Inhibition and simulation of proteolytic enzyme activities by soil humic acids

Abstract

The effects of neutralized solutions of soil humic acids on the activities of a range of proteolytic enzymes and of tyrosinase have been measured. Humic acids inhibit carboxypeptidase A, chymotrypsin A, pronase, and trypsin activities, stimulate papain, ficin, subtilopeptidase A, and thermolysin activities, and had no effect on phaseolain and tyrosinase activities. Stimulation of papain and ficin activities is not due to formation of metal ion-humic acid complexes. Inhibition of trypsin activity and stimulation of papain activity increased with increasing molecular weight of the humic acid. However, humic acid fractions of varying molecular weights had similar effects on the magnitude of inhibition of pronase and carboxypeptidase A activities. Polycondensates derived from p-benzoquinone and catechol influenced enzyme activity in the same way as humic acids, although the order of their relative effectiveness changed with different enzymes. Polyacrylate preparations were the most effective inhibitors of trypsin activity but had no effect on papain and ficin activities.