Humus preparations extracted from forest litter and soils by treatment
with salt buffer solution were found to exhibit polyphenol oxidase ac
tivity. The enzyme is present as a complex with humic substances, to w
hich it is bound both by labile electrostatic bonds and by stronger bo
nds. The enzyme is most strongly bound by the humic acids of horizon A
l. The presence of clay minerals in the preparations suggested that th
ey are an important component of the active organomineral complexes.