ABSTRACT
In crude particulate fractions isolated from pea (Pisum sativum) cotyledons, the transfer of radioactivity from GDP-[(14)C]mannose to glycolipid appears to be preferentially stimulated by Mn(2+) while the transfer to lipid-free residue is enhanced by Mg(2+). In contrast, the transfer of radioactivity from UDP-N-acetyl-[(14)C]glucosamine to glycolipid shows preferential stimulation by Mg(2+) while the transfer to lipid-free residue prefers Mn(2+). These results are accounted for by the differential stimulation by Mg(2+) and Mn(2+) of glycosyl transferases associated with subcellular membranes which were separated by isopycnic sucrose density centrifugation.
ABSTRACT
Particulate preparations from developing cotyledons of Pisum sativum L. cv. Burpeeana catalyze glycosyl transfer from UDP-[(14)C]N-acetylglucosamine and GDP-[(14)C]mannose. Radioactivity is transferred to lipid components soluble in chloroform-methanol (2:1) and chloroform-methanol-water (1:1:0.3) and into a water-insoluble and lipid-free residue.The chloroform-methanol-soluble component formed from GDP-[(14)C]mannose appears to be a mannosyl lipid, whereas the chloroform-methanol-water-soluble fraction is probably a mixed oligosaccharide-lipid containing N-acetylglucosamine and mannose residues. The chloroform-methanol-soluble component formed from UDP-[(14)C]N-acetylglucosamine appears to be N,N'-diacetylchitibiosyl lipid, which may be incorporated with mannose to form the chloroform-methanol-water-soluble mixed oligosaccharide lipid.The oligosaccharide lipid appears to function as a precursor for the transfer of the oligosaccharide to the peptide moiety in the formation of the glycoproteins. The bulk of the radioactivity, arising from UDP-[(14)C]N-acetylglucosamine, incorporated into the insoluble residue, is associated with glycoprotein. In contrast only a small percentage of radioactivity in the insoluble residue, arising from GDP-[(14)C]mannose incorporation, appears to be associated with glycoprotein. The majority of the radioactivity found in the residue fraction labeled from GDP-[(14)C]mannose appears to be associated with oligomannosyl residues.
ABSTRACT
Secretion-the outward movement of molecules across the plasmalemma-of alpha-amylase by barley (Hordeum vulgare L. cv. Himalaya) aleurone layers is an energy-dependent process that is not directly dependent upon protein synthesis or RNA synthesis and does not appear to be under the direct control of gibberellic acid or abscisic acid. Release-the movement of the secreted alpha-amylase molecules through the walls into the surrounding medium-is apparently diffusion limited and is markedly dependent upon the presence of ions.
