Alanine Dehydrogenase from Bacteroids and Free Living Cells of Rhizobium japonicum

Abstract

Abstract Alanine dehydrogenase (E.C. 1.4.1.1.) from nitrogenase repressed free living cells of Rhizobium japonicum 61-A-101 was purified 370 fold to a specific activity o f 30.4 (μmol pyruvate · min-1 · mg protein-1. The same enzyme from effective bacteroids from nodules of Glycine max var. Mandarin, infected with the same strain was purified 150 fold to a specific activity of 35 units. The enzyme from both preparations was identical in the molecular weight of about 168 kD with four identical subunits of 42 kD. The alanine dehydrogenase is, therefore, different from the same enzyme from Bacillus subtilis (molecular weight 228 kD) and from Anabaena cylindrica (molec­ ular weight 270 kD). The Kᴍ data for the enzyme from Rhizobium japonicum are: 4.7 mmol/l for NH+ 4 0.68 mmol/l for pyruvate and 44 μmol/l for NADH. Specific activity of the enzyme in total cell extracts from eight other strains of Rhizobium japonicum (3 effective strains, 5 ineffective strains) was only 20 to 30% o f the activity with strain 61-A-101. No correlation between alanine dehydrogenase activity and nitrogenase activity in these other eight strains was observed. The function of alanine dehydrogenase in Rhizobium japonicum in ammonium assimilation and cell wall differentiation is discussed.