Enzymic sulfation

Sulfotransferases (SULTs) are important for the metabolism of a number of drugs, neurotransmitters, and hormones, especially the steroid hormones. The cosubstrate for these reactions is 3 -phosphoadenosine 5 -phosphosulfate (PAPS) (Fig. 4.1). Like the aforementioned enzymes, sulfate conjugation typically renders the compound inactive and more water soluble. However, this process can also result in the activation of certain compounds, such as the antihypertensive minoxidil and several of the steroid hormones. Seven SULT isoforms identified in humans, including SULTs lAl to 1A3, possess activity toward phenolic substrates such as dopamine, estradiol, and acetaminophen. SULTIBI possesses activity toward such endogenous substrates as dopamine and triiodothyronine. SULTIEI has substantial activity toward steroid hormones, especially estradiol and dehydroepiandrosterone, and toward the anti-... 

As already mentioned (see p. 470), it is probable that sulfation of the carbohydrate chains occurs, to a considerable extent at least (if not wholly), after the polymerization has occurred. This probability was suggested by Meyer and coworkers,351352 because of their finding of chondroitin in ox cornea that was free from, or very low (<2%) in, sulfate this substance was later shown to be enzymically sulfated by extracts of the isthmus of hen oviduct at a higher rate than all other substances assayed.353... 

Also reactions with quiones and a -unsaturated compounds. b Enzymic sulfate and sulfite reductions reductant requirement equivalent to 4NADPH + 4H+. 

The ability of insect sulfotransferases to catalyze the sulfation of plant and insect steroids may simply reflect the broad substrate specificity of the enzymes. On the other hand, it may be indicative of a more important physiological function of the enzymes. Sulfate esters of cholesterol, campesterol and e-sitosterol have been identified in the meconium of tobacco hornworm (M. sexta) pupae ( ), and these steroids are known precursors of a-and e-ecdysone and other molting hormones in this species ( ). Further, there is evidence that houseflies (M. domestica) and diapausing pupae of M. sexta convert 22,25 bisdeoxyecdysone, a-ecdysone and 20-hydroxyecdysone into sulfate and glucoside conjugates ( ). 

Enzymic sulfation, with 3 -0-phosphonoadenylyl sulfate, of the 3-hydroxyl group of the D-galactopyranose residue of the cerebrosides obtained led to the sulfatides.58,59... 

The origin of the sulfuric acid group of the galactan is not known. However, in this connection, it is of interest to compare the structure of active sulfate (adenylyl sulfate 3 -phosphate), which is known to be a sulfate donor, " with that of the adenosine 3, 5 -pyrophosphate discovered in Porphyra perforata The adenosine 3, 5 -pyrophosphate in this alga may possibly activate the inorganic sulfate, causing the formation of active sulfate, which then eflFects the enzymic sulfation of the polysaccharide. 

The hypothesis that the repeating units are sulfated as soon as they are added to the growing polysaccharide chain would be attractive in the cell-free system, however, sulfation seems to occur on preformed polysaccharides as readily as on polysaccharide chains in the process of elongation. In any event, sulfation of such polysaccharides as heparin must be a complex process, as sulfete groups are transferred to several diflFerent positions on the disaccharide repeating unit. The enzymic sulfation of the amino group was found to be accompanied by simultaneous release of free acetate groups from the heparin precursor. ... 

Macrides, T.A., Faktor, D.A., Kalafatis, N., and Amiet, R.G. (1994) Enzymic sulfation of bile salts. Partial purification and characterization of an enzyme from the liver of the shark Heterodontus portusjacksoni that catalyses the sulfation of the shark bile steroid 5 3-scymnol. Comp. Biochem. Physiol., 107B, 461-469. 

Metabolic Functions. Manganese is essential for normal body stmcture, reproduction, normal functioning of the central nervous system, and activation of numerous enzymes (126). Synthesis of the mucopolysaccharide chondroitin sulfate involves a series of reactions where manganese is required in at least five steps (127). These reactions are responsible for formation of polysaccharides and linkage between the polysaccharide and proteins that form... 

Molybdate is also known as an inhibitor of the important enzyme ATP sulfurylase where ATP is adenosine triphosphate, which activates sulfate for participation in biosynthetic pathways (56). The tetrahedral molybdate dianion, MoO , substitutes for the tetrahedral sulfate dianion, SO , and leads to futile cycling of the enzyme and total inhibition of sulfate activation. Molybdate is also a co-effector in the receptor for steroids (qv) in mammalian systems, a biochemical finding that may also have physiological implications (57). 

Purification. Enzyme purity, expressed in terms of the percent active enzyme protein of total protein, is primarily achieved by the strain selection and fermentation method. In some cases, however, removal of nonactive protein by purification is necessary. The key purification method is selective precipitation of the product or impurities by addition of salt, eg, sodium sulfate, or solvent, eg, ethanol or acetone by heat denaturation or by isoelectric precipitation, ie, pH adjustments. Methods have been introduced to produce crystalline enzyme preparations (24). 

Enzymes for Liming and Bating. An important discovery (79) for the leather industry was the close relationship between the amount of dermatan sulfate removed and the degree of opening up. Until this discovery, the use of enzymes during the liming and unhairing steps was not considered worthwhile. 

Prior to the bating process, the hides are delimed with ammonium sulfate and/or ammonium chloride. Proteases are then appUed. The early preparation proposed by Rn hm was pancreatic trypsin. The use of a bating enzyme makes the hides soft and supple to prepare them for tanning. A new microbial protease, Pyrase 250 MP (82) (Novo Nordisk A/S) has been found to be a promising substitute for pancreatic trypsin [9002-07-7] which is more expensive because it must be extracted from pancreatic glands. 

Fig. 10. Pharmacophores for angiotension-converting enzyme. Distances in nm. (a) The stmcture of a semirigid inhibitor and distances between essential atoms from which one pharmacophore was derived (79). (b) In another pharmacophore, atom 1 is a potential zinc ligand (sulfhydryl or carboxylate oxygen), atom 2 is a neutral hydrogen bond acceptor, atom 3 is an anion (deprotonated sulfur or charged oxygen), atom 4 indicates the direction of a hydrogen bond to atom two, and atom 5 is the central atom of a carboxylate, sulfate, or phosphate of which atom 3 is an oxygen, or atom 5 is an unsaturated carbon when atom 3 is a deprotonated sulfur. The angle 1- -2- -3- -4 is —135 to —180° or 135 to 180°, and 1- -2- -3- -5 is —90 to 90°.

The sulfate is obtained by evaporating the aqueous layer in vacuo. The hydrochloride can be obtained in the same way but using HCl instead of H2SO4. SAM-HCl has a solubility of 10% in H2O. The salts are stable in the cold at pH 4-6 but decompose in alkaline media. [Cantoni Biochem Prep 5 58 1957.] The purity of SAM can be determined by paper chromatography [Cantoni J Biol Chem 204 403 1953 Methods Enzymol 3 601 1957], and electrophoretic methods or enzymic analysis [Cantoni and Vignos J Biol Chem 209 647 1954]. 

Figure 18.4 The hanging-drop method of protein crystallization, (a) About 10 pi of a 10 mg/ml protein solution in a buffer with added precipitant—such as ammonium sulfate, at a concentration below that at which it causes the protein to precipitate—is put on a thin glass plate that is sealed upside down on the top of a small container. In the container there is about 1 ml of concentrated precipitant solution. Equilibrium between the drop and the container is slowly reached through vapor diffusion, the precipitant concentration in the drop is increased by loss of water to the reservoir, and once the saturation point is reached the protein slowly comes out of solution. If other conditions such as pH and temperature are right, protein crystals will occur in the drop, (b) Crystals of recombinant enzyme RuBisCo from Anacystis nidulans formed by the hanging-drop method. (Courtesy of Janet Newman, Uppsala, who produced these crystals.)...

Mammalian sulfite oxidase is the last enzyme in the pathway for degradation of sulfur-containing amino acids. Sulfite oxidase (SO) catalyzes the oxidation of sulfite (SO ) to sulfate (S04 ), using the heme-containing protein, cytochrome c, as electron acceptor ... 

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