Control of proteolysis in perifused rat hepatocytes

AbstractThe mechanism by means of which amino acids inhibit intrahepatic protein degradation has been studied in perifused rat hepatocytes. Proteolysis was extremely sensitive to inhibition by low concentrations of amino acids. A mixture of 0.5 mM leucine and 1–2 mM alanine, concentrations found in the portal vein of the rat after feeding, inhibited proteolysis to the same extent as a complete physiological mixture of amino acids. Inhibition by these two amino acids was accompanied by a rise in the intracellular concentrations of glutamate and aspartate, and was largely prevented by addition of glucagon, by addition of the transaminase inhibitor aminooxyacetate, or by omission of K+. Acceleration of proteolysis by K+ depletion was accompanied by a fall in intracellular glutamate caused by an increased rate of transport of this amino acid to the extracellular fluid. It is concluded that intracellular leucine, glutamate and aspartate are important elements in the control of hepatic protein degradation

Glucosylation of chimeric proteins in the cell wall of Saccharomyces cerevisiae

AbstractExtension of a reporter protein with the carboxyterminal thirty amino acids of the cell wall mannoprotein α-agglutinin of Saccharomyces cerevisiae resulted in incorporation of the chimeric protein in the cell wall. By Western analysis it was shown that the incorporated protein contained β-1,6-glucan similar to endogenous cell wall proteins, whereas excreted reporter protein was not glucosylated. This suggests that β-1,6-glucan is involved in anchoring mannoproteins in the cell wall