Letter | Published:

Comparison of the C-terminal Amino-acid Sequence of Two Horse Immunoglobulins IgG and IgG(T)

Naturevolume 212pages205206 (1966) | Download Citation



IT was observed that treatment of the heavy chain of normal rabbit immunoglobulin G (IgG) with cyanogen bromide in 70 per cent formic acid split the chain into sections suitable for amino-acid sequence studies. Cyanogen bromide reacts with methionine residues converting them to homoserine with simultaneous splitting of the peptide chain and leaving the homoserine residue C-terminal1. Particularly the C-terminal octadecapeptide was easily isolated in high yield and its sequence was determined2. The heavy chain of human IgG from normal serum3 and a pathological serum4 both had the same C-terminal sequence and this differed from that of the rabbit in only two of the eighteen residues, suggesting that there might be a characteristic pattern for all mammalian IgG. The heavy chain of horse IgG has been investigated by the same technique and compared with the heavy chain of the horse T protein. The latter immunoglobulin is barely detectable in normal serum but increases very considerably in the serum of a horse strongly immunized with protein antigens such as diphtheria or tetanus toxoid and it may contain almost all the antibody5,6. This protein has a high carbohydrate content and it has been suggested that it might be the equine equivalent of human IgA. From a study of the antigenic cross-reactions of the whole proteins and their subunits, however, this seemed unlikely7.

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  1. R. C. WEIR: Department of Chemical Pathology, Guy's Hospital Medical School London, S.E.1.

  2. D. GIVOL: The Weizmann Institute, Rehovoth, Israel.


  1. Department of Immunology, St. Mary's Hospital Medical School, London, W.2

    • R. C. WEIR
    • , R. R. PORTER
    •  & D. GIVOL


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