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Characterization of Alkylamine-Sensitive Site in α 2-macroglobulin
Richard P. Swenson and James Bryant Howard
Proceedings of the National Academy of Sciences of the United States of America
Vol. 76, No. 9 (Sep., 1979), pp. 4313-4316
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/70075
Page Count: 4
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Methylamine reacts with the plasma protease inhibitor, α 2-macroglobulin, to form an irreversible, covalent modification. Quantitation of the reaction indicates 3.9 ± (SD) 0.4 reactive sites per native tetrameric protein (Mr = 725,000) or one site per subunit. The reaction is selective and specific in that only 1 or 2 labeled peptides are observed on radioautography of peptide maps derived from [14C]methylamine-treated α 2-macroglobulin. A single chymotryptic peptide was isolated in 56% overall yield from the labeled protein. The peptide sequence by Edman degradation was found to be Gly-Cys-Gly-Glu-X-Asn-Met-(Val, Leu), in which X was the only radiolabeled phenylthiohydantoin derivative. Amino acid analysis and mass spectral analysis of the derivative suggests that X is γ -glutamylmethylamide. Because glutamic acid and glutamine residues do not normally react with alkylamines, this work presents presumptive evidence for an alternative activated center in selected proteins.
Proceedings of the National Academy of Sciences of the United States of America © 1979 National Academy of Sciences