VICINAL THIOLS ARE INVOLVED IN INOSITOL 1,2,3,5,6-PENTAKISPHOSPHATE 5-PHOSPHATASE ACTIVITY FROM FETAL CALF THYMUS

Inositol 1,2,3,5,6-pentakisphosphate (Ins(1,2,3,5,6)P-5) 5-phosphatase present in fetal calf thymus has been partially purified. This enzyme was inhibited dose-dependently by different thiol modifiers like N-et hylmaleimide (NEM), p-chloromercuribenzene sulfonate (PCMBS), diamide, and phenylarsine oxide (PAO). The inhibition by PCMBS and diamide was protected by preincubation with dithiothreitol (DTT) and the phosphat ase substrate, Ins(1,2,3,5,6)P-5. Diamide, a compound that specificall y modifies vicinal thiol groups, also blocked the 5-phosphatase dose-d ependently. Specificity of this blockade was proven by using dimercapt opropanol (DMP), a compound known to protect vicinal thiol groups. DMP prevented the enzyme from inhibition by diamide. These data suggest t hat vicinal thiols are involved in Ins(1,2,3,5,6)P-5 5-phosphatase act ivity. (C) 1997 Academic Press.