An alpha-glucose-1-phosphate phosphodiesterase is present in rat liver cytosol

Journal Article · Tue Dec 05 00:00:00 EST 1989 · Journal of Biological Chemistry; (USA)

OSTI ID:5085649

Srisomsap, C; Richardson, K L; Jay, J C; Marchase, R B ^[1]

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1. Univ. of Alabama, Birmingham (USA)

UDP-glucose:glycoprotein glucose-1-phosphotransferase (Glc-phosphotransferase) catalyzes the transfer of alpha-Glc-1-P from UDP-Glc to mannose residues on acceptor glycoproteins. The predominant acceptor for this transfer in both mammalian cells and Paramecium is a cytoplasmic glycoprotein of 62-63 kDa. When cytoplasmic proteins from rat liver were fractionated by preparative isoelectric focusing following incubation of a liver homogenate with the 35S-labeled phosphorothioate analogue of UDP-Glc ((beta-35S)UDP-Glc), the acceptor was found to have a pI of about 6.0. This fraction, when not labeled prior to the focusing, became very heavily labeled when mixed with (beta-35S). UDP-Glc and intact liver microsomes, a rich source of the Glc-phosphotransferase. In addition, it was observed that the isoelectric fractions of the cytosol having pI values of 2-3.2 contained a degradative activity, alpha-Glc-1-P phosphodiesterase, that was capable of removing alpha-Glc-1-P, monitored through radioactive labeling both in the sugar and the phosphate, as an intact unit from the 62-kDa acceptor. Identification of the product of this cleavage was substantiated by its partial transformation to UDP-Glc in the presence of UTP and UDP-Glc pyrophosphorylase. The alpha-Glc-1-P phosphodiesterase had a pH optimum of 7.5 and was not effectively inhibited by any of the potential biochemical inhibitors that were tested. Specificity for the Glc-alpha-1-P-6-Man diester was suggested by the diesterase's inability to degrade UDP-Glc or glucosylphosphoryldolichol. This enzyme may be important in the regulation of secretion since the alpha-Glc-1-P present on the 62-kDa phosphoglycoprotein appears to be removed and then rapidly replaced in response to secretagogue.

• OSTI ID: 5085649
• Journal Information: Journal of Biological Chemistry; (USA), Vol. 264:34; ISSN 0021-9258
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
PHOSPHODIESTERASES
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AUTORADIOGRAPHY
GLUCOSE
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PHOSPHOTRANSFERASES
RATS
SUBSTRATES
SULFUR 35
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URIDINE
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FUNCTIONS
GLANDS
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HYDROGEN COMPOUNDS
HYDROLASES
HYDROXY COMPOUNDS
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LIGHT NUCLEI
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MONOSACCHARIDES
NUCLEI
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ORGANS
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550201* - Biochemistry- Tracer Techniques