Interaction of arylazido-beta-alanyl NAD+, a photoaffinity analogue of NAD+, with mitochondrial dihydronicotinamide adenine dinucleotide-ubiquinone reductase

N-arylazido-beta-alanyl-NAD+, a new NAD+ photoaffinity analogue. Synthesis and labeling of mitochondrial NADH dehydrogenase

N-Arylazido-beta-alanyl-NAD+ [N3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NAD+] has been prepared by alkaline phosphatase treatment of arylazido-beta-alanyl-NADP+ [N3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NADP+]. This NAD+ analogue was found to be a potent competitive inhibitor (Ki = 1.45 microM) with respect to NADH for the purified bovine heart mitochondrial NADH dehydrogenase (EC 1.6.99.3). The enzyme was irreversibly inhibited as well as covalently labeled by this analogue upon photoirradiation. A stoichiometry of 1.15 mol of N-arylazido-beta-alanyl-NAD+ bound/mol of enzyme, at 100% inactivation, was determined from incorporation studies using tritium-labeled analogue. Among the three subunits, 0.85 mol of the analogue was bound to the Mr = 51,000 subunit, and each of the two smaller subunits contained 0.15 mol of the analogue when the dehydrogenase was completely inhibited upon photolysis. Both the irreversible inactivation and the covalent incorporation could be prevented by the presence of NADH during photolysis. These results indicate that N-arylazido-beta-alanyl-NAD+ is an active-site-directed photoaffinity label for the mitochondrial NADH dehydrogenase, and are further evidence that the Mr = 51,000 subunit contains the NADH binding site. Previous studies using A-arylazido-beta-alanyl-NAD+ [A3'-O-(3-[N-(4-azido-2-nitrophenyl)amino]propionyl)NAD+] demonstrated that the NADH binding site is on the Mr = 51,000 subunit [Chen, S., & Guillory, R. J. (1981) J. Biol. Chem. 256, 8318-8323]. Results are also presented to show that N-arylazido-beta-alanyl-NAD+ binds the dehydrogenase in a more effective manner than A-arylazido-beta-alanyl-NAD+.

Studies of the ferricyanide reductase activities of the mitochondrial reduced nicotinamide adenine dinucleotide-ubiquinone reductase (complex I) utilizing arylazido-beta-alanyl NAD+ and arylazido-beta-alanyl NADP+

The NADH and NADPH ferricyanide reductase activities present in mitochondrial NADH-CoQ reductase preparations have been studied utilizing two photoaffinity pyridine nucleotide analogues: arylazido-beta-alanyl NAD+ (A3'-O-[3-[N-(4-azido-2-nitrophenyl)amino]propionyl]NAD+) and arylazido-beta-alanyl NADP+ (N3'-O-[3-[N-(4-azido-3-nitrophenyl)amino]propionyl]NADP+). For the NADH-K3Fe(CN)6 reductase activity, arylazido-beta-alanyl NAD+ was found to be, in the dark, a competitive inhibitor with respect to both NADH and K3Fe(CN)6 with Ki,app values of 9.7 and 15.5 microM, respectively. In comparison the NADP+ analogue exhibited weak noncompetitive inhibitor activity for this reaction against both substrates. Upon photoirradiation arylazido-beta-alanyl NAD+ inhibited NADH-K3Fe(CN)6 reductase up to 70% in the presence of a 25-fold molar excess of analogue over the enzyme concentration. This photodependent inhibition could be prevented by the presence, during irradiation, of the natural substrate NADH. In contrast complex kinetic results were obtained with studies of the effects of the pyridine nucleotide analogues of NADPH-K3Fe(CN)6 reductase activity in the dark. Photoirradiation of either analogue in the presence of the enzyme complex resulted in an activation of NADPH-dependent activity. The possibility that the NADPH-K3Fe(CN)6 reductase activity of complex I represents a summation of the combined ferricyanide reductase activity of the NADPH-NAD+ transhydrogenase and NADH oxidoreductase is suggested.

Photodependent incorporation of arylazido-beta-alanyl-NAD+ into the coenzyme binding site of yeast glyceraldehyde-3-phosphate dehydrogenase

Yeast glyceraldehyde-3-phosphate dehydrogenase was labeled in a photodependent reaction by the arylazido-beta-alanyl derivative of NAD+. This analogue was bound covalently to the enzyme and could be reduced in situ by the substrate glyceraldehyde-3-phosphate. That this derivative was bound to the active site in the proper orientation was shown by fluorescence experiments, from the retention of the enzymatic activity when the photolysis of the enzyme-analogue binary complex was carried out in the presence of NAD+. In the dark a non-photodependent competitive inhibition corresponding to a KI-value of 150 microM was observed. Thiol groups of the enzyme were not modified in the photolabeling reaction. Of the various arylazido-beta-alanyl nucleotide derivatives studied, the NADP+ derivative influenced the enzymatic activity to the greatest extent; this is probably due to an ionic bond between enzyme and nucleotide, in addition to the covalent bond of the photolytic reaction.