ROLE OF SULFHYDRYL GROUPS IN THIAMINE KINASE ENZYMATIC ACTIVITY MANIFESTATION IN PIG BRAIN

With the help of mercaptide-forming reagents, HgCl2 and p-chloromercury benzoate the amount and reactivity of SH-groups of pig brain thiamine kinase was determined. The enzyme molecule was demonstrated to contain two types of sulfhydryl groups: the first one is easily accessible and fast interacting; the second one - partially hidden and “sluggish” reactive. Modification of the first type SH group by p-chloromercury benzoate lead to 36 % reduction of enzymatic reaction rates, while modification of the second type SH group resulted in complete thiamine kinase inactivation. Mercaptide-forming reagents have different blocking activity because of their different chemical nature. While p-chloromercury benzoate taken in equivalent proportions with protein forms one chemical bond: protein?S?HgR, HgCl2 probably forms two. The substrate is thiamine, but not ATP and magnesium ions only partially protect thiamine kinase from p-chloromercury benzoate induced inactivating action. It is possible to assume that SH-groups do not directly participate in the process of vitamin B1 biotransformation, but are localized in sorption areas of the protein active center thus stabilizing its structure.