Abstract
EARLIER studies of the location of the single cysteine residue and the two disulphide bridges in bovine β-lactoglobulins A and B1, for each of which the monomer is a single chain of 162 residues and 18,000 molecular weight2,3, led to the conclusion that the sulphydryl group is at position 69, and that the disulphides bridge positions 123 to 160 and 57 to 70. These results were based on diagonal peptide studies4, and on the composition of peptides in which the sulphydryl group had been labelled with 14C-iodoacetamide, the disulphide bridges being left intact. Use was made of the partial amino-acid sequence given by Frank and Braunitzer5 and the reasonable assumption was made that the sulphydryl occurred in only one position. Subsequently, Shaw6 has shown that the sequence of Frank and Braunitzer5 showing Cys residues adjacent at positions 69 and 70 is incorrect, and that they are separated by a glutamine, the sequence for positions 67 to 71 for the Bvariant being Ala.Cys.Gln.Cys.Leu. Autoradiography of the dansyl amino-acid derivatives formed during the sequence determination of this pentapeptide indicated that both residues 68 and 70 seemed to have been labelled, and so we have given further consideration to the sulphydryl location. It has been found that although it does occur at 68, with 57 and 70 disulphide bridged, there is also an equal amount of protein present with the sulphydryl at 70, with 57 and 68 disulphide bridged. We discuss this additional finding here, and the significance for the determination of the location of sulphydryl groups in other proteins.
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McKENZIE, H., SHAW, D. Alternate Positions for the Sulphydryl Group in β-Lactoglobulin: the Significance for Sulphydryl Location in Other Proteins. Nature New Biology 238, 147–149 (1972). https://doi.org/10.1038/newbio238147a0
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DOI: https://doi.org/10.1038/newbio238147a0
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