Mechanism of L-Alloisocitric Acid Fermentation: Isocitrate Epimerase Activity in the Cell-free Extract of Penicillium purpurogenum

Abstract

Isocitrate epimerase activity catalyzing the reversible epimerization between threo-D-isocitrate and erythro-L-isocitrate (L-alloisocitrate) was determined in the cell-free extract of Penicillium purpurogenum rubrisclerotium, which accumulated a large amount of the latter acid from glucose.

The presence of 15 mM or a higher concentration of citrate was essential for detection of the activity in vitro. The epimerase was located in mitochondoria and seemed to require structural organization in cells for its full activity. A pathway was proposed in fungal cells for accumulation of erythro-L-isocitrate through threo-D-isocitrate. An enzymological method to determined radioactive erythro-L-isocitrate was developed using a specific bacterial dehydrogenase.