PHOTOMODULATION OF GLUTAMATE-DEHYDROGENASE PROPERTIES BY RED-LIGHT

To gain some insight into the mechanism by which red light-biosystem i nteraction occurs, an investigation was made of certain features of pu rified glutamate dehydrogenase from beef liver (E.C. 1.4.1.3.) irradia ted with either an He-Ne laser (632.8 nm) or a red light-emitting diod e (650+/-20 nm). In both cases the energy dose was 0.24 J cm-2. Signif icant changes in the glutamate dehydrogenase extinction coefficient me asured at 275 nm, the capability of the enzyme to bind the reduced for m of nicotinamide adenine dinucleotide (NADH), certain kinetic paramet ers, the pH and temperature dependence and the sensitivity to guanosin e 5 triphosphate (GTP) and adenosine diphosphate (ADP) were found, pro bably 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 a nd a non-coherent Xe=Hg lamp were used to irradiate glutamate dehydrog enase under the same experimental conditions. This confirms that non-c oherent light at various power levels affects the isolated glutamate d ehydrogenase.