Fluorescence quenching of liver alcohol dehydrogenase by acrylamide

Abstract

The quenching of the fluorescence of liver alcohol dehydrogenase by acrylamide was studied as a function of excitation and emission wavelength. Downward curving Stern-Volmer plots are found, providing further support for the notion that Trp-15 of the protein is surface exposed and that Trp-314 is extensively buried within the protein. The acrylamide quenching of the binary complex formed between the protein and NAD+ was also studied. The quenching pattern in this case is found to be complicated due to the interaction of acrylamide with the binary complex. Independent evidence for the fact that acrylamide binds to the binary complex is obtained from enzyme inhibition studies and from NAD+ binding studies showing acrylamide to bind with positive cooperativity with respect to the coenzyme. When the interaction of acrylamide with the binary complex is taken into consideration, however, the quenching data can be interpreted as indicating that the binding of NAD+ to the protein does not induce a conformational change that leads to the exposure of Trp-314.