EFFECT OF TEMPERATURE AND PRESSURE ON YEAST INVERTASE STABILITY - A KINETIC AND CONFORMATIONAL STUDY

Kinetics of the temperature- or pressure-induced denaturation of inver tase from Saccharomyces cerevisiae were obtained in the temperature ra nge 45-70 degrees C and in the pressure range 500-650 MPa. The investi gation was done by measuring the residual activities after cooling or pressure release and the intrinsic fluorescence of aromatic amino-acid s (tyrosine and tryptophan) upon excitation at 277 nm. The residual ac tivity decreased exponentially as a function of time incubation accord ing to a biphasic model either with pressure or temperature, whereas t he fluorescence emission indicated a difference between these two para meters. When the enzyme was subjected to thermal treatment, the fluore scence of tyrosine and tryptophan decreased slowly, while after high-p ressure treatment, these aromatic residues become more exposed to the aqueous solvent during unfolding, giving rise to a large decrease in f luorescence in the 330-340 nm region. Moreover, in the latter case, an enhancement of light scattering intensity showed changes in protein-p rotein interactions.