Pentos Phosphate pathway :
i. During respiration brakdown of glucose in cytosol occurs by glycolysi (about 2/3) as well as by oxidative pentose phosphate pathway (about 1/3) . Pentose phosphate pathway was described by Warburg, Dickens and Lipmann (1938).
ii. Hence, it is also called Warburg - Dickens- Lipmann pathway. It rakes place in cytoplasm of mature plant cells. It is an alternate way for breakdown of glucose.
It is also known as Hexose monophosphate shunt (HMP Shunt ) or Direct Oxidative Pathway. It consists of two phases, oxidative phase and non - oxidative phase.
iii. The oxidative enent convert six molecules of six carbon glucose - 6- phosphate to 6 molecules of five carbon sugar ribulose -5 phosphate with loss of `6CO_(2)` molecules and generation of 12 NADPH ` + H^(+)` ( not NADH).
iv. The remaining reactions known as non-oxidative pathway, convert Ribulose -5- phosphate molecules to various intermediates such as ribose -5- phosphate (5 C), xylulose 5-phosphate (5C), glyceraldehyde -3-phosphate (3C), sedoheptulose - 7- Phosphate (7C) , and erythrose -4- phosphate (4C).
v. Finally, five molecules of glucose -6- phosphate is regenerated . The overall reaction is :
`6 xx ` glucose -6- phosphate ` + 12 "NADP"^(+) + 6H_(2)O`
` 5 xx ` glucose -6- phosphate ` + 6CO_(2) + Pi + 12 " NADPH " + 12H^(+)`
The net result of complete oxidation of one glucose -6- phosphate yield `6CO_(2)` and 12 NADPH ` + H^(+) `. The oxidative pentose phosphate pathway is controlled by glucose -6- phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to `"NADP" + `.
