[Calmodulin-induced activation of ATP-dependent Ca2+ transport in plasma membranes of the myometrium].
Calmodulin activates the ATP-dependent transport of Ca2+. The V0 value for this reaction in the absence of calmodulin is 0.82, that in the presence of 10(-7) M calmodulin is 5 times as high, i. e. 4.5 nmol 45Ca2+/mg protein/min. The Vmax value in the absence of calmodulin is 2.07, that with the activator is 4.33 nmol 45Ca2+/mg protein/min. The corresponding Km values are 0.75 X 10(-6) M and 0.66 X 10(-7) M, respectively, i. e., the affinity of the Ca-pump for Ca2+ increases. The half-maximum Ca-binding activity of calmodulin measured with a help of the fluorescent probe, N-phenyl-1-naphthylamine (PNA), is observed at 5 X 10(-7) M Ca2+. Mg2+ (3 mM) decreases 10-fold the Ca-binding affinity. No significant effect of ATP on the Ca-binding properties of calmodulin was found; the Hill coefficient is suggestive of a positive cooperativity of this reaction. A comparison of dependences of the calmodulin-stimulated component of ATP-dependent transport of Ca2+ in myometrium plasma membranes and of the Ca-binding activity of calmodulin measured with a help of PNA suggests that the effect of calmodulin on the affinity of the Ca-pump for Ca2+ can also be realized when some (but not all) Ca-binding sites in the calmodulin molecule are saturated with Ca2+.
Prishchepa
L A
LA
Kondratiuk
T P
TP
Kurskiĭ
M D
MD
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D009215:Myometrium / Q000378:metabolism*; D013552:Swine
D002147:Calmodulin; D000255:Adenosine Triphosphate; D002118:Calcium
Aktivatsiia kal'modulinom ATP-zavisimogo transporta Ca2+ v plazmaticheskikh membranakh miometriia.