Solubilized [formula omitted] from shark rectal gland and ox kidney — an inactivation study

Abstract

The bi-exponential time-course of detergent inactivation at 37°C of C 12E 8-solubilized (Na + + K +)-ATPase from shark rectal glands and ox kidney was investigated. The data for shark enzyme, obtained at detergent/protein weight ratios between 2 and 16, are interpreted in terms of a simple model where the membrane bound enzyme is solubilized predominantly as (alpha-beta) 2 diprotomers at low detergent concentrations and as alpha-beta protomers at high C 12E 8 (octaethyleneglycoldodecylmonoether) concentrations. It is observed that the protomers are inactivated 15-fold more rapidly than the diprotomers, and that the rate of inactivation of both oligomers is proportional to the detergent/protein ratio. Inactivation of kidney enzyme was biexponential with a very rapid inactivation of up to 40% of the enzyme activity. The observed rate of inactivation of the slower phase varied with the detergent/protein ratio, but the inactivation pattern for the kidney enzyme could not readily be accommodated within the model for inactivation of the shark enzyme. The rates of inactivation at 37°C were about the same in KCl and NaCl, i.e., in the E 2(K) and E 1 · Na forms, for both enzymes.