Globulin subunit

The pattern of exons and introns (exon-intron-exon-intron-exon) in the a and /3 families of genes is quite old and apparently developed before the separation of these genes some 500 million years ago. The role of introns is unknown, although their base sequences vary. Because the introns are not transcribed, the protein sequences are unchanged. The introns appear to correspond to structural domains within the folded globulin subunits and are requisite for the posttranscriptional processing of mRNA. 

A later study (45) indicates that cucurbitin from pumpkin has a molecular weight of TT2,000 dal tons that can be electrophoretically separated into subunits of 63,000 and 56,000 dal tons. Reduction of disulfides produces polypeptides of 36,000 and 22,000 dal tons. Globulins from six cucurbits examined chromatographically (46) have molecular weights of 220,000 to 260,000 dal tons that exhibit predominantly 10.4 - 11.2 S values (about 95% of the three globulin fractions). Cucurbitin from Cucumis sativus appears a tetramer of... 

The iodothyronines are very insoluble molecules and are kept in solution by transport proteins. The most important of these is thyroxine binding globulin (TBG), which carries about 65% T and 70% Tj. It is a small (MW 60,000-65,000) glycoprotein consisting of four subunits. It has a single, high-affmity binding site for T, with an estimated of 1.2 x 10 °M. 

Mature 11S globulins are hexameric proteins that are initially assembled and transported through the secretory system as intermediate trimers. In the protein storage vacuole, the subunits of these trimers are proteolytically processed to yield... 

Thanh and Shibasaki (10) proposed a trimeric structure for the 7S and a hexamerlc structure for the 9S dimer. Urea/sodium dodecyl sulfate polyacrylamide gel electrophoresis resolves the 7S globulin into six isomeric forms which are made up of three types of subunits (a, a and B) in varying proportions (10, 14, 15). The composition of the six isomeric proteins has been designated as follows B.., B, aB2> B, aa B B,, a B ... 

Figure 13. Schematic structure of human yM-immunoglobulin molecule. The heavy lines between each yG-immuno-globulin like subunit, as well as within each subunit, represent disulfide bonds.

Fig. 6. Schematic representation of the hydrolysis of native rabbit y-globulin or specific rabbit antibodies by proteolytic enzymes. y-Globulin contains four polypeptide chains. Two chains have a molecular w eight of 50,000 (A) and two others (B) a molecular weight of 25,000. Proteolysis and cleavage of one disulfide bond results in preferential cleavage of the tw o A-chains with the production of two types of subunits. After Fleischman et al. (1963).

Factor IX 57,000 ai Globulin Single polypep- 2 Subunits Serine protease... 

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