Studies on potato tuber phosphorylase catalyzed reaction in the absence of an exogenous acceptor: II. Characterization of the reaction product

• Published in: Archives of biochemistry and biophysics Vol. 212; no. 2; pp. 537 - 545
• Main Authors: Sivak, Mirta N., Tandecarz, Juana S., Cardini, Carlos E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 1981
• Subjects: Carbon Radioisotopes; Centrifugation, Density Gradient; Chromatography, Affinity; Electrophoresis, Polyacrylamide Gel; Glucans - isolation & purification; Glucosephosphates - metabolism; Glycoproteins - isolation & purification; Isoenzymes - isolation & purification; Isoenzymes - metabolism; Molecular Weight; Phosphorylases - metabolism; Plants - enzymology
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(81)90397-0

Incubation of potato tuber phophorylase II with [ 14C]glucose 1-phosphate in the absence of an exogenous acceptor results in the synthesis of a radioactive product, presumably a protein-bound glucan. The carbohydrate moiety of this product was shown to consist of long α-1,4-glucosidic chains. The enzyme itself was originally assumed to be the first glucosyl acceptor in the unprimed reaction. However, as judged by urea-sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the radioactive product is rather resistant to proteolysis and is smaller in size than phosphorylase II. These data are in agreement with those obtained by sucrose density gradient centrifugation and molecular-weight estimation of native products. Thus, some kind of processing postglucosylation has to be proposed to account for the observed decrease in molecular weight. One cannot overlook the probable presence of a low-molecular-weight protein acceptor which copurifies along with phosphorylase II and whose separation from the enzyme can only be achieved upon glucosylation. On the other hand, protein was also found to be present in amylose from potato starch grains. It is therefore suggested that this finding might become an additional evidence of a common biosynthetic pathway for α-1,4-glucans from a precursor protein.