Adenosine Diphosphoglucose-Starch Glucosyltransferases from Developing Kernels of Waxy Maize

Abstract

MATERIALS AND METHODSTwo adenosine diphosphoglucose: a-, 4-glucan a-4-glucosyltransferases were extracted from kernels of waxy maize harvested 22 days after pollination and separated by gradient elution from a diethylaminoethyl-cellulose column. Both fractions could utilize amylopectin, amylose, glycogen, maltotriose and maltose as primers. The rate of glucose transfer from adenosine diphosphoglucose to rabbit liver glycogen of fraction II was 78% of the rate of glucose transfer to amylopectin, but with fraction I the rate of transfer of glucose to rabbit liver glycogen was 380% of that observed to amylopectin. Glucan synthesis in the absence of added primer was found in fraction I in the presence of 0.5 M sodium citrate and bovine serum albumin. The unprimed product was a methanol-precipitable glucan with principally a-1,4 linkages and some a-1,6 linkages, and its iodine spectrum was similar to that of amylopectin.Either sugar nucleotide transferases or phosphorylase could be involved in the initiation and synthesis of starch in higher plants (3,4,10,(13)(14)(15). Multiple forms of ADP-glucose:a-1,4-glucan a-4-glucosyltransferase have been separated from spinach leaves, one of which in the absence of added primer catalyzes the synthesis of a glucan with principally a-i ,4 linkages and some a-1 , 6 linkages (12). The unprimed activity was stimulated over 1000-fold by BSA3 and high concentrations of some salts (12). In maize kernels, Tsai and Nelson (15) have found evidence for the presence of multiple forms of phosphorylase, two forms of which are capable of synthesizing a polyglucan in the absence of added a-1 ,4 glucan primer.The present communication reports the existence of two forms of ADP-glucose:a-1 ,4-glucan a-4-glucosyltransferase (ADP-glucose-starch glucosyltransferase) in waxy maize, one of which can catalyze the formation of a polyglucose with properties similar to amylopectin in the absence of added primer. Rates of the unprimed reaction were up to eight times faster than the primed reaction at physiological concentrations of ADP-glucose.

Function and Characterization of Starch Synthase I Using Mutants in Rice

“…1A), consistent with the results obtained in maize endosperm (Ozbun et al, 1971;Cao et al, 2000) and rice endosperm (Tanaka and Akazawa, 1971). The primer dependence of these rice SS isozymes is identical to that of maize (Ozbun et al, 1971;Cao et al, 2000). SSI and SSIIIa are major enzymes in developing rice endosperm and the activity of SSI is higher than that of SSIIIa (Fig.…”

“…Nevertheless, some biochemical studies of SS isozymes expressed in Escherichia coli (Imparl-Radosevich et al, 1998Senoura et al, 2004) and analysis of partially purified SS isozymes from plant tissues (Baba et al, 1993;MuForster et al, 1996;Cao et al, 2000) have been reported. Two SS activity peaks, designated SSI and SSII, have been fractionated by anion-exchange chromatography from soluble extracts of maize (Zea mays; Ozbun et al, 1971;Boyer and Preiss, 1981) and rice (Oryza sativa; Tanaka and Akazawa, 1971) developing endosperm. The enzyme responsible for the SSI activity peak was purified and identified as the product of its cDNA in maize (Mu-Forster et al, 1996;Knight et al, 1998).…”

Multiple forms of starch synthetase in maize varieties as revealed by disc‐gel electrophoresis and activity staining

“…The sample buffer consisted of 35% sucrose, imidazolechloride pit 5.8, such that the final cone. of chloride was 0.24 M. The applied extracts usually contained about 0.02 IU/ml of starch synthetase activity [ 10] or about 2.5 mg]ml of protein. The n:nning buffer was I :riM dithiothreitol, 35 mM L-asparagine in 10% sucrose, adjusted to pH.…”

“…Another possibility is that synthetase and branching enzyme are present in the fast-moving bands as a twoenzyme complex. It may be noted that Preiss and coworkers [ 10] have obtained from waxy maize a starch ~'nthetase which yields an am¥1opectin,like molecule after incubation with ADPglucose in the absence of added pruner.…”

“…Recent studies of starch biosynthesis have been complicated by the findings of multiple fomas of starch synthetase which differ in their properties and which mere to vary in amount during the development of plant organs [4,[8][9][10][11][12]. One of the main impediments to more rapid progress in comparing the variety of synthetases in different plants, plant organs, subcellular organelles and at different stages of development, is a lack of a rapid screening technique applicable to minimum arp, gunts of relatively crude materiM.…”