Chain Isotypic Determinants

The X light chains have been shown to express a number of antigenic determinants which also reflect isotypic differences (Fett and Deutsch, 1975). Two distinct antigenic types of human X chains, termed Oz and Oz , were originally thought to be allotypic markers (see below) but were later shown by genetic analyses to be isotypic in nature. Both types of chain are thus found in all normal individuals. The structural correlate 

Still another X chain variant has been described by Fett and Deutsch (1975) totally on the basis of the primary structure of a X chain termed Meg and related proteins. This variant is correlated with differences in three positions of the Meg X constant region, as compared with other X proteins. Meg variants have asparagine at position 116, threonine at position 118, and lysine at position 167. Mcg proteins, on the other hand, have alanine, serine, and threonine at these respective positions (Table I). 

Very recently, Solomon (1977) has shown that the distinct antigenic determinants characteristic of the two variants can both be detected serologically by appropriate antisera. The determinants involved in the Meg isotype are complex since their expression is dependent on the presence of both the variable and constant domains of the X chain, in spite of the fact that the primary structure correlates are entirely in the constant region, as established by the studies of Fett and Deutsch (1975). Very likely, as proposed by Solomon, the amino-terminal segment of the variable domain participates in the expression of the determinant associated with the Meg variants. 

Noiiisotypic Light-Chain Constant Region Determinants 

An undoubtedly related phenomenon has been seen with respect to the influence of interchain disulfide bonds on the detection of light-chain-specific and other types of immunoglobulin determinants. It is occasionally observed that the simple reduction of an immunoglobulin, by the inclusion of a mercaptan reductant in the buffer, will facilitate the detec- 

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It seems clear that the existence of distinct isotypic determinants is due to specific conformational features of the constant region of the heavy chains of immunoglobulins. Unlike for some other protein systems, however, such as myoglobin (Atassi, 1975) and lysozyme (Atassi et al., 1976 Lee and Atassi, 1977a,b Atassi and Lee, 1978a,fo Atassi, 1978), the location of the various determinants has not been precisely mapped and correlated with particular structural features. 

The gene encoding Hp is on chromosome 16 at band q22. Both chains are polymorphic, but the a-chain accounts for the commonly recognized isotypes. As mentioned previously, the a-chains exist in different genetically determined sizes, with the basic monomer. The two common a variants, and differ only in one amino acid at position 54 (lysine in a " and glutamic acid in a ). Of the two, is the more frequent. 

The structure of CaCl2,Ca(B03)2 consists of Ca, Cr, and BO in distinct, mutually alternating anionic and cationic layers parallel to (102). The BO3 units are very nearly planar, and the B—O distances are 1.403,1.391, and 1.390 A. RbNbB Oft is isotypic with TlNbB206, but tilting of the octahedral chains in the a direction reduces the symmetry from Pnlxm to The crystal structure of synthetic anhydrous chondrodite, Al4<2o(B04)202, has been determined. The cation distribution among the three independent octahedral... 

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