In vitro synthesis of α-lactalbumin and β-lactoglobulin by microsomes and bound polyribosomes from the mammary gland of lactating sheep

Abstract 1. Synthesis of α-lactalbumin and β-lactoglobulin has been carried out in vitro by cell-free systems consisting of microsomes or bound polyribosomes derived from the mammary gland of the lactating ewe. 2. The two proteins labelled with 14 C and synthesized in vitro have been identified by; (a) their behaviour on chromatography with CM-cellulose and Sephadex G-100 columns and on electrophoresis in polyacrylamide gel: (b) their antigenic properties: (c) their molecular weights, determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate; (d) the number of peptides produced by tryptic hydrolysis of β-[ 14 C]lactoglobulin and their chromatographic and electrophoretic properties. 3. The distribution of the radioactivity between the peptides resulting from tryptic hydrolysis of β-lactoglobulin and the determination of the radioactivity of the N-terminal amino acid suggest that most of the radioactive amino acids incorporated in vitro into β-lactoglobulin correspond to the completion of peptide chains which began in vivo .