Effects of the Calvin cycle on nicotinamide adenine dinucleotide concentrations and redox balances of Xanthobacter flavus

Abstract

The levels of reduced and oxidized nicotinamide adenine dinucleotides were determined in Xanthobacter flavus during a transition from heterotrophic to autotrophic growth. Excess reducing equivalents are rapidly dissipated following induction of the Calvin cycle, indicating that the Calvin cycle serves as a sink for excess reducing equivalents. The physiological data support the conclusion previously derived from molecular studies in that expression of the Calvin cycle genes is controlled by the intracellular concentration of NADPH.

FIG. 1

(A) Activities of RuBisCO (○), phosphoglycerate kinase (PGK; ■), and formate dehydrogenase [FDH (NAD-dependent); ▴] of X. flavus growing on 5 mM gluconate. The results following addition of 20 mM formate and automatic titration with formic acid (25% [vol/vol]) at time zero) are shown. Enzyme activities are expressed in nanomoles per minute per milligram of protein. (B) NAD(H) (▾) and NADP(H) (▿) redox balance ([NAD(P)H]/[NAD(P)] + [NAD(P)H]) of X. flavus growing on 5 mM gluconate. The results before and after the addition of 20 mM formate and automatic titration with formic acid (25% [vol/vol]) at time zero are shown.

FIG. 2

Concentrations of NADH (A, □) and NADPH (A, ■) and total concentrations of NADH plus NAD⁺ (B, ○) and NADPH plus NADP⁺ (B, ●) following the addition of 20 mM formate to a culture growing on 5 mM gluconate at time zero.