Subject pentose phosphate pathway

The diagnosis of G6PD deficiency is made by quantitative or semiquantitative assay. The methods used are based on the normal function of the G6PD enzyme in catalyzing the initial step in the pentose phosphate pathway (PPP). Screening tests depend on the inability of cells from deficient subjects to convert an oxidized substrate to a reduced state. The substrates... 

Put at its most simple, the reactions of the pentose phosphate pathway can be considered as a series of shuffling steps in which units are exchanged between five- and six-unit structures. In this form the pathway lends itself readily to mathematical analysis, because we can ask whether the particular set of exchanges is the most efficient that can be conceived. This will be the subject of Chapter 5. 

Fig. 6. The effect of P5C on pentose phosphate pathway (HMP) activity and phosphoribosyl pyrophosphate (PPRP) in human erythrocytes. Measurements were performed on incubated erythrocytes from 6 normal subjects. The concentration of pyrroline-5-carbox-ylate (PC) was 0.5 mM. Taken from ref. (116).

Proof for the existence of a mechanism for the direct oxidation of pentose phosphate has not been provided as yet. However, it has been demonstrated that one pathway of pentose phosphate metabolism involves initially a cleavage to produce those phosphate and a 2-carbon unit, the nature of which is the subject of current investigation. 

By contrast with the reactions subject to metabolic regulation in the photosynthetic pathways of carbon, the conversion of G6P to 6-phosphogluconate by G6P dehydrogenase— the first enzyme of the oxidative pentose phosphate < cle—is inactivated in the light and activated in the dark. Light inactivation may be a reductive process since dithiothreitol treatment of crude extracts produces similar inactivation. ... 

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