Sarcoplasmic reticulum Ca(2+)-ATPase of sea cucumber smooth muscle: regulation by K(+) and ATP.
Although several Ca(2+)-ATPase isoforms have been described in vertebrates, little is known about Ca(2+)-transport in the muscle of invertebrates. In the microsomal fraction obtained from the sea cucumber (Ludwigothurea grisea) longitudinal body wall smooth muscle, we identified a Ca(2+)-transport ATPase that is able to transport Ca(2+) at the expense of ATP hydrolysis. This enzyme has a high affinity for both Ca(2+) and ATP, an optimum pH around 7.0, and - different from the vertebrate sarcoplasmic reticulum Ca(2+)-ATPases isoforms so far described - is activated 3- to 5-fold by K(+) but not by Li(+), at all temperatures, Ca(2+) and ATP concentrations tested. Calcium accumulation by the sea cucumber microsomes is inhibited by Mg/ATP concentrations >1 mM and the accumulated Ca(2+) is released to the medium when the ATP concentration is raised from 0.1 to 4.0 mM.
Landeira-Fernandez
A M
AM
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590, Rio de Janeiro, Brazil.
Galina
A
A
Jennings
P
P
Montero-Lomeli
M
M
de Meis
L
L
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002463:Cell Membrane Permeability; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology; D009130:Muscle, Smooth / Q000201:enzymology*; D019815:Oxalic Acid / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012616:Sea Cucumbers; D013379:Substrate Specificity; D013696:Temperature
D004791:Enzyme Inhibitors; D010710:Phosphates; D000255:Adenosine Triphosphate; D019815:Oxalic Acid; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D011188:Potassium; D002118:Calcium