The effect of regucalcin, which is a regulatory protein in Ca2+ signaling, on protein synthesis in regenerating rat liver was investigated. Protein synthesis was assayed in a reaction mixture containing the 5500 g supernatant fraction in the presence of [3H]leucine. The presence of anti-regucalcin monoclonal antibody (100 and 150 ng/ml) in the reaction mixture caused a significant elevation of in vitro protein synthesis. This elevation was completely prevented by the addition of regucalcin (1.0 microM). Regenerating liver after partial hepatectomy (HPX) induced a significant increase in protein synthesis. This increase was significantly enhanced by the presence of anti-regucalcin monoclonal antibody (100 ng/ ml). This enhancement was remarkable at 24 and 48 h after HPX. [3H]Leucyl-tRNA synthetase activity in the 105000 g supernatant fraction (cytosol) of the liver homogenate from normal rats was significantly raised by the presence of antibody (100 and 150 ng/ml) in the enzyme reaction mixture. Regenerating liver caused a significant elevation of the enzyme activity at 24, 48, and 72 h after HPX. This elevating was significantly enhanced in the presence of antibody (100 ng/ml). The present study suggests that endogenous regucalcin has a suppressive effect on the enhancement of protein synthesis in regenerating rat liver with a proliferative cells.

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