Repression of thiaminase I by thiamine and related compounds in Bacillus thiaminolyticus

The extracellular enzyme thiaminase I from Bacillus thiaminolyticus is repressible by thiamine. Either one of the heterocyclic moieties of this vitamin supported limited growth of this organism but had no effect on thiaminase I production. However, a combination of these two resulted in optimal growth and partial repression of this enzyme. The products of the base exchange reaction catalyzed by thiaminase I are not functional in repression when present alone. The simultaneous presence of both reaction products, i.e., N-[5-(4-amino-2-methylpyrimidinyl)] methyl aniline and 5-(2′-hydroxy-ethyl)-4-methylthiazole, can replace the vitamin B1 requirement for growth and give the same degree of enzyme repression. Neither pyrithiamine nor oxythiamine inhibited growth of the organism when present in a 100:1 molar ratio to thiamine. Pyrithiamine and vitamin B1 repressed thiaminase I to approximately the same extent, whereas oxythiamine was only partially functional in this process.