Respiratory Enzyme Systems in Symbiotic Nitrogen Fixation

Abstract

The dehydrogenating properties of 4 strains of the root-nodule bacteria were studied by a modified Thunberg method in which the Evelyn electric photometer and specially designed Thunberg tubes were used to measure the kinetics of the reduction process. Dehydrogenase activity of the root-nodule bacteria occurs between pH 4 and 10 with optima in the alkaline range of pH 8-8.2. Substrates such as glucose and lactate possess 2 optima, suggesting the introduction of a secondary system with a higher pH optimum than the primary system. Simple compounds such as Na formate have but a single optimum. The optimum temp. for the activation of glucose by 3 of the strains investigated is about 45[degree] C; R. trifolii has a lower opt. of about 40[degree] C. The energy of activation for mannitol and sorbose by R. trifolii 209 is about 8,500 calories. Maltose, glucose, pyruvate, malate, fructose and xylose are placed in a group having a value of 10,000-12,500 calories; lactate possesses a high [mu] value of 14,500 cal. All 4 strains of rhizobia activate a large number of diverse organic compounds. There is some strain variation on the different substrates, but it is not consistently associated with either effectiveness or infectiveness of organism. KCN and Na pyrophosphate stimulate the action of the dehydrogenases studied. NaF is inhibitory only at a high conc. Na azide and Na iodoacetate are powerful inhibitors. In a conc. of 2/3 [image], both methyurethane and ethylurethane completely inhibit dehydrogenation of the 6 substrates investigated. Na malonate inhibits not only the succinic acid "center" but also that concerned in the activation of glucose, lactate and malate.