Kinetic behaviour of a repressible acid phosphatase from the yeast Yarrowia lipolytica: a comparative study between the solubilized enzyme, the enzyme bound to cell-wall fragments and the enzyme bound to intact cells

Abstract

(1) The substrate specificities and types of inhibitors of a repressible acid phosphatase from the yeast Yarrowia lipolytica as solubilized enzyme, enzyme bound to cell-wall fragments and enzyme bound to the intact cell were found to be essentially the same. (2) A similar pattern for the activation of the enzymatic activity by ionic strength was found for solubilized enzyme, the enzyme in cell-wall fragments and the enzyme in intact cells. (3) υ-[S] studies with all three locations of the enzyme revealed non-linear Eadie-Hofstee plots with concave-up curves of the negative cooperativity type; these were correctly fitted with a rate equation of 2:2 degree polynomial quotient. In all cases, the same behaviour was obtained and no new kinetic properties were observed when the enzyme was bound to the cell-wall matrix with respect to the solubilized enzyme. (4) Inhibition by phosphate was characterized for the three locations of the enzyme by υ-[I] and υ-[S] studies. The same pattern of partial inhibition and non-Michaelian inhibition of ‘non-competitive’ nature was observed for all three forms. (5) The above results are interpreted in terres of the hypothesis that the cell wall of Y. lipolytica has a slight negative charge but behaves as a permeable matrix that does not lead to novel characteristics regarding the catalytic and regulatory properties shown by the enzyme molecule in free solution.