L-PHENYLALANINE INHIBITION OF RAT INTESTINAL ALKALINE PHOSPHATASE - A HOMOSTERIC PHENOMENON

Evidence was sought to characterize further the nature of the uncompetitive stereospecific inhibition of rat intestinal alkaline phosphatase by l-phenylalanine. That it is nonallosteric is clear from (1) the hyperbolic curves relating inhibition as a function of inhibitor or substrate concentration; (2) the persistence of inhibition after the tertiary structure of the enzyme protein molecule had been altered by heat denaturation, papain digestion and treatment with urea or stilbestrol; (3) the relatively low entropy change of -6.7 entropy units per mole; (4) the figure of unity for n, the number of l-phenylalanine molecules which combine with one molecule of enzyme. However, this inhibition may represent an example of McElroy's homosteric transition since the extent of l-phenylalanine inhibition decreases with an increase in temperature and the optimal temperature for maximal velocity is raised in digests containing l-phenylalanine. © 1968.