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  • Title: Primary structures of the alpha-crystallin A chains of twenty-eight mammalian species, chicken and frog.
    Author: de Jong WW, Zweers A, Versteeg M, Nuy-Terwindt EC.
    Journal: Eur J Biochem; 1984 May 15; 141(1):131-40. PubMed ID: 6723655.
    Abstract:
    The amino acid sequences of the alpha-crystallin A chains of 28 mammalian species, representing 14 different orders, have been analyzed, mainly on the basis of amino acid compositions of the composing peptides. The alpha A sequences of chicken and a frog have been completely determined by Edman degradation. A method is described to transport eye lenses, to be used for protein sequence studies, at ambient temperature in a solution of guanidine . HCl. The number of cysteine residues in different alpha A chains could be determined by alkaline urea gel electrophoresis after aminoethylation . In some cases the alpha A chains have been isolated from total lens extracts in a single ion-exchange chromatographic step. The average rate of substitutions in the evolution of the alpha A chains is moderately slow, approximately 3 amino acid substitutions per 100 residues in 100 million years, but varies considerably in different lineages. Substitutions involving changes in charge are strongly underrepresented; the alpha A chains tend to keep their net charge constant throughout evolution. Analysis of the types of substitutions suggests a directional trend leading to an increase in functional density of alpha A in the course of evolution.
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