PRODUCTION OF 7-DEOXY-OKADAIC ACID BY A NEW CALEDONIAN STRAIN OF PROROCENTRUM LIMA (DINOPHYCEAE)

7-Deoxy-okadaic acid and okadaic acid were identified as the major diarrhetic shellfish poisoning (DSP) toxins produced by a New Caledonian strain of Prorocentrum lima Ehrenberg. Dinophysistoxin-1 was not produced by this strain. The cellular concentrations of 7-deoxy-okadaic acid were about one tenth that of okadaic acid and were maximal (∼1.4 pg·cell ^{− 1}) during the stationary growth phase of batch culture. Autolytic hydrolysis of cell extracts did not increase the concentrations of 7-deoxy-okadaic acid, whereas okadaic acid production increased more than 4-fold, indicating that 7-deoxy-okadaic acid, unlike okadaic acid, is not directly derived from large sulfated precursors. 7-Deoxy-okadaic acid could be detected by liquid chromatography-selected reaction monitoring mass spectrometry, HPLC-fluorescence detection after derivatization with 9-anthryldiazomethane (ADAM), and inhibition of protein phosphatases. The solvent washes currently used for solid-phase clean-up of ADAM-derivatized DSP samples elute derivatized 7-deoxy-okadaic acid, indicating that the current sample clean-up protocol for HPLC-fluorescence detection would miss any contamination by this toxin.     

Light-dependent incorporation of selenite and sulphite into selenocysteine and cysteine by isolated pea chloroplasts

Illuminated intact pea chloroplasts in the presence of O-acetylserine (OAS) catalysed incorporation of SeO₃^2- and SO₃^2- into selenocysteine and cysteine at rates of ca 0.36 and 6 μmol/mg Chl per hr respectively. Sonicated chloroplasts catalysed SeO₃^2- and SO₃^2- incorporation at ca 3.9 and 32% respectively of the rates of intact chloroplasts. Addition of GSH and NADPH increased the rates to ca 91 and 98% of the intact rates, but SeO₃^2- incorporation under these conditions was essentially light-independent. In the absence of OAS, intact chloroplasts catalysed reduction of SO₃^2- to S^2- at rates of ca 5.8 μmol/mg Chl per hr. In the presence of OAS, S^2- did not accumulate. Glutathione (GSH) reductase was purified from peas and was inhibited by ZnCl₂. This enzyme, in the presence of purified clover cysteine synthase, OAS, GSH and NADPH, catalysed incorporation of SeO₃^2- into selenocysteine (but not SO₃^2- into cysteine). The reaction was inhibited by ZnCl₂. Incorporation of SeO₃^2- into selenocysteine by illuminated intact chloroplasts and sonicated chloroplasts (with NADPH and GSH) was also inhibited by ZnCl₂ but not by KCN. Conversely, incorporation of SO₃^2- into cysteine was inhibited by KCN but not by ZnCl₂. It was concluded that SeO₃^2- and SO₃^2- are reduced in chloroplasts by independent light-requiring mechanisms. It is proposed that SeO₃^2- is reduced by light-coupled GSH reductase and that the Se^2- produced is incorporated into selenocysteine by cysteine synthase.     

New method for assessing boron status of the oil palm

Plant and Soil - The measurement of optical density of acid hydrolysed oil palm leaves provides the basis for a quantitative determination of the cyanidin liberated. This in turn was shown to be...     

Reversible protein kinase activation of hormone-sensitive lipase from chicken adipose tissue

Hormone-sensitive lipase partially purified from adipose tissue of laying hens was markedly activated by cyclic AMP-dependent protein kinase. Activation was approximately 4-fold (ranging up to as great as 10-fold) compared with the much lower degree of activation obtained with analogous preparations from rat and human adipose tissues (59 and 86%, respectively). The partially purified preparations contained adequate endogenous protein kinase activity to effect complete activation with addition of cyclic AMP, ATP, and Mg(2+). Activation was blocked by protein kinase inhibitor (from rabbit skeletal muscle) but could be restored fully by addition of excess exogenous protein kinase (from bovine skeletal muscle). The fully activated lipase was slowly deactivated by dialysis at 4 degrees C and then rapidly and almost fully reactivated by addition of cyclic AMP and ATP-Mg(2+). Reactivation was blocked by protein kinase inhibitor. This deactivation-reactivation cycle was rapid at 23 degrees C with dialysis against charcoal and could be demonstrated repeatedly using a single preparation. The reversible deactivation of protein kinase-activated enzyme is presumed to reflect the action of a lipase phosphatase. Lipase prepared from tissue previously exposed to glucagon yielded a much smaller degree of activation than lipase prepared from tissue not exposed to the lipolytic hormone, indicating that the physiological hormone-induced activation is probably similar to or identical with the protein kinase activation demonstrated in the cell-free preparations. Under the conditions of assay used, the partially purified lipase fraction contained diglyceride, monoglyceride, and lipoprotein lipase activities. However, treatment with cyclic AMP-dependent protein kinase had virtually no effect on these lipase activities.     

Kompartimentierung und Eigenschaften der MDH-Isoenzyme aus Wassermelonenkeimblättern

Summary Five MDH-isoenzymes (I–V) from cotyledons of dark-grown water-melon seedlings older than 2 days can be identified by disc-electrophoresis. By isolating and fractionating cell organelles (10000 g fraction) by density gradient centrifugation (Fig. 1) the following compartmentation of the MDH-isoenzymes can be shown: the mitochondria contain isoenzyme III and the glyoxysomes preponderantly (if not exclusive) isoenzyme V (Fig. 2), whereas the isoenzymes I, II, and IV belong to the cytosol.The 5 MDH-isoenzymes differ in several properties, e.g. differential precipitation by ammonium sulfate (Fig. 4) or isoelectric point (Fig. 5). The glyoxysomal MDH is a relatively basic protein (isoelectric point at pH 8.7), whereas the isoelectric points of the other isoenzymes lie between pH 6.4 (IV) and pH 4.7 (I).