1. 1. The transfer of sodium and fluid across everted sacs of goldfish intestine fell to half the control values 18-24 hr after raising the environmental temperature from 16 to 30°C. The Na+/K+-ATPase activity fell in membranes prepared from 16°C adapted fish kept at 30°C but this took 20 days to become apparent. 2. 2. The amount of tritiated ouabain bound to membranes prepared from the intestines of 16°C adapted fish was the same as that bound to membranes prepared from 16°C adapted fish kept at 30°C for 20 days. The time course of ouabain binding was also the same, both in the presence and absence of ATP. The ATP-dependent binding was 4 times the non-specific binding. 3. 3. The turnover number for the Na+/K+-ATPase system (ATPase activity/ amount of ATP-dependent bound ouabain) fell by one third when 16°C adapted fish were kept at 30°C for 20 days. The turnover numbers for Na+/K+-ATPase from fish kept at 30°C for shorter periods of time were not significantly differrent those obtained from the 16°C adapted fish. 4. 4. The discrepancy between the time taken for sodium transport and Na+/ K+-ATPase activity to adapt suggests that the two are not directly related. © 1971.
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