Regulation ofTryptophan Pyrrolase Activity inXanthomonas pruni

Tryptophan pyrrolase was studied inpartially purified extracts ofXanthomonas pruni. Thedialyzed enzymerequired bothhemeandascorbate formaximal activity. Otherreducing agents wereable tosubstitute forascorbate. Protoporphyrin competed withhemefortheenzyme,suggesting that thenative enzymeisahemoprotein. Theenzyme exhibited sigmoid saturation kinetics. Reduced nicotinamide adenine dinucleotide (NADH),reduced nicotinamide adenine dinucleotide phosphate (NADPH),nicotinic acidmononucleotide, andanthranilic acidenhanced the sigmoid kinetics andpresumably boundtoallosteric sites on theenzyme.The sigmoid kinetics werediminished inthepresenceofa-methyltryptophan. NAD, NADP,nicotinic acid, nicotinamide, nicotinamide mononucleotide, andseveral other related compounds werewithout effect on theactivity oftheenzyme.These dataindicate thattheactivity oftheenzymeisunderfeedback regulation bythe ultimate endproducts ofthepathway leading toNAD biosynthesis, aswell asby certain intermediates ofthis pathway.