| Abstract: | Frankia vesicle clusters were prepared from root nodules ofAlnus incana (L.) Moench inoculated either with a local sourceof Frankia or with Frankia Cpll. The capacity of vesicle clustersto respire was investigated by respirometric and enzymologicalstudies. Simultaneous addition of malate, glutamate, and NAD+supported respiration in both types of Frankia, though at asmaller rate compared to the substrates NADH or 6-phosphogluconate.The saturating concentrations of malate and glutamate were alsomuch higher than with the other substrates. No respiration wassupported by succinate. Activity of the enzymes malate dehydrogenase(EC 1.1.1.37
EC]
) and glutamate oxaloacetate transaminase (EC 2.6.1.1
EC]
)was demonstrated in crude extracts from both types of symbioticFrankia. Their maximum rates were high enough to account forthe respiration of malate and glutamate. This respiration wasinhibited by mersalylic acid, an inhibitor of the dicarboxylateshuttle in mitochondria, but it was shown that inhibition ofrespiration could be due to a direct effect on the enzymes.We conclude that respiration of malate and glutamate is mostlikely mediated by malate dehydrogenase and glutamate oxaloacetatetransaminase, but no explicit evidence for or against the presenceof a dicarboxylate carrier was found. The utilization of respiratorysubstrates was largely similar in the two types of Frankia,except for some differences in maximum rates and cofactor dependency. Key words: Actinorhizal symbioses, Alnus, dicarboxylate shuttle, Frankia, reducing power, respiration |
