Study of UVA irradiation on hemoglobin in the presence of NADH.

Reduction of ferric methemoglobin (metHb) to its ferrous form is observed by short-time ultraviolet A (UVA) irradiation of metHb together with nicotinamide adenine dinucleotide (NADH). And, severely structural destruction of metHb occurs when long-time UVA irradiation is exerted. However, neither reduction nor destruction can be observed in the absence of NADH under otherwise the same experimental conditions. Accordingly, the O2-binding ability of the protein increases by short-time UVA irradiation of metHb together with NADH, which corresponds with the reduction of metHb, while it decreases by long-time UVA irradiation, which corresponds with the structural destruction. Besides, it is found that the reduction reaction and the conformational destruction proceed more rapidly with higher concentrations of NADH.