybenzoic acids has been studied. The results show that these derivatives of benzoic acid behave as reversible inhibitors. Among them, p-hydroxybenzoic acid is competitive, while p-methoxybenzoic acid is non-competitive, p-ethoxybenzoic acid is mixed-II type, and the rest all behave as classical uncompetitive inhibitors. The inhibition constants of all of the seven compounds assayed, characterizing the inhibition, were evaluated. The models of the interactions between the enzyme and the inhibitors are compared.