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Chemical Evidence For Identical Subunits In L-asparaginase From Escherichia Coli B.
Published 1972 · Chemistry, Medicine
Abstract Application of four independent methods for cystine indicate that there are eight half-cystines per mole of Escherichia coli B asparaginase, consistent with a four subunit model with one intrachain disulfide link per subunit. Treatment with dinitrofluorobenzene showed only leucine as NH 2 -terminal amino acid; values of 3.17–3.9 moles of DNP-Leu per mole of asparaginase were obtained. Hydrazinolysis released tyrosine as the principal amino acid, 3.3 residues per mole of protein being obtained. Studies with the carboxyl modification technique of Hoare and Koshland ( Hoare, D. G., and Koshland, D. E. (1967) J. Biol. Chem. 242, 2447 ) showed that 61% of the side chain carboxyl groups are present as amide. Studies with carboxypeptidase A demonstrated the carboxyl terminal sequence to be -(Ile, Glu, Asn)-Phe-Ile-Gln-Tyr. The results obtained by preparing two-dimensional peptide maps of the tryptic digest of reduced, S -aminoethylated enzyme are also in agreement with a four subunit model in which the subunits are identical or nearly so.