Exchange reactions catalyzed by methioninase from Pseudomonas putida. Isolation and characterization of the exchange products

Gel-electrophoretically homogeneous methioninase [L-methionine methanethiol-lyase (deaminating), EC 4.4.1.11] of Pseudomonas putida, which catalyzes alpha, beta- and alpha, gamma-eliminations from S-substituted amino acids, could also catalyze a variety of beta- and gamma-exchange reactions, according to the following equations: RSCH2CH(NH2)COOH+R'SH in equilibrium R'SCH2CH(NH2)COOH+RSH (beta-exchange) and RSCH2CH2CH(NH2)COOH+R'SH in equilibrium R'SCH2CH2CH(NH2)COOH+RSH (gamma-exchange), where R'SH represents an exogeneously added alkanethiol or a substituted thiol. Related amino acids not available for elimination reactions appeared to be inert as substrates for exchange. The maximum activity for the exchange reactions was observed at pH 8.5 in potassium pyrophosphate buffer. The activity increased linearly with the increase in protein concentration from zero to 3.0 mug per ml, and with incubation time up to at least 15 min at 30 degrees. Some of the exchange reaction products were purified by a combination of paper and ion exchange chromatographies, and charcoal treatment: their structures were confirmed by physicochemical methods including elemental analysis and proton magnetic resonance, infrared, and mass spectrometries.