THE EFFECTS OF N-THIOPHOSPHORYL AMINO-ACIDS ON THE ACTIVITY OF GREEN CRAB (SCYLLA-SERRATA) ALKALINE-PHOSPHATASE

Green crab (Scylla Serrata) alkaline phosphatase (EC 3.1.3.1) is a met alloenzyme which catalyzed the nonspecific hydrolysis of phosphate mon oesters. In the present paper, the effects of several N-thiophosphoryl amino acids on the activity of green crab alkaline phosphatase have b een studied. The results show that these derivatives of amino acids ca n lead to reversible inactivation. The equilibrium constants for inhib itors binding with the enzyme and/or the enzyme-substrate complexes ha ve been determined. The obtained results show that both N-thiophosphor yl-Cys and N-thiophosphoryl-Glu were non-competitive inhibitors, while other five N-thiophosphoryl amino acids were un-competitive inhibitor s. For the un-competitive inhibitors, the inhibition strength follows the order N-thiophosphoryl-Ile > -Val > -Lys > -Ala > -Tyr. Compared w ith respective free amino acids, it can be seen that N-thiophosphoryla tion of the amino acids inc-eased their inhibition strength except the N-thiophosphoryl-Cys.