Reversible inactivation of thiaminase I of Bacillus thiaminolyticus by its primary substrate, thiamine.

Thiaminase I of Bacillus thiaminolyticus is reversibly inactivated when it is incubated with its primary substrate, thiamine, or with one of several structural analogues of thiamine in the absence of an acceptor base. The inactivation reaction is pH and temperature dependent and is stochiometric with respect to thiamine and thiaminase I concentrations. One molecule of thiamine is cleaved for each molecule of enzyme inactivated. Inactivation is prevented or reversed by sulfhydryl-reducing agents. Active or reactivated thiaminase I migrate as a single band in polyacrylamide electrophoresis gels. Inactive thiaminase I appears to migrate as two separate bands. Active, inactive, and reactivated thiaminase I are immunologically similar. A possible mechanism for the inactivation of thiaminase I by its substrate is discussed.