Inactivation of lactate dehydrogenase by UV radiation in the 300 nm wavelength region.

The effect of UV radiation on lactate dehydrogenase (LDH) was investigated. LDH from bovine heart was exposed to 3.6-18 kJ/m2 of ultraviolet (UV) radiation in the 300 nm wavelength region. The activity of LDH was observed to decrease as a function of the dosage of UV radiation. The inactivation of LDH was independent of exposure rate at constant dosage of UV radiation. The decrease of LDH activity caused by UV 300 nm radiation was coupled to a decrease of the maximal velocity (Vmax) while the Michaelis constant (Km) remained unchanged. The absorption spectrum of the LDH changed during exposure to UV radiation suggesting an alteration of tryptophan in the LDH molecule.