FLAVOCYTOCHROME B2 ACTIVITY IN SATUREJA HORTENSIS L. LEAVES

Abstract

Satureja hortensis, an annual herb belonging to the Lamiaceae family, has been used since Antiquity in the Mediterranean and Indo-Iranian regions as culinary herb as well as medicinal plant. Although the medicinal value of S. hortensis has been recognized for thousands of years by tradition, and recently by modern experimental procedures, information on the basic aspects of the physiology and enzymology of the plant is only scarcely available. In this study, flavocytochrome b 2 activity was investigated in an extract obtained from S. hortensis leaves. Flavocytochrome b 2 , or L-(+)-lactate ferricytochrome c oxidoreductase (EC.1.1.2.3), is involved in respiration and energy production. It transfers electrons from lactate to cytochrome c (as a physiological electron acceptor) or to other electron acceptors such as potassium ferricyanide. Flavocytochrome b 2 activity was measured in the extract by following spectrophotometrically, at 420 nm, the reduction of potassium ferricyanide in the presence of lactate and EDTA. PH activity profile exhibited one peak at 9.5 and a shoulder at 8.0. Kinetics parameters, determined at pH optima were as follows: a) with lactate as the varied substrate, apparent Km and V max were, respectively, 2.6 mM and 0.5 μM.min -1 .mg prot -1 at pH 8.0, and 6 mM and 0.95 μM.min -1 .mg prot -1 at pH 9.5; b) with potassium ferricyanide as the varied substrate, apparent K m and V max were, respectively, 23 μM and 0.3 μM.min -1 .mg prot -1 at pH 8.0, and 40 μM and 0.65 μM.min -1 .mg prot -1 at pH 9.5. Malate was a competitive inhibitor of the activity with an IC 50 of 13 mM at pH 8.0 and 27 mM at pH 9.5. Electrophoresis of the extract in polyacrylamide gel under non-denaturing conditions revealed two bands after activity staining in the presence of lactate and tetrazolium blue. Data suggest that at least two isoenzymes of flavocytochrome b 2 are present in S. hortensis leaves.