Initiation of ovalbumin synthesis in chicken oviduct magnum: Transient labeling of the NH 2-terminus by methionine

Abstract

The incorporation of [ 35S]methionine into ovalbumin, a protein containing NH 2-terminal N-acetylglycine, has been studied in chicken oviduct magnum cells. The purification of [ 35S]methionine-labeled ovalbumin from total oviduct proteins was accomplished by dialysis of a crude extract at pH 3.6 followed by chromatography on carboxymethyl cellulose. The radioactive ovalbumin eluted from the column in three peaks (P 0, P 1, and P 2-containing 0, 1, and 2 moles of phosphate, respectively, per mole of ovalbumin). The kinetics of labeling of peaks P 0 and P 1 showed that the ratio of radioactivity in NH 2-terminal methionine to total incorporation was greater at 2 min of labeling than at later times. The transient labeling of the NH 2-terminus of ovalbumin with methionine indicates that methionine is the initiator amino acid for the synthesis of this protein, which in its mature form contains NH 2-terminal N-acetylglycine.