The Effect of Temperature, Enzymic Complex Formation on the Room-Temperature Phosphorescence of Tryptophan Residue in Horse Liver Alcohol Dehydrogenase

Abstract

The binding of NAD, NADH and ADPR to LADH was accompanied by different temperature dependence of the phosphorescence decay rate of the tryptophan residue buried within the protein over the temperature range 0 to 30°C in aqueous solution. As a result of thermally induced transition with a hysteresis cycle in the response to temperature, the Arrhenius curves of the phosphorescence decay rate for NAD– and ADPR–EtOH–LADH complexes were overlapped with those for NADH– and ADPR–LADH complexes, respectively. The typical value of the decay rate at 0°C for the samples distributed at intervals over the range 20–1.5 sec⁻¹ suggesting that the degree of stability of LADH dimer decreased in the order NADH–>NAD–>EtOH–>ADPR–LADH. In order to explain those results by thermal fluctuation process, a model for the conformation changes of the micro-environment around the residue is presented.