Effect of Inhibitors on Ammonia-, 2-Oxoglutarate-, and Oxaloacetate-Dependent O2 Evolution in Illuminated Chloroplasts

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Abstract
The evolution of O2 in spinach chloroplasts in the presence of oxaloacetate (OAA) was inhibited by a wide range of dicarboxylates. In contrast, (ammonia, 2-oxoglutarate)-dependent O2 evolution was stimulated by malate, succinate, fumarate, glutarate, maleiate, and l-tartrate although OAA has little effect. This increase in O2 evolution was accompanied by a similar increase in 14C incorporation from [5-14C]oxoglutarate into amino acids which was sensitive to azaserine inhibition. Glutamate and aspartate inhibited (ammonia, 2-oxoglutarate)-dependent O2 evolution, but this inhibition was relieved by the addition of succinate, malate, or fumarate. OAA-dependent O2 evolution also was inhibited by glutamate and aspartate, but succinate, malate, or fumarate had little effect on this inhibition. Phthalonate and n-butyl malonate inhibited (ammonia, 2-oxoglutarate)-dependent O2 evolution competitively with respect to 2-oxoglutarate and uncompetitively with respect to malate. Both these inhibitors inhibited OAA-dependent O2 evolution competitively. This evidence suggests that different mechanisms might be involved in the transport of OAA, 2-oxoglutarate, and malate into the chloroplasts.