Characterization of reptilian vitellogenin: Subunit composition and molecular weights of vitellogenin from the colubrid snake Thamnophis sirtalis (L.)

1.1. Injecting the common garter snake, Thamnophis sirtalis, with 17β-estradiol caused an initial increase in the plasma concentration of protein-bound, alkaline-labile phosphorus. Females generally responded to a greater extent than did males.2.2. Concurrent with increased plasma phosphorus levels, hormone treatment induced the de novo synthesis of a single, high mol. wt protein (about 445,000), that we tentatively identified as vitellogenin.3.3. Electrophoresis of plasma samples from treated snakes, denatured with sodium dodecyl sulfate, revealed three bands not seen in samples from untreated animals: a darkly staining band (VgD, Mr ∼ 256,000) and two lightly staining bands (Vg1, Mr ∼ 149,000; Vg2, Mr ∼ 124,000).4.4. When denatured samples were reduced with dithiothreitol, VgD disappeared and the staining intensity of Vg2 increased markedly. The staining intensity of Vg1 did not change noticeably. Thus VgD appears to be a dimer of Vg2, joined covalently by disulfide bonds.5.5. We conclude that presumptive T. sirtalis vitellogenin, in its native state, does not display the dimeric structure so characteristic of other vertebrate Vgs. Molecular weight estimates of VgD, Vg1, and Vg2 suggest a trimeric structure for native Vg, but other polypeptide arrangements cannot be excluded.