IMMUNOLOGICAL DEMONSTRATION OF G(Q)-PROTEIN IN LIMULUS PHOTORECEPTORS

The phototransduction cascade in invertebrates involves the coupling o f rhodopsin activation to the action of the enzyme phospholipase C. Th is step is performed by G-proteins. An antibody against the cu-subunit of a mouse G(q) type G-protein recognized protein bands in Western bl ots of lateral eye and ventral nerve photoreceptors of Limulus. The pr otein bands had an apparent molecular mass of about 42 kDa. The antibo dy also recognized protein bands of a similar molecular mass in immuno blots of brain and intestine tissue. Immunoreactivity was found in lat eral eye frozen sections where it was confined to the rhabdom region. When the antibody was applied to ultrathin sections of ventral nerve p hotoreceptors, the highest density of labeling was found on the rhabdo meral microvilli, but gold particles were also scattered in the cytopl asm. We conclude that a G-protein of the type G(q) participates in the phototransduction of Limulus.