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Preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis has been used to purify digitonin extracts of rod outer segments of squid retinas. Besides rhodopsin the extracts contained small amounts of seven or eight contaminating proteins plus a light-stable pink-purple pigment identified as ommin. Reproducible amino acid analyses were obtained from separate purified preparations of opsin, the protein component of the rhodopsin molecule. One NH2-terminal glycine per mole of retinaldehyde chromophores was detected. Relative mobility of the opsin on analytical sodium dodecyl sulfate polyacrylamide gels indicated a single peptide unit with a molecular weight of approximately 49,000.
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Frances M. Hagins (1973) studied this question.
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