Involvement of a lipid-linked intermediate in the transfer of galactose from UDP [14C]galactose to exogenous protein in castor bean endosperm homogenates |
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Authors: | R B Mellor J M Lord |
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Institution: | (1) Postgraduate School of Biological Sciences, University of Bradford, BD7 1DP Bradford, U.K.;(2) Present address: School of Biological Sciences, The University, DD1 4HN Dundee, U.K. |
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Abstract: | A crude organelle preparation from germinating castor bean endosperm catalysed the incorporation of galactose from UDP14C]galactose into chloroform/methanol (2:1)-soluble glactolipids. At least two galactolipids were formed. Most of the 14C]galactose was present in a galactolipid synthesized by the microsomal membranes, the remainder was present in a second galactolipid synthesized by other cellular membranes, possibly Golgi-derived. The addition of asialo-agalacto-fetuin reduced incorporation of 14C]galactose into the microsomal galactolipid with a concomitant increase in microsomal 14C]galactoprotein. Asialo-agalacto-fetuin did not affect galactolipid or galactoprotein synthesis by nonmicrosomal fractions. The results suggest that the endoplasmic reticulum is a major site of protein galactosylation in castor bean endosperm cells, and that galactose transfer from UDP-galactose to protein occurs via a lipid-linked intermediate.Abbreviations ER
endoplasmic reticulum
- ASGF
asialoagalacto-fetuin
- IDPase
inosine diphosphatase
- TCA
trichloroacetic acid |
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Keywords: | Endoplasmic reticulum Golgi-galactolipid-galactoprotein Ricinus |
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