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Extracts of ripening olive fruits (Olea europaea L. cv. Kalamata) ‐were analyzed for the presence of lipoxygenase activity and for the content of phenolic compounds, which are lipoxygenase inhibitors. Two distinct lipoxygenase activities were identified by their pH optima and sensitivity to the inhibitor nordihydroguaiaretic acid (NDGA). Both activities were low during early ripening stages, and increased sharply between 57 and 94 days postanthesis, reaching a plateau at about 120 days. The content of phenolic compounds, mainly oleuropein, changed in the opposite way, suggesting their involvement in the regulation of the two lipoxygenase activities during the olive fruit development. The two lipoxygenase activities could have a role in fruit maturation and senescence.

The effects of a glyceroethanolic macerate of the leaves of Olea europaea L. and of oleuropein on excito-conduction and on the right atrial and ventricular monophasic action potential (MAP) have been studied in anaesthetized dogs using the technique of endocavitary recording. At the higher doses tested, a slight increase in the sinusal cycle of the sinoatrial conduction time and of the sinus node recovery time, together with a prolongation of the atrioventricular and intraventricular conduction and an increase of the atrial and ventricular MAP duration were observed. This may be due to a decrease in the repolarization phase 3. These electrophysiological effects indicate an inhibitory action both on the swift influx of sodium and on the slow influx of calcium, as well as a decrease in potassium conductance.

Treatment of ornithine carbamoyltransferase from dolphin Stenella with pyridoxal phosphate, followed by reduction with NaBH,, resulted in complete loss of enzyme activity. The phosphate alone or the substrate analogue 2-aminovaleric acid moderately decreased the extent of inactivation, while carbamoyl phosphate plus 2-aminovaleric acid provided complete protection from inactivation. The partially inactivated enzyme showed K,, values for substrates equivalent to those of native enzyme and lowered k,,, values. Two lysyl residues were substantially modified in the absence of ligands but only one of them was responsible for the inactivation of catalytic activity. Modification of a single subunit was sufficient to completely abolish the catalytic activity of the trimeric enzyme. The lysine involved has been identified as lysine 56 on the known primary structure of homologous human liver enzyme.

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