The Structure of a Calcium-binding Protein from Carp Muscle

We have determined the structure of one of the low molecular weight albumins of carp, using standard techniques of amino acid sequence analysis and heavy atom replacement crystallography. Originally we became interested in these so-called myogens or parvalbumins because of their unusual amino acid compositions—10% Phe and 20% Ala with little or no Trp, Tyr, Met, His, Cys or Arg (Konosu, Hamoir and Pechere, 1965). Subsequently it has been found that they have a high calcium-binding affinity (Pechere et al., 1971). These two characteristics suggest that the myogen to be described is analogous to troponin-A of mammalian and avian muscle (Ebashi et al., 1969; Greaser and Gergely, 1970; Drabikowski et al., 1971). Troponin-A mediates the effect of calcium released from the sarcoplasmic reticulum by the nervous impulse by reversing the inhibition of actomyosin contraction imposed by tropomyosin.