Xylose 5-phosphate, synthesis

All the enzymes of the hexose monophosphate shunt have been found in the supernatant fraction of the cell. The enzymes of the glucuronic pathway, with the exception of NADP-L-hexonate dehydrogenase and aldonolactonase, which are found in the supernatant fraction of the cell, have a complex intracellular distribution. All the enzymes involved in glucuronic acid-1-phosphate synthesis and in the conversion of glucuronic phosphate or glucuronic acid to L-xylose or ascorbic acid are associated with the endoplasmic reticulum. The enzymes involved in the conversion of L-xylose to D-xylose are found in mitochondria. Thus, the complete glucuronic pathway involves three different cell fractions. 

Scheme 5.58. (a) TK catalyzed synthesis of D-xylose-5-phosphate from D-fructose-bisphosphate... 

Another hypothesis describing the mode of action of ACTH has recently gained some support. It proposes that ACTH modifies cellular permeability through the intermediate of adenosine-3, 5 -mono-phosphate. The increased penetration of xylose and a-aminoisobutyric acid under the influence of ACTH has been established. It also has been proposed that ACTH stimulates the formation of cyclic adenylate, which in turn induces the synthesis of new mitochondrial proteins. The appearance of the new protein is associated with the development of activity of the enzyme involved in the conversion of cholesterol to pregnenolone. 

A simple enzymic synthesis of barium glucose 6-phosphate from starch has appeared. Ths use of 2-methylthio-4 -l,3,2-benzodioxaphosphorin-2-oxide (MTBO) (see M. Eto et al.. Tetrahedron Letters, 1971, 4263) continues to receive attention. A study of twenty amines as catalysts has shown that primary n-alkyl and alicyclic amines are the most effective, followed by secondary and tertiary amines. Increasing the branching reduced the catalytic efficacy while cyclic imines gave low yields. MTBO has been used to synthesize adenosine 2, 3 -cyclic phosphate in 50% yield from 5 -0-acetyladenosine (Scheme 5). o-Arabinose 5-phosphate and o-xylose 5-phosphate have been... 

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