Isocitrate Dehydrogenases and NADP‐Alcohol Dehydrogenase of Euglena gracilis var. bacillaris*

Abstract

SYNOPSIS. Nicotinamide adenine dinucleotide phosphate (NADP) and nicotinamide adenine dinucleotide (NAD) linked isocitrate dehydrogenase and NADP linked alcohol dehydrogenase have been detected in Euglena gracilis var. bacillaris.The NADP isocitrate dehydrogenase showed half‐maximal activity at a concentration of 3 × 10−5 M DL‐isocitrate, but did not follow simple Michaelis‐Menten kinetics with respect to substrate concentration. The optimal NADP concentration was about 0.06 mM, and activity fell off sharply on either side of this optimum. Fresh preparations of the enzyme migrated as single bands in disc electrophoresis, but two enzymatically active bands were present after frozen storage.The NAD isocitrate dehydrogenase followed Michaelis‐Menten kinetics with respect to substrate. In crude extracts, no requirement for adenosine monophosphate, adenosine diphosphate, or sulfhydryl compounds could be found.NADP alcohol dehydrogenase activity could be found with either ethanol or propanol as substrate. Low concentrations of coenzyme A were moderately inhibitory.In tris(hydroxymethyl) aminomethane buffer (tris buffer), Euglena extracts reduced NAD slowly in the absence of exogenous substrate. In the absence of tris, no such reduction occurred. A similar phenomenon was observed with NADP.