The biosynthesis of rat serum albumin. Composition and properties of the intracellular precursor, proalbumin.

ment site for carbohydrate groups or otherwise aid the channeling of proalbumin along the cytoplasmic membranes toward the bloodstream, (b) mask an important binding site as does the NHderminal segment of trypsinogen, or (c) assure formation of correct tertiary structure as does the intercalated C-peptide of proinsulin.We have isolated proalbumin from rat liver in an amount sufficient to investigate its chemical and physical properties.We report herein the results of these investigations and their implications in the search for a role for proalbumin.' The abbreviations used are: TPCK, L-1-tosylamide-2-phenylethylchloromethyl ketone; TLCK, K-p-tosyl-L-lysine chloromethyl ketone; iPr2PF, diisopropyl fluorophosphate; PI.3O6.peptic fragment from rat albumin, approximately residues 1-306; PTH, phenylthiohydantoin; NaCl/P,, phosphate-buffered saline (0.1 M NaCl, 0.016 M Na2HP04, 0.0038 M NaHzP04, pH 7.4).