N- and C-terminal sequences in pig immunoglobulin pi-chains: Assignment to the K type

Amino acid sequence of the constant region of immunoglobulin light chains from Rana catesbeiana

Little is known about the detailed structure of immunoglobulins in non-mammalian vertebrates. We have determined the amino acid sequence of the constant region of immunoglobulin light chains from the bullfrog, Rana catesbeiana. There appears to be one major type of light chain in this species. However, at position 153, about half of the chains have lysine, the remainder having arginine. Variation at this same or at an adjacent position is responsible for allotypic or isotypic variation in human kappa and lambda chains. At three positions (118, 119, and 181), residues that occur in all known kappa and lambda chains in other species are replaced in the Rana catesbeiana sequence. One of these unusual substitutions--the replacement of proline by cysteine at position 119--allows the formation of an extra intrachain disulfide bond within the constant domain, between positions 119 and 214. This bond appears to replace the usual disulfide bridge between heavy and light chains so that, in the immunoglobulins of this species, the light chains are not covalently bonded to heavy chains. The sequence of the Rana catesbeiana constant region is compared to sequences of a variety of mammalian light chain constant regions. We consider the implications of these comparisons for the timing of the divergence of kappa and lambda chains relative to the divergence of the lineages leading to amphibians and to mammals and birds.

The subclass heterogeneity of pig IgG

The recognition and distinction of pig IgG subclasses is a difficult task because no pathological monoclonal immunoglobulins of pig origin are available. Attempts at elucidating the subclass composition of pig IgG based on subfractionation of pooled IgG and preparation of antisera has led to only partial success. Chemical evidence for heterogeneity of the constant portion of pig gamma-chains pointed to the existence of more than one subclass; a final answer to the question of the number of subclasses could not be obtained. Functionally different antibodies of the IgG class may be isolated from immune sera collected at various stages of the immune response. Precipitating and nonprecipitating anti-dinitro-phenyl (DNP) antibodies differ chiefly in their capacity for forming insoluble complexes with DNP-carrier proteins. Examination of these antibodies by physical methods showed that the precipitating antibody is less compact, more flexible and that the distance between the two binding sites on the same molecule are greater than for the nonprecipitating anti-DNP antibody. The precipitating antibody is very resistant to cleavage by pepsin compared to the non-precipitating antibody. This resistance, together with the differences in the molecular parameters described above provides evidence that precipitating and nonprecipitating anti-DNP antibodies in swine are representatives of separate IgG subclasses. Mouse monoclonal antibodies to pig IgG show a degree of selectivity for certain IgG subpopulations when tested against pooled pig IgG. The limited number of monoclonal antibodies currently available does not allow final conclusions to be drawn on the number of pig IgG subclasses.