3 -adenosine-5 -phosphosulphate

Various thioated and selenoated nucleotides have been synthesised and some of these, for example, (10.118) are known to be involved in biochemical reactions. The adenosine 5 phosphosulphate (10.118c) (base = adenine), for example, is involved in sulphate metabolism (11.105)... 

Higher plants and many microorganisms utilise sulphate as their source of sulphur. The initial step in sulphate assimilation involves the action of ATP on sulphate ions to give adenosine-5 -phospho-sulphate (APS). Further phosphorylation by ATP and sulphurylase then occurs and 3 -phospho-adenosine-5 -phosphosulphate (PAPS) is formed. 

Sulphatide is an important constituent of the myelin sheath of nervous tissue and the incorporation of radioactive sulphate into the sulphatide molecule has been used to study myelination. The donor of the sulphate group is the complex nucleotide 3 -phosphoadenosine 5 -phosphosulphate, usually abbreviated in scientific papers to PAPS (Figure 7.10). PAPS itself is produced from ATP in two steps via an adenosine 5 -phosphosulphate (APS) intermediate. The synthesis of sulphatide is catalysed by a sulphotransferase which has been detected in the microsomal fraction from a number of tissues ... 

The reactions leading to the formation of active sulphate were elucidated in enzyme fractionation studies on baker s yeast. It is a two-step process leading first to the formation of adenosine-5 -phosphosulphate (APS) and then to the active sulphate , 3 -adeno-sine-5 -phosphosulphate (PAPS) thus ... 

P = high energy phosphate bond PAL = phenylalanine ammonia lyase PAPS = 3 -adenosine-5 -phosphosulphate Pi = inorganic orthophosphate PPi = inorganic pyrophosphate PEP = phosphoenolpyruvate... 

Figure 11.19 Sulpholipid synthesis and breakdown. Continuous lines show reactions that have been demonstrated dashed lines are possible pathways. Underlined compounds have been used in experiments on sulpholipid synthesis. APS, adenosine phosphosulphate PAPS, phosphoadenosine phosphosulphate. Adapted from Harwood (19806).

As expected the formation of sulphatides involves transfer of sulphate from phosphoadenosine phosphosulphate (PAPS). The latter is formed in a two-step reaction involving ATP and inorganic sulphate via an adenosine phosphosulphate (APS) intermediate. Galactosylceramide and lactosyl-ceramide were both acceptors for the sulphate from PAPS. Sulphatide synthesis is most rapid in the period 20-25 days after birth in rat brain (Stoffel, 1971). The sulphatides may be involved in the activity of the Na /K -ATPase (cf. Stoffel, 1971). 

Figure 1 Phase I and Phase II metabolic pathways. PAPS, adenosine 3 -phosphate S -phosphosulphate UDPGA, uridine diphosphate glucuronic acid.

R9. Robbins, P. W., and Lipmann, F., Identification of enzymatically active sulphate as adenosine-3 -phosphate-5 -phosphosulphate. J. Amer. Chem. Sac. 78, 2652-2653 (1956). 

The likely sulphate donor for all of these glycolipids is phosphoadenosyl phosphosulphate (adenosine 3 -phosphate 5 -phosphosulphate), which is known to be the physiological donor for Gl-lbS. In the synthesis of GL-lbS sulphate transfer and galactosyl transfer are coupled it is probable that different sulphotransferases act in producing the other sulphoglycolipids. 

PAP = adenosine 3, 5 -diphosphate PAPS = adenosine 3 -phosphate 5 -phosphosulphate)... 

Sulphate conjugates, once called ethereal sulphates because of their extraction characteristics, are of two major types aryl or alkyl sulphates (which are esters of phenols or alcohols) and steroid sulphates. The sulphate moiety is transferred from the cofactor adenosine-3 -phosphate-S -phosphosulphate (PAPS) to an acceptor by enzymes known as sulphotransferases or sulphokinases. The enzymes which catalyse the formation of PAPS as well as the sulphokinases are in the soluble fraction of liver ... 

The terminal step, O-sulphonation of desulphobenzylglucosinolate (90), is catalysed by a sulphotransferase, isolated from T. majus, utilizing 3 -phospho-adenosine S -phosphosulphate (PAPI as the sulphate donor and possessing very little specificity for the type of desulphoglucosinolate used as the substrate. IWs finding calls for caution, in addition to that previously ex-... 

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