Pressure induced intermediates in the photochemical reaction of squid rhodopsin.
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In squid giant axons, a brief rise and fall in intracellular pressure that was concomitant with the action potential was detected by using a glass-fiber device. The amplitude of the pressure change was about 1 mPa.
While it has been reported that general anaesthetics inhibit the enzyme luciferase and thus reduce the light output of the reaction with luciferin, we find that in squid giant axons injected with luciferin and luciferase, treatment with experimental general anaesthetics at concentrations sufficient to block axonal conduction leads to an increase in the light production by the reaction. This potentiation of the protein activity is best observed when luciferin concentration is above the apparent association constant. Our findings raise doubts regarding the suitability of luciferase as a model for the target region of general anesthetic action.
On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. 186, 1), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with that of Noda et al. (Nature 320; 188-192, 1986).
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When a nerve gas hydrolyzing enzyme [organophosphorus acid anhydrolase (OPAA), formerly DFPase] purified from squid hepatopancreas was injected into rabbits, the resulting sera (RAS) inhibited OPAA purified from either squid hepatopancreas or squid optic ganglia. The inhibition was non-competitive, with 50% inhibition at a 1:1,000 serum dilution, and with the limit of inhibition (in effect, a "titer") at approximately 1:10,000. This RAS did not inhibit the distinctly different OPAAs from a mammalian and two bacterial sources. The hepatopancreas-generated RAS also reacted positively to the appropriate enzyme-linked immunosorbent assay (ELISA) at a titer of 1:100,000. In marked contrast, when OPAA purified from squid optic ganglion was injected into rabbits, the resulting sera did not inhibit squid OPAA, and did not give a positive ELISA. Control sera taken from the same rabbits prior to any injection (RS) did not inhibit the OPAAs. These results show another major difference between squid type OPAAs and the OPAAs from other sources, sometimes termed "Mazur type" OPAAs.
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