Nonenzymic hydrogen transfer between reduced and oxidized pyridine nucleotides

Area of Science:

• Biochemistry
• Enzymology
• Chemical Kinetics

Background:

• Nicotinamide adenine dinucleotide (NAD) and its derivatives are crucial coenzymes in biological redox reactions.
• Understanding the nonenzymic reactions of these coenzymes is vital for elucidating metabolic pathways and developing biochemical assays.

Purpose of the Study:

• To investigate the nonenzymic hydrogen transfer between reduced nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADP+), and between NADPH and NAD+.
• To identify the specific site of hydrogen transfer on the pyridine ring of these coenzymes.

Main Methods:

• Incubation of mixtures containing NADH/NADP+ or NADPH/NAD+.
• Assay of hydrogen transfer by measuring the formation of NADPH and NADH using specific enzymes: glutathione reductase and lactate dehydrogenase, respectively.
• Characterization of the enzymic activity of the resulting products.

Main Results:

• Demonstrated a steady, nonenzymic transfer of hydrogen from reduced pyridine nucleotides (NADH, NADPH) to their oxidized counterparts (NADP+, NAD+).
• Confirmed that the hydrogen transfer occurs specifically to the C-4 position of the pyridine ring in NADP+ and NAD+.
• The products of the nonenzymic reaction retained complete enzymic activity.

Conclusions:

• The C-4 position of the pyridine ring is the specific site for nonenzymic hydrogen transfer in NAD(P)+/NAD(P)H systems.
• Nonenzymic hydrogen transfer reactions contribute to the redox chemistry of pyridine nucleotides.
• These findings have implications for understanding pyridine nucleotide metabolism and designing enzymatic assays.