To gain some insight into the mechanism by which red light-biosystem interaction occurs, an investigation was made of certain features of purified glutamate dehydrogenase from beef liver (E.C. 184.108.40.206.) irradiated with either an He-Ne laser (632.8 nm) or a red light-emitting diode (650+/-20 nm). In both cases the energy dose was 0.24 J cm-2. Significant changes in the glutamate dehydrogenase extinction coefficient measured at 275 nm, the capability of the enzyme to bind the reduced form of nicotinamide adenine dinucleotide (NADH), certain kinetic parameters, the pH and temperature dependence and the sensitivity to guanosine 5 triphosphate (GTP) and adenosine diphosphate (ADP) were found, probably due to the interaction of light with a protein domain containing a metal ion or ions. He-Ne laser and diode irradiation were found to differ with regard to their interaction with glutamate dehydrogenase. Interestingly, different effects were also found when an He-Ne laser and a non-coherent Xe=Hg lamp were used to irradiate glutamate dehydrogenase under the same experimental conditions. This confirms that non-coherent light at various power levels affects the isolated glutamate dehydrogenase.
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