Fundamentals of Microbiology

3.1.4 Pentose phosphate pathway

The pentose phosphate pathway (or hexose monophosphate shunt) operates simultaneously with glycolysis. This is a cyclic pathway that provides a means for the breakdown of five carbon sugars (pentoses) as well as glucose.

A key feature of this pathway is that it produces in the synthesis of (1) nucleic acids, (2) glucose from carbon dioxide in photosynthesis, and (3) certain amino acids. The pathway is an important producer of the reduced coenzyme NADPH from NADP. Like NAD⁺, NADP carries an electron and a hydrogen atom. Twelve molecules of NADPH can be produced from each molecule of glucose if the glucose is completely oxidized. NADPH is then used in various biosynthetic reactions in the cell. Unlike glycolysis, the pentose phosphate pathway yields a net gain of only one molecule of ATP for each molecule of glucose oxidized. Bacteria that use the pentose phosphate pathway include Bacillus subtilis, E. coli, Leuconostoc mesenteroides and Enterococcus faecalis.

Entner doudoroff pathway

From each molecule of glucose, the Entner-Doudoroff pathway produces two molecules of NADPH and one molecule of ATP for use in cellular biosynthetic reactions.

The Entner - Doudoroff pathway is found in some Gram-negative bacteria, including Rhizobium, Pseudomonas, and Agrobacterium, it is generally not found among Gram-positive bacteria.