Is Ca2+ effect on passive K+ transport mediated by spectrin--dependent ATPase?
Abstract:
The aim of this report was to find which part of the membrane is responsible for the Ca2+ dependence of membrane permeability to K+. We found that the enzyme activity of large contractile complex of membrane proteins, the so called spectrin-dependent ATPase (sp-ATPase) increases at certain Ca2+ concentrations when K+ permeability decreases and vice versa. Ca2+ apparent dissociation constant for sp-ATPase is 6 X 10(-7) M which is the value corresponding to findings of Porzig and Stoffel (1978) for Ca2+ binding to membrane with low K+ permeability. Moreover, 20 chemically quite different substances which inhibit sp-ATPase activity simultaneously increase in the same concentrations K+ permeability and vice versa. No exception was found. The results show that low membrane permeability to K+ occurs at such conformation of sp-ATPase at which its enzyme activity may fully be manifested whereas at other conformations permeability to K+ increases. The conformation of sp-ATPase seems to affect gating mechanism of a respective channel for passive K+ transport through membrane.
Related Concept Videos
Primary Active Transport
Secondary Active Transport
Primary Active Transport
Secondary Active Transport
ATP Driven Pumps II: P-type Pumps
A typical P-type pump has three cytosolic domains: nucleotide-binding (N), phosphorylation (P), and activator (A) domains. These domains are connected to the membrane-spanning helices by short amino acid segments. ATP hydrolysis and covalent phosphoenzyme intermediate formation are crucial parts of the catalytic cycle. At the highly...
Active Transport
Primary active transporters, like Na+, K+ and -ATPase, directly utilize ATP to move ions across the membrane. These transporters play significant roles in various physiological processes. For instance, Na+, K+ and -ATPase maintain...


