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.
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590, Rio de Janeiro, Brazil.
A M
AM
Landeira-Fernandez
A
A
Galina
P
P
Jennings
M
M
Montero-Lomeli
L
L
de Meis
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