Sulfur delivery

Three NifS-like proteins, IscS, CSD, and CsdB, from E. coli catalyse the removal of sulfur and selenium from L-cysteine and L-selenocysteine, to form L-alanine. These enzymes are proposed to function as sulfur-delivery proteins for iron-sulfur clusters, thiamin, 4-thiouridine, biotin, and molybdopterin. Mihara et alP have reported evidence that a strain lacking IscS is incapable of synthesiz-... 

Prior reports have demonstrated the transfer of iron from holo frataxin to nucleation sites on ISU as a prerequisite step for [2Fe-2S] cluster formation on ISU 10), The time course of the cluster assembly reaction is conveniently monitored from the 456 nm absorbance of holo ISU formed during the [2Fe-2S] cluster assembly reaction (Figure 4). A kinetic rate constant A obs 0.126 min was determined with 100 pM ISU, 2.4 mM Na2S, and 40 pM holo frataxin in 50 mM Hepes buffer (pH 7.5) with 5 mM DTT. Similar rates were obtained for IscS/Cys-mediated sulfur delivery, consistent with iron release from frataxin as a rate-limiting step in the cluster assembly reaction. 

Alternatives to coal and hydrocarbon fuels as a source of power have been sought with increasing determination over the past three decades. One possibility is the Hydrogen Economy (p, 40), Another possibility, particularly for secondary, mobile sources of power, is the use of storage batteries. Indeed, electric vehicles were developed simultaneously with the first intemal-combustion-cngined vehicles, the first being made in 1888. In those days, over a century ago, electric vehicles were popular and sold well compared with the then noisy, inconvenient and rather unreliable peU ol-engined vehicles. In 1899 an electric car held the world land-speed record at 105 km per hour. In the early years of this century, taxis in New York, Boston and Berlin were mainly electric there were over 20000 electi ic vehicles in the USA and some 10000 cars and commercial vehicles in London. Even today (silent) battery-powered milk delivery vehicles are still operated in the UK. These use the traditional lead-sulfuric acid battery (p. 371), but this is extremely heavy and rather expensive. 

The basic price of coal at the pit is based on the coal gross calorific value, with allowances then made for the ash, sulfur and chlorine contents. The haulage charges depend on the distance from the pit to the site and on the method of delivery. Tipper-vehicle deliveries are cheaper than conveyor vehicles which, in turn, are cheaper than the pneumatic (blower) vehicles. The method of delivery will obviously be decided by a combination of space and cleanliness factors. In the case of certain customers, special agreements may be available at special rates where the annual coal consumption is large and the supplier wishes to retain the market. 

This actually doesn t work well. Recall (Chapter 10) that nucleophilicity is dependent on polarizability (the size of the atom). Large atoms (like sulfur or iodine) are very polarizable, and therefore, they are excellent nucleophiles. Small atoms are not polarizable, and they make poor nucleophiles. H is as small as they come, and therefore H is not a great nucleophile. H is a good base (in fact, it is an excellent base), but it is not a good nucleophile. So, we use LAH or NaBH4 as a source of nucleophilic H . We can think of LAH and NaBH4 as delivery agents of nucleophilic H. ... 

Pickard, P., Sulfur-iodine thermochemical cycle, 2006 Annual Merit Review Proc., Hydrogen Production and Delivery, D. Nuclear Energy Initiative, http //www.hydrogen.energy.gov/ annual review06 delivery.html. 

Now, in the summer of 1939, orders went out from Krauch s office in an unbelievably increasing stream. First, to the Vermin-lungstelle Wehrmacht. From there, orders for nitrates went by special delivery to Dr. Ambros at Ludwigshafen. From Ludwigs-hafen the nitrates were shipped to the Dynamit A.G. s older factories. The Haber-Bosch nitrates went to the largest factories at Pressburg and Troisdorf, the nitrates weaned from sulfuric acid to Mannheim and Hackenburg. 

The mechanism and sequence of events that control delivery of protons and electrons to the FeMo cofactor during substrate reduction is not well understood in its particulars.8 It is believed that conformational change in MoFe-protein is necessary for electron transfer from the P-cluster to the M center (FeMoco) and that ATP hydrolysis and P release occurring on the Fe-protein drive the process. Hypothetically, P-clusters provide a reservoir of reducing equivalents that are transferred to substrate bound at FeMoco. Electrons are transferred one at a time from Fe-protein but the P-cluster and M center have electron buffering capacity, allowing successive two-electron transfers to, and protonations of, bound substrates.8 Neither component protein will reduce any substrate in the absence of its catalytic partner. Also, apoprotein (with any or all metal-sulfur clusters removed) will not reduce dinitrogen. 

Detailed photochemical studies of RBS and RRS have revealed that the photolysis of RRS produces RBS and NO quantitatively (Scheme 5.6) and the RBS produced undergoes further photodecomposition to generate NO and iron (III) [165, 168]. RBS has been tested as an NO delivery drug to the vascular and brain tissues by thermal as well as photochemical means [169, 170]. Due to the high solubilities in aprotic solvents, Roussin s salts are able to penetrate the endothelial cell membrane easily and deliver NO for hours [169]. RBS has been found to inhibit ADP-induced platelet aggregation [171] and Roussin s salts in general show a bacteriostatic effect, presumably due to the interaction of released NO and iron-sulfur proteins [172]. 

The mother liquor from seaweed ash contains quite a large quantity of a very peculiar and curious substance it is easily extracted one merely pours sulfuric acid on the mother liquor and heats the mixture in a retort the mouth of which is connected to a delivery-tube leading to a bulb. The substance which is precipitated in the form of a black, shining powder immediately after the addition of sulfuric acid, rises, when heated, in vapor of a superb violet color. This vapor condenses in the delivery-tube and receiver in the form of very brilliant crystalline plates having a luster equal to that of crystalline lead sulfide. Upon washing these plates with a little distilled water, one obtains the substance in the pure state (45, 23). 

Sixty grams of bromine, previously dried with concentrated sulfuric acid are placed in a small dropping funnel with a long delivery tube. The neck of the funnel is protected with a drying tube. 

Forty grains of potassium nitrite and 50g of potassium acetate are dissolved in 100ml of ice-cold water and placed in a one-liter filter flask fitted for the introduction of sulfur dioxide through a delivery tube that leads well into the liquid. Seven hundred and fifty grams of crushed ice are added and sulfur dioxide is passed rapidly into the agitated mixture until absorption is complete. (This is indicated by the fact that the odor of the gas persists after shaking.) The temperature must not rise above 0eC and a small amount of ice should still be present in the reaction mixture when saturation is reached at the end of about one-half hour. 

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