An analysis of molecular polymorphism of esterase M produced by motile Aeromonas strains

The high levels of electrophoretic polymorphism of esterase M detected in eight distinct hybridization groups of motile Aeromonas raise questions of genetic homogeneity of the electromorphs. The 40 electromorphs detected fall in four Mr classes--75, 80, 90, and 110 kD--and one typical variant belonging to each of these classes was purified. The four purified esterases exhibited the same resistance to heat, to pH and to diisopropyl fluorophosphate, the same Km values for 1-naphthyl acetate and 1-naphthyl propionate (1 mM), and immunological cross-reactions. Within each class, the electromorphs appeared to be related in term of single amino acid substitutions as estimated from their comparative titration patterns. The titration curves of the four purified esterases were strictly parallel suggesting close structural similarities. Thus, despite considerable variation in their pI, MF, and Mr values, it seems likely that the variants of esterase M are the products of closely related loci originating from a common ancestral gene.