ウシ網膜桿体外節におけるGTP結合蛋白質(トランスデユーシン)の活性調節機序
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概要
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Transducin, a GTP-binding protein found in the bovine rod outer segment, mediates the signal coupling between rhodopsin and cGMP phosphodiesterase. Recent observations have revealed that transducin consists of two functional subunits: Tα (Mr 39,000) and Tβγ (Mr 35,000 and 8,000), and that photolyzed rhodopsin catalyzes the exchange of GTP for GDP bound to Tα and, in this case, Tβγ regulates the binding of GTP to Tα. This process, i. e., transducin activation, is an important amplified step to signal the start of transduction during photon absorption by rhodopsin. Therefore, we intended to elucidate the regulatory mechanism of the transducin activation in retina. We found subspecies of Tβγ during the purification of Tβγ from the bovine retinal rod outer segment. Purified Tβγ was separated into three components by chromatography on Mono-Q, an anion exchange column, equipped with FPLC. One of the components caused substantially no enhancement of GppNHp, a nonhydrolyzable analogue of GTP, binding activity to Tα in the presence of photolyzed rhodopsin. These findings indicate that there are functionally two different forms in Tβγ, i. e., active and inactive forms. Each Tβγ subspecies showed the same mobility as Tβ and Tγ in SDS-polyacrylamide gel electrophoresis (PAGE). The mobility of Tγ was distinctly different, however, between the active and inactive forms in 8M urea-PAGE and 8M urea-SDS-PAGE. Therefore, it is likely that the functional heterogeneity of Tβγ depends on the structural heterogeneity of Tγ. Purified Tγ was further separated into four subspecies (Tγ-1, Tγ-2, Tγ-3, and Tγ-4) by high-performance liquid chromatography on a C18 reverse phase column. ?However, the amino acid sequences of these four Tγ seemed to be identical to each other. These Tγ subspecies consisted of 68 amino acid residues, in which N-terminal amino acid was Pro and C-terminal amino acid was Gly. These results indicate that the structural heterogeneity of Tγ, which was shown by 8M urea electrophoresis, depends on its structural modification which introduces different surface charges on the molecule.
- 札幌医科大学の論文
- 1988-04-01
札幌医科大学 | 論文
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