FORMATION OF VESICLES BY THE ACTION OF ACYL-COA-1-ACYLLYSOPHOSPHATIDYLCHOLINE ACYLTRANSFERASE FROM RAT-LIVER MICROSOMES - OPTIMAL SOLUBILIZATION CONDITIONS AND ANALYSIS OF LIPID-COMPOSITION AND ENZYME-ACTIVITY
H. Fyrst et al., FORMATION OF VESICLES BY THE ACTION OF ACYL-COA-1-ACYLLYSOPHOSPHATIDYLCHOLINE ACYLTRANSFERASE FROM RAT-LIVER MICROSOMES - OPTIMAL SOLUBILIZATION CONDITIONS AND ANALYSIS OF LIPID-COMPOSITION AND ENZYME-ACTIVITY, Biochemistry, 35(8), 1996, pp. 2644-2650
The enzyme acyl coenzyme A:1-acyllysophosphatidylcholine acyltransfera
se (acyl-CoA:lysoPC acyltransferase) can be isolated in newly formed p
hosphatidylcholine (PC) vesicles by solubilization of rat liver micros
omes with the two substrates lysoPC and acyl-CoA. In this study, we so
ught to optimize the conditions for the formation of PC vesicles and a
nalyzed the lipid composition and enzyme activity of the newly formed
vesicles. Analysis of PC vesicles formed by incubation of the microsom
al preparation with 1-(C-16:0)lysoPC and C(18:1)CoA, C(18:2)CoA, or C(
20.4)CoA showed that the optimal protein:lysoPC ratio was 1:5 (by weig
ht) and the optimal lysoPC:acyl-CoA ratio was 1:1 (molar amounts). PC
formation increased with incubation time; after 20 h of incubation at
37 degrees C, approximately 75% of the lysoPC was converted to PC in t
he incubation mixture. The phospholipid molecular species composition
of the vesicles reflected almost exclusively the substrates used; the
vesicles contained approximately 33% of the total acyl-CoA:lysoPC acyl
transferase activity from the microsomes and demonstrated a single pro
tein band with a molecular mass of 21 kDa by gel electrophoresis. The
procedure selected for the enzyme specific for lysoPC acylation, as en
zyme activity toward lysophosphatidylethanolamine (lysoPE), lysophosph
atidylserine (lysoPS), and lysophosphatidylinositol (lysoPI), was very
low. In addition, the utilization of different acyl-CoA substrates fo
r acylation of lysoPC was different from that in microsomes, These res
ults show that an enzyme specific for the formation of PC from lysoPC
can be isolated in PC vesicles with a designed phospholipid molecular
species composition and that the lipid environment plays sin important
role in the regulation of the enzyme's affinity for its substrates.