INHIBITION OF PALMITO POLYPHENOLOXIDASE BY HALIDE SALTS

The inhibitory properties of halide salts on palmito polyphencloxidase (PPO) are described. Halide salts have the same inhibitory effect on the two forms of palmito PPO separated by hydrophobic chromatography. Fluoride and chloride ions showed a non-competitive, mixed type inhibi tion while bromide and iodide ions were found to be non-competitive in hibitors. A study of the K-i for the different halide salts showed tha t the smaller F- ion is a stronger inhibitor than I- and Br- and that Cl- has the highest K-i value. This suggests that the active site of t he palmito PPO is not easily accessible. The inhibition by chloride an d fluoride ion was found to be pH-dependent. The inhibitory effects of these ions increased with a decrease in pH. It is suggested that hali de ions (X) could bind to either the protonated Enzyme (EH) or the pro tonated substrate-enzyme complex (EHS) to yield inactive forms EHX and EHSX, respectively.