PREPARATION AND CHARACTERIZATION OF SUBCELLULAR-FRACTIONS SUITABLE FOR STUDIES OF XENOBIOTIC METABOLISM FROM LEAF SHEATHS OF A MARINE SEAGRASS - POSIDONIA-OCEANICA (LINNAEUS) DELILE

The capacity of the mammalian liver microsomal P-450- dependent system s to metabolize a wide variety of endogenous and exogenous compounds i s thought to reflect the presence of multiple forms of P-450 haemoprot eins with broad and overlapping substrate specificity. In plants, the functions and specificity of cytochrome P-450 systems are less well kn own. This study was designed to prepare and characterize subcellular f ractions from fresh sheaths (basal parts of leaves) of a mediterranean seagrass Posidonia oceanica (Linnaeus) Delile, the aim being the prep aration of a microsomal fraction suitable for studying xenobiotic meta bolism. The purity of the different fractions obtained by centrifugati on, as well as the recovery of different organelles, was determined us ing enzyme markers (cytochrome c oxidase, alkaline phosphatase, glucos e-6-phosphatase) and morphological examination by transmission electro n microscopy. Some assays of enzymes involved in xenobiotic metabolism (cytochrome c reductase, laurate hydroxylase, ethoxyresorufin O-deeth ylase and glutathione-S-transferase) were also performed on different fractions of the preparation. The subcellular distribution for drug me tabolism and marker enzymes showed a loss of endoplasmic reticulum in the pellet obtained after the first centrifugation, but the microsomal fraction was relatively free of mitochondria and fragments of the pla sma membrane. Some assays are still being performed to avoid the small loss of endoplasmic reticulum experienced with the first pellet. Howe ver, the microsomes prepared in this study from sheaths of Posidonia o ceanica appear suitable for further investigation of xenobiotic metabo lism.