. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 60000 50 100 150 Time (min) 200. 50 100 Time (min) 150 200 Figure 2. Time course of [3!S]GTP[S] binding determined at atmo- spheric pressure (5°C). in the absence (open symbols) and presence (filled symbols) of 10 fi/W R-PIA. Upper panel: Sebastulobus alascanus. Lower panel: S. altivelis. Each point is the mean of three determinations. The standard errors are smaller than the symbols. colonizing the deep ocean because of the large number of G protein-coupled transmembrane signaling systems (Siebe- naller and Murray. 1995). A
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 60000 50 100 150 Time (min) 200. 50 100 Time (min) 150 200 Figure 2. Time course of [3!S]GTP[S] binding determined at atmo- spheric pressure (5°C). in the absence (open symbols) and presence (filled symbols) of 10 fi/W R-PIA. Upper panel: Sebastulobus alascanus. Lower panel: S. altivelis. Each point is the mean of three determinations. The standard errors are smaller than the symbols. colonizing the deep ocean because of the large number of G protein-coupled transmembrane signaling systems (Siebe- naller and Murray. 1995). Among the loci of pressure per- turbation in these pathways, the intrinsic GTPase activities of the G protein a subunits are affected by increased pres- sure (Siebenaller and Murray. 1994a). In brain membranes of the congeneric Sebastolobus species, increased pressure (340 atm) decreased the apparent Km of GTP about 10% and increased Vmax values. Thus, increased pressure stimulates the high-affinity GTPase activity of G protein a subunits and may perturb transmembrane signal transduction by pre- maturely terminating signaling. The exchange of GTP for GDP is thought to be the rate-limiting step of the GTPase reaction (Higashijima et til., 1987). The present study ex- amined this exchange reaction. Increased pressure can alter this exchange and differentially affects the process in brain membranes of the Sebastolobus species. At atmospheric pressure, the GTP-GDP exchange occurs at different rates in the two species. The tu2 values, which are determined by the on (k,)n) and off (kotf) rates of GTP[S] and the concentration of [ S]GTP[S] used, differ between the two species. The exchange occurs faster in S. alascanus brain membranes (Fig. 2, Table I). The on rate in S. alas- ctunis is X 107 M~[ min~', in contrast to the kon value of X 107 M~l min ] in brain membranes of S. altivelis. These different rates of GTP binding may reflect differences in the coupling of G protei
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
