Multiple forms of starch branching enzyme of maize: evidence for independent genetic control

PuriEication of starch branching enzymes from kernels of two nonlinked mutants of maize, sugary and amylose-extender, showed the basis of the two mutations to be associated with branching enzymes I and IIb, respectively. Branching enzyme I from sugary kernels purified as nonmutant branching enzyme I, but had an altered pattern of activity when amylose was used as a substrate. In addition to the typical fall in absorbance at high wavelengths (550-700 nm)of the amylose-iodine complex, branching of amylose by sugary branching enzyme I caused an increase in absorbance at low wavelengths (400-550 nm). Branching enzyme IIb was undetected in extracts of amylose-extender kernels, while branching enzymes I and IIa appeared unaltered. Low umprimed starch synthase activity was also observed in DEAE-cellulose fractions of amyloseextender maize, but this activity was regenerated by the addition of any branching enzyme