Reference

In vitro studies on pathways and regulation of electron transport to nitrogenase with a cell-free extract from heterocysts of Anabaena variabilis

In vitro studies on pathways and regulation of electron transport to nitrogenase with a cell-free extract from heterocysts of Anabaena variabilis. Schrautemeier, Bernhard; Boehme, Herbert; Boeger, Peter (Univ. Konstanz, Konstanz D-7750, Fed. Rep. Ger.). Arch. Microbiol., 137(1), 14-20 (English) 1984. CODEN: AMICCW. ISSN: 0302-8933. DOCUMENT TYPE: Journal CA Section: 11 (Plant Biochemistry) A cell-free prepn. of heterocysts from A. variabilis showed high nitrogenase activities with several physiol. electron donors, dependent on addn. of an ATP-generating system. Light-induced acetylene redn. with the artificial electron donor to photosystem I, diaminodurol, exhibited the same light satn. as with H as donor. Inhibitors of electron flow through plastoquinone affected light-induced, H- or NADH-dependent nitrogenase activity in a similar way. Several uncoupling agents were without effect, indicating that energized membranes are not a prerequisite for N fixation. Thus, NADH or H deliver electrons to nitrogenase via photosystem I and ferredoxin, feeding in at the plastoquinone site. In the light, addn. of NADP induced a lag in H- or NADP-supported acetylene redn. , apparently by competing with nitrogenase for electrons at the reducing side of photosystem I. Time reversal of this inhibition reflects a regulation of photosystem I-dependent nitrogenase activity by the NADPH/NADP ratio in the cell. This was directly demonstrated by differently adjusted NADPH/NADP ratios. NADPH donates electrons to nitrogenase in the dark and in the light, the light reaction being DBMIB-sensitive. NADPH-supported acetylene redn. was inhibited by NADP. This inhibition was not reversed with time, pointing to an involvement of ferredoxin: NADP oxidoreductase (EC 1.18.1.2) in this pathway. Apparently, in the dark, this enzyme is able to directly reduce ferredoxin, whereas in the light, electrons from NADPH first have to pass through photosystem I before reducing ferredoxin, hence nitrogenase. Intermediates of glycolysis, like glucose 6-phosphate, fructose 1,6-bisphosphate, and dihydroxyacetone phosphate supported nitrogenase activity in the dark, each with catalytic amts. of both NAD and NADP as equally effective cofactors. In heterocysts, electrons for N fixation apparently are essentially supplied by dark reactions, mainly by glycolysis. NADH (and H) contribute electrons via photosystem I in the light, whereas the NADPH/NADP ratio regulates linear and cyclic electron flow at the reducing side of photosystem I to provide a ratio of ATP/electrons most effective for nitrogenase.Except for chemicals metioned above, 77-92-9 and 3102-87-2 are also used. .

Plasma citrate in relation to glucose and free fatty acid metabolism in man

Plasma citrate in relation to glucose and free fatty acid metabolism in man. Nielsen, Torsten Toftegaard (Dep. Cardiol., Aarhus Kommunehosp., Aarhus DK-8000, Den.). DMB, Dan. Med. Bull., 30(6), 357-78 (English) 1983. CODEN: DDMBDK. ISSN: 0011-6092.In this experiment, several chemicals are used like 50-99-7 and 77-92-9 DOCUMENT TYPE: Journal; General Review CA Section: 13 (Mammalian Biochemistry) A review with many refs. .