Increased stability and catalytic efficiency of yeast hexokinase upon interaction with zwitterionic micelles. Kinetics and conformational studies

The effect of ligands (glucose, ATP and Mg2+) and zwitterionic micelles of lysophosphatidylcholine (LPC) or N-hexadecyl-N,N-dimethyl-3-ammonium propan esulfonate (HPS) in the yeast hexokinase (HK) stability was studied at 35 d egrees C. The thermal inactivation kinetics followed one-exponential decay. The effect of ligands bn protecting the enzyme against inactivation follow ed the order: glucose > glucose/Mg2+ > ATP/Mg2+ congruent to Mg2+ congruent to buffer only. Both LPC and HPS micelles increased the enzyme stability o nly when the incubation medium contained glucose or glucose/Mg2+, suggestin g that the protein conformation is a key prerequisite for the enzyme-micell e interaction to take place. This enzyme-micelle interaction resulted in an increased catalytic efficiency (with a decrease in K-m for ATP and increas e in V-max as well as in changes on the tertiary (intrinsic fluorescence) s tructure of the yeast hexokinase.