Initiation of ovalbumin synthesis in chicken oviduct magnum: Transient labeling of the NH2-terminus by methionine |
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Authors: | Chandan Prasad Alan Peterkofsky |
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Institution: | Laboratory of Biochemical Genetics, National Heart and Lung Institute, National Institutes of Health, Bethesda, Maryland 20014 USA |
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Abstract: | The incorporation of 35S]methionine into ovalbumin, a protein containing NH2-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 (P0, P1, and P2-containing 0, 1, and 2 moles of phosphate, respectively, per mole of ovalbumin). The kinetics of labeling of peaks P0 and P1 showed that the ratio of radioactivity in NH2-terminal methionine to total incorporation was greater at 2 min of labeling than at later times. The transient labeling of the NH2-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 NH2-terminal N-acetylglycine. |
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