Enzymic synthesis of indol-3-ylacetyl-myo-inositol galactoside

Abstract
Extracts of immature kernels of Zea mays catalyzed the synthesis of [the growth hormone] indol-3-ylacetyl-myo-inositol galactoside from indol-3-ylacetyl-myo-inositol and UDP-galactose. Addition of 2-mercaptoethanol was required for stability of the catalytic activity during dialysis. The enzyme could be fractionated with (NH4)2SO4, and 55% of the activity was recovered in the 30 to 60%-saturation fraction. The product of the reaction contained radioactivity from UDP-[U-14C]galactose and was identified as indol-3-ylacetyl-myo-inositol galactoside by gas chromatography-mass spectometry. A UDP-galactose:indol-3-ylacetyl-myo-inositol galactosyltransferase (indol-3-ylacetyl-myo-inositol galactoside synthase) is present in developing kernels of Z. mays. The description of this enzyme in the synthesis of indol-3-ylacetylglucose and indol-3-ylacetyl-myo-inositol now provides mechanisms for the biosynthesis of 1/2 of the low-MW esters of IAA in Z. mays.