In the HMP shunt, hexoses are converted into pentoses, the most important being ribose 5-phosphate. It is useful for the synthesis of nucleic acids (RNA and DNA) and many nucleotides such as ATP, NAD+, FAD, and CoA.

HMP shunt is unique in generating two important products: pentoses and NADPH needed for the biosynthetic reactions and other functions. The sequence of reactions of HMP shunt is divided into two phases as shown in Figure 8.26. Figure 8.26 Hexose Monophosphate Pathway

The non-oxidative reactions are concerned with the inter-conversion of 3−, 4−, 5−, and 7-carbon monosaccharides. Ribulose 5-phosphate is acted upon by an enzyme epimerase to produce xylulose 5-phosphate while ribose ketoisomerase converts ribulose 5-phosphate to ribose 5-phosphate. The enzyme transketolase catalyse the transfer of two carbon moiety from xylulose 5-phosphate to ribose 5-phosphate to give…

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:

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…

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

Skeletal muscle and brain use a different NADH shuttle, the glycerol 3-phosphate shuttle. It differs from the malate-aspartate shuttle in that it delivers the reducing equivalents from NADH to ubiquinone and thus into complex III, not complex I, providing only enough energy to synthesise 1.5 ATP molecules per pair of electrons. Summing up the reaction sequence:…