Vol. 54, No. 2, 1973 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS A SYNTHETIC TRIPEPTIDE WHICH INCREASES SURVIVAL OF NORMAL LIVER CELLS, AND STIMULATES GROWTH IN HEPATOMA CELLS L. Pickart, L. Thayer and M. M. Thaler Department of Pediatrics, University of California, San Francisco 94143 Received July 30, 1973 SUMMARY: A synthetic peptide with a structure analogous to a growth promoting human serum tripeptide was found to possess activities which, at nanomolar concentrations, increased the survival of normal hepatocytes from regenerating rat liver and which enhanced growth of a line of cultured hepatoma cells. The synthetic tripeptide (glycyl-histidyl-lysine) also stimulated the incorporation of labeled uridine and thymidine into trichloroacetic acid precipitable material. INTRODUCTION: We have recently identified a small peptide in human serum which enhances macromolecular synthesis in rat liver cells and in rat hepatoma cells in culture. (1) Nanogram amounts of this native factor added to growth-limiting medium caused prolonged survival of hepatocytes and enchanced growth of a cultured line of rat hepatoma cells. Amino acid analyses suggested that the active factor was a tripeptide formed by glycine, histidine and lysine. We are reporting that synthetic glycyl-histidyl-lysine has similar biological properties to the native factor. MATERIALS AND METHODS: All necessary reagents for synthesis of the tripeptide were purchased from Sigma Chemical Co., St. Louis. The synthetic procedure was the solid phase method of Stewart and Young (2) as modified for deblocking by Gutte and Merrifield (3). BOC blocking groups were removed with 30% trifluoroacetic acid (TFA) in CH2 C12. The imidazole side chain of histidine was left unprotected. Copyright @ I973 by Academic Press, Inc. All rights of‘ reproduction in arty Jkrrn reserved. 562