Evidence for the existence of isocitrate lyase activity in methylotrophicHyphomicrobiumstrains

Abstract

Isocitrate lyase activities were detected in a range of 0.096–0.212 units mg−1 in cell-free extracts of all tested Hyphomicrobium strains grown on methanol as a sole carbon source, although the activities were rapidly lost during storage at 4 °C. When cell-free extracts were incubated with dithiothreitol, after storage the recovery of activity was observed, indicating the involvement of a labile sulfhydryl group in the enzyme. This confirmed the distribution of unstable isocitrate lyase in the genus Hyphomicrobium, and, contrary to previous observations, the operation of the ic+-serine pathway was suggested for the assimilation of one-carbon compounds.