A specific enzyme hydrolyzing 6-O(4-O)-indole-3-ylacetyl-β-d-glucose in immature kernels of Zea mays

The purification of 6-O(4-O)-indole-3-ylacetyl-β-d-glucose (IAGlc) hydrolase from immature kernels of maize (Zea mays) was undertaken to separate this enzyme from 1-O-IAGlc hydrolase and β-glucosidase. Partially purified 6-O(4-O)-IAGlc hydrolase was found to be the specific enzyme catalyzing hydrolysis of stable esters of IAA and glucose. Among a range of ester conjugates tested as substrates, only 6-O(4-O)-IAA-glucose and IBA-glucose isomers were effectively hydrolyzed. No activity against p-nitrophenyl-β-d-glucopyranoside, a synthetic substrate for β-glucosidase, was detected in the enzyme preparation. The enzyme is probably involved in the regulation of the IAA levels by the target release of free auxin from ester-linked conjugates, its inactive storage forms.