The mechanism of transducin light dependent activation by rhodopsin gdp gtp exchange or phosphorylation of transducin bound gdp?
Dizhur, A.M.; Arshavskii, V.Yu; Kaulen, A.D.; Filippov, P.P.
Biologicheskie Membrany 3(7): 691-696
1986
ISSN/ISBN: 0233-4755 Accession: 006716307
According to the wide-spread viewpoint, photo-excited rhodopsin-catalyzed activation of transducin in the rod outer segments is caused by the exchange of transducin-bound GDP for GTP. The alternative hypothesis postulates that transducin activation is based not on the GDP/GTP exchange, but on rapid light-dependent phosphorylation of transducin-bound GDP at the expense of exogenous ATP. In the present work the light scattering signals, reflecting the transducin activation state in the transducin-photoreceptor membrane system, were measured and the phosphorylation efficiency of transducin-bound GDP in the presence of GDP + ATP and GDP + GTP in response to illumination was determined. The experimental data thus obtained provide evidence in favour of the transducin activation mechanism involving fast GDP/GTP exchange, rather than light-dependent phosphorylation of transducin-bound GDP.