Hoppe-Seyler's Z. Physiol. Chem. Bd. 364, S. 439-445, April 1983 Serum Apolipoprotein AI Synthesis in Rat Hepatocytes and its Secretion as Proform Wilhelm STOFFEL, Christoph BODE and Klaus KNYRIM Institut für Physiologische Chemie der Universität Köln (Received 28 December 1982) Summary: Rat hepatocytes in monolayer or Suspension culture synthesize serum lipoprotein AI. It is secreted into the serum-free culture medium. Synthesis and secretion processes were studied in the presence of radiolabelled amino acids. The synthesis product of the hepatocytes and the secretion product from the medium were isolated by immunoprecipitation with a mono- specific rabbit antiserum against rat apolipo- protein AI. The intracellular and secreted products were homogeneous and identical in polyacrylamide gel electrophoresis but had reduced electro- phoretic mobility as compared to native apo- lipoprotein AI. They were submitted to auto- mated Edman degradation. They were present in their proform, the N-terminus of which is extend- ed by a hexapeptide. In the presence of rat serum the proform is proteolytically transformed into the mature form of apolipoprotein AI. Synthese des Apolipoproteins AI in Ratten-Hepatozyten und seine Sekretion Zusammenfassung: Rattenleberzellen in Mono- layer-Kulturen oder in Suspension synthetisie- ren Apolipoprotein AI und sezernieren es in das Medium. Die Synthese wurde in Gegenwart von radioak- tiven Aminosäuren durchgeführt. Mit Hilfe von monospezifischen Antikörpern gegen Ratten- Apolipoprotein AI wurden das Syntheseprodukt aus den Hepatozyten und das Sekretionsprodukt aus dem serumfreien Medium isoliert. Beide radio- aktiven Apoproteine wurden dem Edman-Abbau unterworfen. Ihre N-terminalen Sequenzen waren identisch. Hepatozyten sezernieren das Apolipoprotein AI in seiner Pro-Form in serumfreies Medium. Der N-Terminus des Sekretionsproduktes ist um ein Hexapeptid extendiert. In Gegenwart von Rattenserum wird die Pro- Form proteolytisch in die reife Form des Apo- lipoproteins AI umgewandelt. Abbreviations: Apo AI, All = apolipoprotein AI, All of serum high-density lipoproteins, HDL = serum high-density lipoprotein, KIE = kallikrein inhibitor units. 0018-4888/83/0364-0439$02.00 © Copyright by Walter de Gruyter & Co · Berlin · New York Brought to you by | New York University Bobst Lib Authenticated Download Date | 5/30/15 4:03