Characterization of the glycogen synthase D found in liver of the adrenalectomized fasted rats

• Published in: Biochimica et biophysica acta Vol. 614; no. 2; pp. 328 - 338
• Main Authors: Tan, A W, Tan, A H, Nuttall, F Q
• Format: Journal Article
• Language: English
• Published: Netherlands 01.01.1980
• Subjects: Adrenalectomy; Animals; Cold Temperature; Fasting; Glycogen - pharmacology; Glycogen Synthase - isolation & purification; Glycogen Synthase - metabolism; Glycogen-Synthase-D Phosphatase - metabolism; Kinetics; Liver - enzymology; Male; Rabbits; Rats; Substrate Specificity
• ISSN: 0006-3002
• DOI: 10.1016/0005-2744(80)90222-3

We have previously shown that the synthase D (UDPglucose:glycogen 4-alpha-D-glucosyltransferase, EC 1.4.1.11) present in the liver of the adrenalectomized fasted rat was not converted to synthase I by synthase phosphatase from normal animals, suggesting the presence of a non-substrate form of synthase D (Tan, A.W.H. and Nuttall, F.Q. (1976) Biochim. Biophys. Acta 445, 118--130). The enzymatic properties of this synthase D have now been examined. Using optimal assay conditions, the total amount of synthase D activity in the adrenalectomized fasted rats was similar to that of normal fed rats when 1% glycogen was included in the homogenizing buffer. However, the two enzymes appeared to have different affinities for the substrate, UDPglucose and the modifier, glucose-6-P. The changes in kinetic properties were not due to differences in glycogen or to a dialyzable modifier in the extracts. Synthase D from adrenalectomized fasted and from normal fed rats was partially purified. After DEAE-cellulose chromatography, modification appeared to have occurred such that the enzyme from the adrenalectomized fasted rat had properties similar to that of the normal fed rat. The enzymes were cold-labile, had different properties from enzymes in the crude extract and they were both converted to synthase I by synthase phosphatase. We conclude from these studies that the phosphorylation site in the synthase is in a flexible region of the protein. Changes in the ability of the synthase D to interact and be dephosphorylated by synthase phosphatase can occur readily in vivo and in vitro. The molecular basis for the modification remains unknown.