Ecdysteroids: isolation,chemical transformations,and biological activity

Phytochemistry Reviews - Ecdysteroids are polyhydroxylated sterols, and are widespread in the plant and animal world. To date, over 520 ecdysteroids have been isolated from natural sources. The...     

Physicochemical,catalytic, and regulatory properties of malate dehydrogenase from Rhodovulum steppense bacteria,strain A-20s

The physicochemical, regulatory, and kinetic properties of malate dehydrogenase (EC 1.1.1.37) from haloalkaliphilic purple nonsulfur Rhodovulum steppense bacteria, strain A-20s, were studied. The malate dehydrogenase (MDH) preparation with a specific activity of 3.775 ± 0.113 U/mg protein was obtained in an electrophoretically homogeneous state using multistep purification. Using homogenous preparations, the molecular weight and the Michaelis constant of the enzyme were determined; the effects of metal ions, the temperature effect, and the thermal stability of the MDH were studied. The dimer structure of the enzyme was demonstrated by DS-Na-electrophoresis.     

Phosphorylation-dependent stimulation of prostanoid synthesis by nigericin in cerebral endothelial cells

Nigericin decreases intracellular pH(pH_i) and stimulates prostanoid(PG) synthesis in endothelial cells from cerebral microvessels ofnewborn pigs. Nigericin-induced PG production was abolished by proteintyrosine kinase (PTK) inhibitors and amplified by phorbol 12-myristate13-acetate (PMA) or protein tyrosine phosphatase (PTP) inhibitors.Nigericin-induced PG production in PMA-primed cells was potentiated byPTP inhibitors and abrogated by PTK inhibitors. PhospholipaseA₂(PLA₂) activity was stimulatedby nigericin in a phosphorylation-dependent manner. Nigericin'seffects on PG production and PLA₂activity were reproduced by ionomycin, which activates cytosolicPLA₂(cPLA₂).cPLA₂ was immunodetected in endothelial cell lysates. We found no evidence that nigericin's effects are mediated via mitogen-activated protein (MAP) kinase [extracellularly regulated kinase 1 (ERK1) and ERK2]activation: although nigericin stimulateddetergent-soluble MAP kinase, its effects were not amplified by PMA orPTP inhibitors. Phosphorylation-dependent stimulation of PG synthesiswas also observed when pH_i wasdecreased by sodium propionate or a high level ofCO₂. Altogether, our data indicatethat nigericin and decreased pH_istimulate PG synthesis by a protein phosphorylation-dependent mechanisminvolving cross talk between pathways mediated by PTK and PTP and byprotein kinase C; cPLA₂ appears tobe a key enzyme affected by nigericin and decreasedpH_i.

     

on the vertical distribution of microorganisms in lake baikal during spring deep-water renewal

The vertical distribution of microorganisms during spring deep-water renewal in Lake Baikal was studied. The downward advection of trophogenic waters was found to create conditions for the extensive growth of microorganisms capable of decomposing and mineralizing organic carbon, nitrogen, and phosphorus in deep water layers. These processes occur annually at spring thermal bars near the underwater slope of Lake Baikal, whereas in its pelagic zone, the deep intrusions of waters rich in organic material are observed only in the years when enhanced deep-water renewal is accompanied by a high spring yield of phytoplankton.