Purification and Characterisation of Sarcosine Dehydrogenase

Abstract

Sarcosine dehydrogenase was purified to homogeneity from Pseudomonas fluorescens induced in TSB medium by sarcosine. The enzyme in a cell-free extract was initially bound to the hydrophobic matrix phenyl-Sepharose in low ionic strength buffer and eluted with Triton X-100. FPLC anion-exchange and gel-filtration was performed using Mono-Q and Superose-12 matrices respectively. Final chromatofocusing with Mono-P gave homogeneous enzyme, as shown by a single protein band silver-stained on a PAGE gel.

The purified enzyme catalysed the dehydrogenation of the N-methyl amino-acids, methylhydantoin, N,N-dimethylglycine, N-methyl-DL-alanine, N-methyl-DL-valanine and Nmethyl-L-leucine. The Km and Vmax values for sarcosine were l.9mmolL⁻¹ and 6.60µxmol min⁻¹ respectively. Maximum initial activity was obtained at pH 9.0 and 40°C. The isoelectric point was determined as pH 4.8. Native molecular weight was estimated at about 180,000 consisting of two sub-units of 95,000. Enzyme activity was inhibited by a variety of sulphydryl reagents including p-hydroxymercuribenzoate and phenylmercuric nitrate. Activity was not stimulated by the presence of metal ions nor was their presence required for activity.