Purification andProperties ofFormylglutamate Amidohydrolase fromPseudomonas putidat

was notasubstrate fortheenzyme,butbothit andN-formyl-L-aspartate werecompetitive inhibitors offormylglutamate hydrolysis, exhibiting Kivalues of6 and9mM,respectively. Theabsence ofFGaseactivity asan integral partofhistidine breakdown inmostother organisms andthesomewhat uncoordinated regulation ofFGasesynthesis withthatoftheother hutenzymes inPseudomonas suggest thatthegeneencoding itssynthesis may haveevolved separately fromtheremaining hutgenes. Histidine isutilized asbotha carbon andnitrogen source by a widerange ofmicrobial species, andthisprocess involves theformation ofglutamate plusammoniaandaC-1 unitatthelevelofformate as keyintermediates. The pathway leading fromhistidine toglutamate ismadeup of either fouror fivereactions, depending on theorganism studied. Thefirst three steps arecommon toallandresult in theformation ofN-formimino-L-glutamate (FIGLU). The precise routeforthesubsequent breakdown ofFIGLU differs among organisms. InSalmonella typhimurium (21), Klebsiella aerogenes (19), andBacillus subtilis (6,13), FIGLU ishydrolyzed toL-glutamate andformamide by N-formimino-L-glutamate formiminohydrolase