STUDIES ON THE SUBCELLULAR-DISTRIBUTION OF 1-O-ALKYL-2-ACETYL-SN-GLYCERO PHOSPHOCHOLINE (PAF) AND ON THE ENZYMATIC-ACTIVITIES INVOLVED IN ITS BIOSYNTHESIS WITHIN THE CILIATE TETRAHYMENA-PYRIFORMIS
Dc. Tsoukatos et al., STUDIES ON THE SUBCELLULAR-DISTRIBUTION OF 1-O-ALKYL-2-ACETYL-SN-GLYCERO PHOSPHOCHOLINE (PAF) AND ON THE ENZYMATIC-ACTIVITIES INVOLVED IN ITS BIOSYNTHESIS WITHIN THE CILIATE TETRAHYMENA-PYRIFORMIS, Biochimica et biophysica acta, 1170(3), 1993, pp. 258-264
The ciliated protozoan Tetrahymena pyriformis contains platelet-activa
ting factor (PAF) as a physiological minor lipid. Its subcellular loca
lization was found as follows: 13.7% in the pellicles, 24.9% in mitoch
ondria, 56.5% in microsomes and 7.1% in the cytosol. Succinate dehydro
genase was used as marker enzyme. PAF remains cell-associated unless b
ovine serum albumin is included in the extracellular medium, In this c
ase 15% of total PAF, portion comparable to that found in the pellicle
s, is released. Investigation of the principal enzymic activities invo
lved in PAF formation showed that PAF-acetyltransferase (2.3.1.67) is
totally absent from the protozoan. This means that the 'remodelling' p
athway occurring in pro-inflammatory cells does not contribute in PAF
formation in our system. A dithiothreitol (DTT)-insensitive CDPcholine
phosphocholinetransferase activity involved in PAF biosynthesis is sh
own for the first time to be responsible for PAF production in T pyrif
ormis. It uses exogenous alkyl-acetyl-glycerol as substrate and is sat
urated over substrate concentration 250 muM. It can also use endogenou
s lipids as substrate. It is distributed mainly in mitochondria and mi
crosomes, much less is found in the pellicles and it is totally absent
from the cytosol. Its insensitivity to DTT, its selectivity to alkyl-
acetyl-G and its different distribution compared to the enzymic activi
ty involved in PC formation (EC 2.7.8.2) suggest that a different enzy
me, specific for PAF formation (EC 2.7.8.16) via the de novo pathway e
xists in the protozoan.