Temperature effects on sodium pump phosphoenzyme distribution in human red blood cells

20Citations
Citations of this article
14Readers
Mendeley users who have this article in their library.
Get full text

Abstract

Phosphorylation of red cell membranes at ambient temperatures with micromolar [32P]ATP in the presence of Na ions produced phosphoenzyme that was dephosphorylated rapidly upon the addition of ADP or K ions. However, as first observed by Blostein (1968, J. Biol. Chetn., 243:1957), the phosphoenzyme formed at 0°C under otherwise identical conditions was insensitive to the addition of K ions but was dephosphorylated rapidly by ADP. This suggested thatjthe conformational transition from ADP-sensitive, K-insensitive Na pump phosphoenzyme (E1-P) to K-sensitive, ADP-insensitive phosphoenzyme (E2P) is blocked at 0°C. Since the ATP: ADP exchange reaction is a partial reaction of the overall enzyme cycle dependent upon the steady state level of E1-P that is regulated by [Na], we examined the effects of temperature on the curve relating [Na] to ouabain-sensitive ATP:ADP exchange. The characteristic triphasic curve seen at higher temperatures when [Na] was between 0.5 and 100 mM was not obtained at 0°C. Simple saturation was observed instead with a K0.5 for Na of - 1 mM. The effect of increasing temperature on the ATP: ADP exchange at fixed (150 mM) Na was compared with the effect of increasing temperature on (Na + K)-ATPase activity of the same membrane preparation. It was observed that (a) at 0°C, there was significant ouabain-sensitive ATP:ADP exchange activity, (b) at 0°C, ouabain-sensitive (Na + K)-ATPase activity was virtually absent, and (c) in the temperature range 5-37 °C, there was an ~300-fold increase in (Na + K)-ATPase activity with only a 9-fold increase in the ATP:ADP exchange. These observations are in keeping with the suggestion that the Ei-P → E2P transition of the Na pump in human red cell membranes is blocked at 0°C. Previous work has shown that the inhibitory effect of Na ions and the low-affinity stimulation by Na of the rate of ATP: ADP exchange occur at the extracellular surface of the Na pump. The absence of both of these effects at 0°C, where Ei-P is maximal, supports the idea that external Na acts through sites on the E2P form of the phosphoenzyme. © 1985, Rockefeller University Press., All rights reserved.

Cite

CITATION STYLE

APA

Kaplan, J. H., & Kenney, L. J. (1985). Temperature effects on sodium pump phosphoenzyme distribution in human red blood cells. Journal of General Physiology, 85(1), 123–136. https://doi.org/10.1085/jgp.85.1.123

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Save time finding and organizing research with Mendeley

Sign up for free