Glucose 6-phosphate dehydrogenase is an NADP-dependent enzyme that converts glucose 6-phosphate to 6-phosphogluconolactone. The later is then hydrolysed by the glucanolactone hydrolase to 6-phosphogluconate. The next reaction involving the synthesis of NADPH is catalysed by 6-phosphogluconate dehydrogenase to produce 3-keto 6-phosphogluconate, which then undergoes decarboxylation to give ribulose 5-phosphate.
The sequence of reactions of HMP shunt is divided into two phases as shown in Figure 8.26.
The enzymes of HMP shunt are located in the cytosol tissues mostly heavily involved in lipid biosynthesis (liver, mammary gland, adipose tissue, adrenal cortex, testis, and erythrocytes).
INTRODUCTION Hexose monophosphate pathway or HMP shunt is also called pentose phosphate or phosphogluconate pathway. This is an alternative pathway of glycolysis and TCA cycle for oxidation of glucose. It does not generate ATP but has the following two major functions:
When sugars react with strong mineral acids, they undergo dehydration and form furfurals. Furfurals condense with phenolic compounds such as α-napthol, thymol, and resorcinol to produce coloured complexes. This property of the sugars helps in the identification of sugars. Note: This test is used for distinguishing between glucose and fructose. If boiled for a long time,…
The rate of respiration (O2 consumption) is tightly regulated in the mitochondria. It is generally regulated by the availability of ADP as a basic substrate for phosphorylation. Depending on the rate of consumption of O2 and also on the availability of Pi acceptor, this kind of control is called acceptor control of respiration. Availability of ADP is…
Reducing Properties Sugars that are oxidised at C-1 are known as reducing sugars. Sugars can react with the chemical agents due to the presence of free carbonyl (aldehyde or ketone) groups. In the alkaline medium, they form enediols, which reduce Cu2+, Ag+, Fe3+, and Bi+3 and oxidise to the corresponding sugar acids. Such sugars are known…
P:O ratio is defined as the number of moles of inorganic phosphate incorporated into organic form per atom of oxygen consumed. Malate-aspartate shuttle P:O ratio = 38 ATP/12 O2 = 3.16Glycerol 3-phosphate shuttle P:O ratio = 36 ATP/12 O2 = 3
The phenomenon of mutarotation appears to be due to the changes of α- and β-forms and vice versa via the straight chain aldo to keto form. It is generally accepted that the mechanism of mutarotation involves opening and closing of the hemiacetal ring structure of monosaccharides to form traces of aldehyde and α- to β-ring…
Explanation Mutarotation means changing of optical rotation. Tamet explained that when a solution of freshly prepared crystalline glucose of α-D-form is observed in a polariscope, its initial specific rotation of +121.1° gradually decreases and finally becomes steady at + 52.5°. If, however, a solution of pure crystals of β-D-glucose is observed in a polariscope, the initial specific…