The plasma-membrane H(+)-ATPase from beet root is inhibited by a calcium-dependent phosphorylation.
Several plasma-membrane proteins from beet root (Beta vulgaris L.) have been functionally incorporated into reconstituted proteoliposomes. These showed H(+)-ATPase activity, measured both as ATP hydrolysis and H+ transport. The proton-transport specific activity was 10 times higher than in plasma membranes, and was greatly stimulated by potassium and valinomycin. These proteoliposomes also showed calcium-regulated protein kinase activity. This kinase activity is probably due to a calmodulin-like domain protein kinase (CDPK), since two protein bands were recognized by antibodies against soybean and Arabidopsis CDPK. This kinase phosphorylated histone and syntide-2 in a Ca(2+)-dependent manner. Among the plasma-membrane proteins phosphorylated by this kinase, was the H(+)-ATPase. When the H(+)-ATPase was either prephosphorylated or assayed in the presence of Ca2+, both the ATP-hydrolysis and the proton-transport activities were slower. This inhibition was reversed by an alkaline-phosphatase treatment. A trypsin treatment (that has been reported to remove the C-terminal autoinhibitory domain from the H(+)-ATPase) also reversed the inhibition caused by phosphorylation. These results indicate that a Ca(2+)-dependent phosphorylation, probably caused by a CDPK, inhibits the H(+)-ATPase activities. The substrate of this regulatory phosphorylation could be the H(+)-ATPase itself, or a different protein influencing the ATPase activities.
Lino
B
B
Departamento de Biotecnología y Bioquímica, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del IPN, Gto, México.
Baizabal-Aguirre
V M
VM
González de la Vara
L E
LE
D002118:Calcium / Q000378:metabolism*; D019663:Chenopodiaceae / Q000201:enzymology*; D006868:Hydrolysis; D017136:Ion Transport; D010766:Phosphorylation; D018517:Plant Roots / Q000201:enzymology*; D011494:Protein Kinases / Q000378:metabolism; D011510:Proteolipids; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology
D011510:Proteolipids; C020485:proteoliposomes; D011494:Protein Kinases; D014357:Trypsin; D006180:Proton-Translocating ATPases; D002118:Calcium