Ml. Blank et al., THE COA-INDEPENDENT TRANSACYLASE IN PAF BIOSYNTHESIS - TISSUE DISTRIBUTION AND MOLECULAR-SPECIES SELECTIVITY, Biochimica et biophysica acta, L. Lipids and lipid metabolism, 1254(3), 1995, pp. 295-301
Microsomal membranes from six different rat tissues (spleen, lung, kid
ney, brain, testis, and liver) were found to possess CoA-independent t
ransacylase activity that could both acylate lyso-[H-3]PAF [H-3]hexade
cyl-2-lyso-sn-glycero-3-phosphocholine) and then deacylate the -[H-3]h
exadecyl-2-acyl-sn-glycero-3-phosphocholine product via the transacyla
tion of added exogenous k-1'-enyl-2-lyso-sn-glycero-3-phosphoethanolam
ine. Platelet-activating factor -3]hexadecyl-2-acetyl-sn-glycero-3-pho
sphocholine) was produced when acetyl-CoA was added to the spleen micr
osomes during generation of lyso-[H-3]PAF by the transacylases. More e
xtensive studies with subcellular fractions from spleen revealed that,
in addition to microsomes, the transacylase activities were also pres
ent in the 15 000 X g membrane fraction but not in the cytosol. Analys
is of molecular species of 1-[H-3]hexadecyl-2-acyl-sn-glycero-3-phosoc
holine before and after addition of lk-1'-enyl-2-lyso-sn-glycero-3-pho
sphoethanolamine as the acyl acceptor demonstrated a high selectivity
for polyunsaturated fatty acids (> 3 double bonds/acyl group) in both
the acylation and deacylation processes that occurred in testicular mi
crosomal membranes. The transfer of acyl groups by the transacylase ap
peared to be equally effective for either arachidonic or docosapentaen
oic(n - 6) fatty acids, whereas linoleic and oleic fatty acids were no
t transferred from -[H-3]hexadecyl-2-acyl-sn-glycero-3-phosphocholine
following the addition of lk-1'-eny-2-lyso-sn-glycero-3-phosphoethanol
amine. Similar experiments with the membrane fraction of undifferentia
ted HL-60 cells showed that arachidonic acid supplementation of intact
cells enhanced both the CoA-independent transacylation of lyso-[H-3]P
AF and the subsequent deacylation of [H-3]hexadecyl-2-acyl-sn-glycero-
3-phosjphocholine caused by addition of -1'-enyl-2-acyl-sn-glycero-3--
phosphoethanolamine. Differentiation of the HL-60 cells into a neutrop
hil-like form had no effect on the transacylase activity. Our results
indicate the PAF-related transacylase is widely distributed among tiss
ues and, although highly selective for polyunsaturated acyl groups, do
es not discriminate selectively among the polyunsaturates.