SEQUENCE OF THE HPCG AND HPCC GENES OF THE META-FISSION HOMOPROTOCATECHUIC ACID PATHWAY OF ESCHERICHIA-COLI-C - NEARLY 40-PERCENT AMINO-ACID IDENTITY WITH THE ANALOGOUS ENZYMES OF THE CATECHOL PATHWAY

The meta-fission pathway for homoprotocatechuic acid (HPC) catabolism is chemically analogous to the oxidative meta-fission pathway for cate chol degradation and so provides an opportunity to investigate how the enzymes of chemically similar, but specific, pathways might have aris en. Two more genes of the HPC pathway from Escherichia coli C, hpcC, e ncoding 5-carboxymethyl-2-hydroxymuconic acid semialdehyde (CHMS) dehy drogenase, and hpcG, encoding 2-oxohept-3-ene-1,7-dioic acid (OHED) hy dratase, have now been sequenced to aid this analysis. The CHMS dehydr ogenase showed 40% amino acid (aa) sequence identity with the correspo nding enzyme of the catechol pathway, and the OHED hydratase showed 36 % aa sequence identity with the catechol pathway hydratase. The CHMS d ehydrogenase is a member of the aldehyde dehydrogenase superfamily tha t includes enzymes from animal, plant and microbial sources. Since it appears that the dioxygenase, isomerase and decarboxylase enzymes of t he two pathways are not closely related, it is proposed that the two s ets of enzymes have arisen separately, but with the muconic acid semia ldehyde dehydrogenases and the hydratases being recruited, respectivel y, from the same ancestral sources.