title: Role of the phospholipid environment in modulating the activity of the rat brain synaptic plasma membrane Ca2(+)-ATPase.
abstract: The role of the phospholipid environment in modulating the activity of the rat brain synaptic plasma membrane (SPM) Ca2(+)-ATPase was investigated by its reconstitution into different phospholipids. Retention of activity of the solubilized Ca2(+)-ATPase depended on addition of exogenous phospholipids. As the cholate concentration used for solubilization of native SPM increased, a larger excess of exogeneous phospholipids, relative to membrane protein, had to be added to maintain optimal activity. Highest ATP-dependent Ca2+ transport activity was obtained when reconstitution was carried out in calf brain phospholipids (BPLs) followed by soybean phospholipids (SPLs) and the lowest in egg PC; reconstitution at a 40:1 weight ratio of exogenous phospholipids to native SPM protein resulted in ATP-dependent Ca2+ transport of 40.0 +/- 4.16, 23.4 +/- 8.48, and 11.54 +/- 2.31 nmol of Ca2+ (mg of protein)-1 (5 min)-1, respectively. Partial substitution of egg PC with BPLs led to an increase in the activity of the reconstituted Ca2+ pump. The highest ATP-dependent Ca2+ uptake was obtained when ratios of 15:25 or 10:30 egg PC to BPLs were used. Testing the individual phospholipids participating in the BPL mixture showed that addition of PS to egg PC led to a consistent increase in Ca2+ pump activity. Substitution of 50% of the PC with PS resulted in a 3.8-fold higher ATP-dependent Ca2+ uptake than that obtained in egg PC alone. No other phospholipid tested--PE, SM, or PI--had a similar effect. Increasing the proportion of PS within the BPL mixture above its original content led to a gradual decrease in the reconstituted SPM Ca2+ pump activity. Enrichment of asolectin with PS led first to increased Ca2+ pump activity; then, as the proportion of PS increased, Ca2+ transport of the reconstituted pump decreased. An increased proportion of PE, SM, or PI within the BPLs or asolectin, above their original contents, resulted in decreased Ca2+ transport. These results indicate that optimal SPM Ca2+ pump activity requires the combined presence of a critical amount of PC and PS within the reconstituted membrane.
authors.affiliation: Department of Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel.
authors.forename: M
authors.initials: M
authors.lastname: Hermoni-Levine
authors.forename: H
authors.initials: H
authors.lastname: Rahamimoff
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D019826:Cholic Acid; D002793:Cholic Acids; D066298:In Vitro Techniques; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D012995:Solubility; D013569:Synapses / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D002793:Cholic Acids; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids; D000252:Calcium-Transporting ATPases; D019826:Cholic Acid