STUDIES ON THE SYNTHESIS OF PLASMA GLYCOLIPOPROTEIN AND HEPATIC SUB-CELLULAR GLYCOPROTEIN IN EARLY CHOLINE DEFICIENCY

Abstract

Impairment of glycoprotein synthesis in trichloroacetic acid insoluble and in residual protein (d > 1.21) fractions of plasma in early choline deficiency has been confirmed. Plasma lipoproteins of d < 1.006, 1.006–1.063, and 1.063–1.21 are also rapidly labelled after intraperitoneal injection of glucosamine-1-¹⁴C. In general, there was no difference in specific radioactivity of plasma glycolipoproteins between choline-supplemented rats and rats deprived of choline for 2 days during 180 min of incorporation.Incorporation of glucosamine-1-¹⁴C into microsomal glycoprotein is significantly impaired in early choline deficiency. Further sub-microsomal fractionation produced evidence that the site of impairment of glycoprotein synthesis is in the smooth microsome portion. These studies suggest that a decreased synthesis of glycoprotein(s) in liver-microsome smooth membrane and in the plasma residual fraction (d > 1.21) may represent an impairment of 'lipoprotein precursor protein' synthesis in early choline deficiency. An inhibition of this limiting step would possibly impair the rate of plasma lipoprotein synthesis, leading to the development of fatty liver in choline deficiency.