Sulfate-transfer enzymes

Metal Ion Effects. The metal ion effects on the acid-catalyzed hydrolysis of PPS also were examined by Benkovic and Hevey (5). However, they observed that in water near pH 3, the rate enhancement in the presence of an excess of metal ion was at most only threefold (Mg2+, Ca2+, Al3+) and in some cases (Zn2+, Co2+, Cu2+) the rate was actually retarded. We thought that the substrate PPS and Mg2+ ion should be hydrated heavily in water so that their complexa-tion for rate enhancement is weak. If, however, the hydrolysis is carried out in a solvent of low water content, such complexation would not occur, and therefore, the rate enhancement might be more pronounced. This possibility appears to be supported by the fact that the active sites of many enzymes are hydrophobic. Of course, there is a possibility that the S—O fission may not require metal ion activation. In this connection, it is interesting to note that in biological phosphoryl-transfer reactions the enzymes generally require divalent metal ions for activity (7, 8, 9), but such metal ion dependency appears to be less important for sulfate-transfer enzymes. For example, many phosphatases require metal ions, but no sulfatase is known to be metal... 

Cerebrosides and sphingomyelin are believed to accumulate in the globoid bodies. In fact, the injection of cerebrosides into rats has led to the appearance in the white matter of cells that resemble globoid cells. The biochemical defect in Krabbe s disease is still unknown, but two clues are available. There are no defects in sphingomyelin breakdown, there is a shift in the ratio of cerebrosides to sulfatides (from 3 to 1 in the normal individuals to 12 to 1 in those with leukodystrophy. These observations have led to the suggestion [127-130] that the lipidosis results from a deficiency of a sulfate-transferring enzyme (see Fig. 3-43). 

Phosphosulfates may react with a nucleophile (Nu) in either of the two modes of P-O or S-O bond fission (Figure 2). If water is the nucleophile, both modes of fission result in the same hydrolysis products. Mechanistically, however, the enzymes that catalyze P—O fission may be regarded as phosphatases, while those that catalyze S—O fission are sulfohydrolases. In fact, many hydrolytic enzymes are assumed to be sulfohydrolases without mechanistic proof. The possibility that they might be phosphatases was suggested by Roy by taking account their metal ion dependency (4). Meanwhile, PAPS acts as the sulfate donor to numerous nucleophilic acceptors such as steroids and phenols. In such sulfate transfer reactions, S—O fission must occur. PAPS and APS also are known to act as the key intermediates in the reduction of sulfate to sulfite. Here again, the S—O fission may be the most probable mode. 

Baddiley et at. used the reagent to convert adenosine 3, 5 -diphosphate into adenosine 3 -phosphate-5 -sulfatophosphate. In the presence of an appropriate enzyme, this active sulfate transfers the sulfate group to a variety of substrates. 

Conjugation of 0-, N- and S-contalnlng functional groups with sulfate Is very common In animal systems. Sulfate Is transferred from adenosine 3 -phosphate-5 -sulfatophosphate (PAPS) by a variety of transfer enzymes. The mechanisms for sulfation of xenobiotics (74,75) and the chemistry of sulfate esters and related compounds and the synthesis of these have been reviewed (75-77). Syntheses of 0-, N- and S-sulfate conjugates of xenobiotics may be carried out by the methods described below. 

It may seem strange that we have left the transfer of sulfur out of this description, but it was available initially as H2S, which diffuses easily, compare H20, and is reactive with metal ions and some organic centres. Sulfur from intermediate states of oxidation of this element, e.g. S2Of, is transferred by molybdenum enzymes. Later, when sulfur became sulfate, a coenzyme (PAPS) was required for its transfer (see aerobes and eukaryotes).)... 

This class constitutes a large set of enzymes that catalyze the transfer of sulfate groups [EC 2.8.2.x]. See also specific enzyme... 

The tyrosine protein sulfotransferase preparations from Golgi-enriched membranes have been used for sulfation of synthetic mono- and multiple-tyrosine peptides related to known sulfation sites in proteins and peptides at analytical levels to establish the enzyme specificities.1f11-13] Preparative sulfations have not been carried out to date. A novel type of arylsulfotransferase produced by Eubacterium A-44 which is part of the human intestinal flora, has recently been discovered.1"1911111 This enzyme catalyzes the transfer of a sulfate group from phenolic sulfate, but not from 3 -phosphadenosine-5 -phosphasulfate, to other phenolic compounds. Using 4-nitrophenylsulfate as a donor substrate and tyrosine-containing peptides and proteins as acceptor substrates it catalyzes the specific sulfation of the tyrosine residues.11111-112 While this enzyme very efficiently sulfates tyrosine derivatives, the... 

Enzymic transfer of D-xylose from uridine 5 -(D-xylopyranosyI-HC pyrophosphate) to L-serine residues of endogenous protein acceptors from (a) a cell tumor of the mouse188 and (b) chick-embryo cartilage189 occurs in cell-free extracts of both of these tissues, in the absence of biosynthesis of protein. The enzyme preparations employed were from the supernatant liquor, although activity was also present in the insoluble fractions. In these two types of tissue, the acceptors are heparin and chondroitin sulfate, respectively, but the presence of other D-xylose-containing glycoproteins in ascites fluid from... 

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