HEXOSE MGNOPHOSPHATE SHUNT, SHUNT This pathway also called, 'pentose phosphate pathway'

already been discussed. HEXOSE MGNOPHOSPHATE SHUNT, SHUNT This pathway also called, 'pentose phosphate pathway' (PPP) is an alternative path of EMP. The main features are 1. This cycle operates, mainly in adipose tissue, lactat-ing mammary gland and to some extent in the liver Major steps are outlined below In the firsi stage glucose, becomes g1 6 phos as in the case of EMP But subsequently, the g16 phos is oxidized and decarboxylated resulting in formation of ribulose 5 phosphate (ribulose is a pentose) In the second phase, ribulose 5 phos becomes glucose again. There are numerous inermediats steps in both the stages , A and B, which need not be discussed. However, in the beginning, if there were. 6 molecules of glucose, at the end of stags B, only 5 molecules of glucose are resynthesized back, because one molecule of glucose molecule has been oxidized in the meantime By repeated recycling of glucose thro ughthe HMP cycle, oxidation of large amount of glucose is thus possible it should be noted that at no step of EMP, there is evolution of CO2, where at in the HMP, C02 evolution occurs early. The H released during the operation of PPP are accepted by NADP+(and not NAD+as in EMP), so that NADP+ becomes NADPH. Importance of PPP (i) Synthesis of fatty acids in the adipose tissue (from products of carbohydrate metabolism) requires large number of H atoms which can only be supplied by NADPH Thus fatty acid synthesis requires vigoros operation of PPP. Teleologically its occurrence in adipose tissue is ideal Another major utility of the shunt pathway i.e. the PPP appears to be, to produce pentoses for synthesis of nucleic acids and nucleotide Besides, PPP also yields energy. The interrelationship between PPP and fragility of RBC. especially after ingestion of the antirmalanal drug primaquine, has been discussed earlier in this book URONIC ACID PATHWAY In this pathway glucose is converted into uridine diphosphoglucuronic acid (UDP gfucuronic acid), via several steps including the conjugation with UTP (a high energy phosphate compound like ATP) and oxidation of ON radical attached wdh C6 of the glucose molecule. The glucuronic acid thus formed is utilized by The body as follows It combines with substances like estrogen, bilirubin and many drugs, forming the corresponding glucuronides (e. g . bilirubin gluucuronride) which are water soluble and excreted through urine (ii) in many mammals (but not in man and other primates or guinea pig) vit C can be synthesized Synthesis of vit C in those animals occurs from glucuronic acid SUMMARY & HIGH LIGHTS Glucose molecule is catabolized in many tissues (notably in the brain,