REPLACEMENT OF THE COENZYME OF THIAMINASE BY CERTAIN NITROGEN COMPOUNDS

Many low-molecular nitrogenous substances of biological origin are activators of thiaminase both cyclic and aliphatic substances. Besides a polar grouping of basic character nitrogen in one form or another, all the activators contain in addition one other polar grouping, of acid character as a rule. Of the monocarboxylic amino acids studied, only glycine was found to be inactive. A particularly strong activating effect was shown by amino acids containing cyclic structures and sulfur also by the dipeptide carnosine. The dicarboxylic amino acids were not activators. For the activating effect to exist, it is not necessary that the active groupings of the nitrogen compound should be exclusively in the beta-and meta-positions relative to one another the alpha-amino acids also activate. The alkaloids nicotine and anabasine also activate thiaminase, although somewhat differently from the other activators. The substitute activators, according to our experiments with amino acids, compete with the coenzyme for the proteins, the affinity of the coenzyme for the protein being greater than the affinity of the substitute activators. The formation of the active apoenzyme coenzyme or apoenzyme substitute activator complex takes place by way of a reaction between sulfhydryl groups of the protein and the activating agent. The activity of the apoenzyme substitute activator complex is sometimes found to be higher than the activity of the apoenzyme coenzyme complex.