Nicotinamide-adenine dinucleotide glycohydrolase of Mycobacterium tuberculosis H37Rv

Abstract

The optimum conditions for the heat-activation of the enzyme nicotinamide-adenine dinucleotide (NAD) glycohydrolase present in an inhibited state in the crude cell-free extracts of the virulent strain of Mycobacterium tuberculosis H37Rv was described. The heat-activated enzyme was partially purified by fractionation, isoelectric precipitation and Ca3(PO4)2-gel adsorption. The optimum conditions of temperature, pH, substrate and enzyme concentrations are presented, and the Km values for both the substrates (NAS and NADP) are given. The enzyme differs from the NAD glycohydrolases of other microorganisms in having a sharp pH optimum and equal reactivity towards NAD and NADP. The effect of various inhibitors and antitubercular agents on the partially purified enzyme was studied. The inhibitor with which the enzyme is associated in the crude cell-free extracts is specific for the enzyme from this source. However, the inhibitor from the avirulent strain M. tuber-culosis H37Ra was inhibitory for the partially purified enzyme from the virulent strain to an equal extent. An excess of free inhibitor is present in the crude cell-free extracts, and the complex formed between the enzyme and its inhibitor is undissociable.