Catabolism of L tyrosine by the homoprotocatechuate pathway in gram positive bacteria

Abstract

A metabolic pathway for L tyrosine catabolism involves 3,4 dihydroxyphenylacetic acid (homoprotocatechuic acid) as substrate for fission of the benzene nucleus. Cell extracts of an organism tentatively identified as a Micrcoccus possessed the enzymes required for degrading homoprotocatechuate to succinate and pyruvate, and stoichiometry was established for several of these reactions. When the required coenzymes were added, cell extracts degraded L tyrosine to the ring fission product of homoprotocatechuate 2,3 dioxygenase and also converted 4 hydroxyphenylpyruvic into 4 hydroxyphenylacetic acid. This compound, in turn, gave stoichiometric amounts of the ring fission product of homoprotocatechuate by the action of a nicotinamide adenine dinucleotide phosphate dependent 3 hydroxylase coupled with homoprotocatechuate 2,3 dioxygenase. Evidence is presented that this route for L tyrosine catabolism is yaken by five other gram positive strains, including Micrococcus lysodeikticus and a species of Bacillus. Five other gram positive bacteria from other genera employed the alternative homogentisate pathway.