چكيده لاتين :
Three iso-alkyldithiocarbonates (xanthates), as sodium salts, C3H70CS2Na (I), C4H90CS2Na (II) and C5H110CS2Na (III) were synthesized, by the reaction between CS2 and the corresponding iso-alcohol in the presence of NaOH. These compounds were examined for inhibition of cresolase activity of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. 4-[(4-methylphenyl) azo]-phenol (MePAPh) were used as synthetic substrate for the enzyme for the cresolase reaction. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for the three xanthates. For cresolase activity, I and II showed a mixed inhibition pattern but III showed a competitive inhibition pattern. These new synthesized compounds are potent inhibitors of MT with K, values of 9.8, 7.2 and 6.1 microM for cresolase inhibitory activity, for compound-I, - compound-II and compound-Ill, respectively. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (a > 1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds in cresolase activity. The cresolase inhibition is related to the chelating of the copper ions at the active site by a negative head group (S ) of the anion xanthate, which leads to similar values of K, for all three xanthates.
