ADIPOSE MONOACYLGLYCEROL-ACYL-COENZYME-A ACYLTRANSFERASE ACTIVITY IN THE WHITE-THROATED SPARROW (ZONOTRICHIA-ALBICOLLIS) - CHARACTERIZATIONAND FUNCTION IN A MIGRATORY BIRD
N. Mostafa et al., ADIPOSE MONOACYLGLYCEROL-ACYL-COENZYME-A ACYLTRANSFERASE ACTIVITY IN THE WHITE-THROATED SPARROW (ZONOTRICHIA-ALBICOLLIS) - CHARACTERIZATIONAND FUNCTION IN A MIGRATORY BIRD, Lipids, 29(11), 1994, pp. 785-791
Although migrating birds use stored triacylglycerol as their primary f
uel for flight, they must retain sufficient stores of omega 6 and omeg
a 3 fatty acids to sustain reproduction after the spring migration. He
patic monoacylglycerol:acyl-coenzyme A acyltransferase (EC 2.3.1.22) (
MGAT) activity is associated with physiological peri ods in which lipo
lysis and beta-oxidation are prominent, and it may also play a role in
the selective retention of certain essential fatty acids. Therefore,
we characterized MGAT activity in adipose tissue from the white-throat
ed sparrow (Zonotrichia albicollis), a migratory bird. MGAT specific a
ctivity from adipose tissue and liver, respectively, was 22.2 +/- 7.27
and 0.79 +/- 0.35 nmol/min/mg of total particulate protein. Activity
did not vary seasonally or between male and female birds. Specific act
ivity increased 4.3 fold in the presence of 75 mu g of phosphatidylcho
line and phosphatidylserine (1:1, w/w). MGAT acylated sn-1(3)-monooleo
ylglycerol, sn-2-monooleylglycerol ether and sn-1(3)-monooleylglycerol
ether at 7.5, 5.7 and 1.7%, respectively, of the rate observed with s
n-2-monooleoylglycerol. An initial lag phase observed at low concentra
tions of palmitoyl-CoA was corrected by adding 2 mM MgCl2, Mg(NO3)(2)
or CaCl2, suggesting a requirement for divalent cations. MGAT acylated
sn-2-monolinolenoylglycerol and sn-2-monolinoleoylglycerol in prefere
nce to sn-a-monooleoylglycerol. Specificity of MGAT for sn-2-monoacylg
lycerols and the probable enhanced affinity for sn-2-monoacylglycerols
of specific acyl chains may allow selected omega 6 and omega 3 fatty
acids to be retained within the adipocyte, while nonessential fatty ac
ids are released for beta-oxidation in flight muscles.