Abstract.-The complete amino acid sequence of a human yG1 immunoglobulin (Eu) has been determined and the arrangement of all of the disulfide bonds has been established. Comparison of the sequence with that of another myeloma protein (He) suggests that the variable regions of heavy and light chains are homologous and similar in length. The constant portion of the heavy chain contains three homology regions each of which is similar in size and homologous to the constant region of the light chain. Each variable region and each constant homology region contains one intrachain disulfide bond. The half-cystines participating in the interchain bonds are all clustered within a stretch of ten residues at the middle of the heavy chains.These data support the hypothesis that immunoglobulins evolved by gene duplication after early divergence of V genes, which specified antigen-binding functions, and C genes, which specified other functions of antibody molecules. Each polypeptide chain may therefore be specified by two genes, V and C, which are fused to form a single gene (translocation hypothesis). The internal homologies and symmetry of the molecule suggest that homology regions may have similar three-dimensional structures each consisting of a compact domain which contributes to at least one active site (domain hypothesis). Both hypotheses are in accord with the linear regional differentiation of function in antibody molecules.Antibodies or immunoglobulins can interact with a wide range of different antigenic determinants and, after specific binding to an antigen, they play a fundamental part in physiological functions of the immune response. The specificity of antigen binding depends ultimately upon amino acid sequences of the variable or V regions of antibody molecules. It is the diversity of these sequences which results in the range of specificities required for a selective immune response. In contrast, other regions of the antibody molecule have relatively constant sequences and are responsible for physiological functions. Like enzymes, these C regions appear to have evolved for a restricted set of interactions. This unusual picture of intramolecular differentiation has emerged from studies of the structure of immunoglobulins from different animal species.' To date, only portions of immunoglobulin molecules have been subjected to amino acid sequence determination.We now report the amino acid sequence of an entire human 'yG1 immunoglobulin (molecular weight 150,000), the location of all disulfide bonds, the arrangement of light and heavy chains, and the length of the heavy chain V region.78
The cell adhesion molecule (CAM) is involved in adhesion among embryonic retinal and brain cells and has been detected in a variety of neural tissues. This paper describes the use of spinal ganglion cultures and specific anti-CAM antibodies to determine the distribution of CAM on plasma membranes of nerve processes, and to assess the results of perturbation of its function during the growth of neurites from gapglia. The results indicate that CAM is distributed over the entire surface of nerve processes, and that specific anti-CAM Fab' fragments alter the morphology of neurite outgrowth. In particular, it was observed that anti-CAM inhibits formation of nerve bundles, so that the ganglion becomes surrounded by a tangled net of fine processes. Growth cone functions, such as neurite elongation, motility, and attachment to the substratum, did not appear to be affected by the antibody. These studies suggest that one of the major functions of CAM is to mediate side-to-side adhesion between neurites to form fascicles, and raise the possibility that this molecule serves a key role in embryogenesis of nerve tissues.
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