SUMMARY: Soluble extracts of bacteroids from soybean root nodules showed substantial rates of NAD and NADP reduction which were malate and MnCl dependent. Pyruvate was formed stoichiometrically and the NAD- and NADP-dependent rates were additive, indicating the presence of two malic enzymes. The NADP-dependent malic enzyme had a high affinity for malate (apparent = 0·1 mM) and was stimulated by ammonium. The NAD-dependent malic enzyme had a lower affinity for malate (apparent = 1·9 mM) and was stimulated by potassium and ammonium salts. The maximum velocities of the two enzymes were similar and of comparable magnitude to the activities of tricarboxylic acid cycle enzymes in the extracts. Possible roles of the malic enzymes in the metabolism of malate and succinate in bacteroids are discussed.


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