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Isocitrate lyase (EC. 4.1.3.1) has been partially purified from extracts of the unicellular green alga Gloeomonas sp. grown either photoautotrophically in CO2 or photoheterotrophically with acetate resulting in a 50-fold increase in specific activity. Enzyme preparations from both cultures were eluted from DEAE-cellulose columns at almost the same position. The enzymes showed classical Michaelis kinetics with Km values of 1.14 and 1.4 mM and responded in a similar manner to metabolites. Glycol-late, 3-phosphoglycerate, ribulose diphosphate, α-ketoglutarate, succinate, malate, fumarate, and ADP inhibited the enzyme at concentrations of 10 mM. Inhibition by oxaloacetate occurred at 1 mM. Succinyl-CoA (1 mM) activated the enzyme to 155% of the control. These results are discussed in relation to the autotrophic and photoheterotrophic mode of nutrition in algae.

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