TRANSDUCIN ACTIVATION BY MOLECULAR SPECIES OF RHODOPSIN OTHER THAN METARHODOPSIN II*

Abstract

[1] Decay of metarhodopsin II was accelerated by hydroxylamine treatment or dark incubation of metarhodopsin II at 30°C. The products thus obtained after decay of metarhodopsin II induced GTPase activity on transducin as well as metarhodopsin II suggesting that rhodopsin could activate transducin after the decay of metarhodopsin II intermediate. [2] After urea‐treated bovine rod outer segment membrane was completely bleached, rhodopsin in the membrane was regenerated by the addition of 11‐cis retinal at various temperatures between 0 and 37°C. The capacity to induce GTPase activity on transducin and phosphate incorporating capacity catalyzed by rhodopsin kinase were measured on such rhodopsins. The results showed that: (1) Regeneration of alpha band of rhodopsin was complete regardless of regeneration temperature; (2) When regenerated at temperatures below 10°C, rhodopsins induced a GTPase activity on transducin in the dark even after treatment with hydroxylamine, whereas rhodopsins after regeneration at temperatures above 13°C did not; (3) When regenerated at 0°C, rhodopsin was phosphorylated if incubated with rhodopsin kinase and ATP in the dark, whereas the spectrally regenerated rhodopsin at 30°C was not. The complete quenching of functions of photoactivated rhodopsin was achieved by recombination with 11‐cis retinal at temperatures above 13°C but not below 10°C suggesting the existence of a low temperature intermediate upon regeneration. Nishigonaka, Okazaki 444. Japan.