Arsenolysis

This enzyme [EC 2.4.1.7], also known as sucrose gluco-syltransferase, catalyzes the reaction of sucrose with orthophosphate to produce D-fructose and a-D-glucose 1-phosphate. In the forward reaction, arsenate may replace phosphate as the substrate. However, the resulting product is unstable in aqueous solutions. In the reverse reaction, various ketoses and L-arabinose may replace D-fructose. See Arsenolysis... 

This enzyme [EC 6.3.2.25] catalyzes the ATP-dependent religation of L-tyrosine to the C-terminal L-glutamate residue in the detyrosinated a/S-tubulin dimer, yielding ADP, orthophosphate, and the religated tubulin dimer. L-Phenylalanme and 3,4-dehydroxy-L-phenylalanine are also substrates. This is the only known C-terminal peptide bond-forming reaction involving a protein substrate. See also Arsenolysis... 

See specific amidotransferase GLUTAMINE AMINOTRANSFERASE GlutamineiPRPP amidotransferase, AMIDOPHOSPHORIBOSYLTRANSFERASE GLUTAMINE SYNTHETASE ARSENOLYSIS... 

ADDITIVITY PRINCIPLE Thermodynamically unstable intermediate, ARSENOLYSIS... 

MICROTUBULE ASSEMBLY KINETICS TUBULIN TYROSINE LIGASE ARSENOLYSIS Tungsten,... 

Arsenate will replace phosphate in all phospho-rolytic reactions, e.g., in the cleavage of glycogen by glycogen phosphorylase, of sucrose by sucrose phosphorylase, and in the action of purine nucleoside phosphorylase.b Glucose 1-arsenate or ribose-1-arsenate is presumably a transient intermediate which is hydrolyzed to glucose. The overall process is called arsenolysis. Another reaction in which arsenate can replace phosphate is the oxidation of glyceraldehyde 3-phosphate in the presence of P to form 1,3-bisphosphoglycerate ... 

Arsenicals in treatment of syphilis, 597 Arsenite, reaction with thiols 596 Arseno-ribofuranoside 596s Arsenolysis 596... 

Glucose (L-glucose, l-G1c), 161s Glucose 1-arsenate as intermediate in arsenolysis 595... 

Manson and Lampen243 reported that they obtained the phosphorolysis and arsenolysis of hypoxanthine desoxyriboside by enzyme preparations from calf-thymus gland and rat liver. An acid-stable phosphate ester was isolated as a product of phosphorolysis. Results to be outlined suggested that this ester was 2-desoxy-D-ribose 5-phosphate and evidence was obtained for its formation by a mutase type reaction from 2-desoxy-D-ribose 1-phosphate. This evidence was extended and reinforced when Manson and Lampen244 obtained indications for the formation of desoxy-D-ribose 1-phosphate during the phosphorolysis of thymidine. Consequently the conversions outlined may be depicted as shown. 

Arsenolysis of hypoxanthine desoxy-D-riboside resulted in the formation of hypoxanthine and free 2-desoxy-D-ribose.248 Probably the primary product is 2-desoxy-D-ribose 1-arsenate, which decomposes in aqueous media to 2-desoxy-D-ribose and arsenate ions. 

Arsenolysis Cleavage of an arsenate group from a molecule. 

Kline PC, Schramm VL (1993) Purine nucleoside phosphorylase. Catalytic mechanism and transition-state analysis of the arsenolysis reaction. Biochemistry 32 13212—13219... 

There remains model 4, and MacQuarrie and Bernhard 175) have utilized the full-site reactivity by iodoacetamide and half-site reactivity by FAP to provide support for this model. Thus, di(2-furylacryloyl) enzyme was prepared, and the two remaining sites were blocked with iodoacetate. Acyl groups were then removed from this derivative by arsenolysis, and the resulting dialkyl enzyme was tested for stoichiometry with FAP. Only one acyl group could be incorporated into the dialkyl enzyme. This result cannot be explained in terms of an induced asymmetry model, and indeed, can only be explained by a preexisting asymmetry model if there is a subunit rearrangement. In addition, alkylation of the enzyme with varying quantities of iodoacetate, followed by acylation of these derivatives with FAP, showed a 2 1 ratio of alkylation to acylation, independent... 

It has been suggested (70) that NAD acts by facilitating deacylation of the thiol ester, and the later kinetic studies (189) are in agreement with this view. Only NAD analogs which are active in the oxidative phosphorylation reaction will substitute for NAD in the enzyme-catalyzed arsenolysis of DPGA (188) or acetyl phosphate (SO). At higher pH (8.6) an irreversible S to N transfer of acetyl groups occurs. 

Studies have been made of the variation of K and V with pH for the synthetic reaction, and for the phosphorolysis and arsenolysis of amylopectin and glycogen, respectively. Values of pK of groups ionizing in the enzyme and enzyme—substrate complex are shown in Table XIX. 

The mechanism of arsenolysis is thought to be very similar to that of phosphorolysis. It is believed that D-glucosyl arsenate is formed. 

---