Some bacterial species can metabolise pentose sugars which they obtain from hemicellulose breakdown. They incorporate pentose sugars into the Embden-Meyerhof pathway of glycolysis via the shunt mechanism known as the Pentose Phosphate Pathway. These species also oxidise some glucose by this route which uses NADP as the oxidising agent. This means they have to direct a proportion of the products of glycolysis toward NADP regeneration.

We shall see that the mechanisms used to achieve this result in Butyrate production.

The following three diagrams show how the Pentose Phosphate Pathway can channel metabolites toward glycolytic ATP production:

You should not rote learn these pathways. They are included here to remind you of the way five carbon sugars are produced from glucose and how their structures can be modified so as to be able to be funnelled into the ATP generating Emden-Meyerhof pathway whose end product is pyruvate. The further fate of pyruvate includes mechanisms to regenerate NADP.

1. the overall pathway showing the breakdown of cellulose and hemicellulose polymers to pyruvate.

The oxidation reactions identified by the * symbol use NADP as the oxidising agent.

2. the breakdown of the polymers to the intermediate substrates; xylulose 5 phosphate, ribulose 5 phosphate and ribose 5 phosphate

3. the breakdown of these intermediates to pyruvate yielding ATP using the enzymes: transketolase and transaldolase.

The patterns of carbohydrate fermentation looked at previously, when we examined metabolism in Veillonella, Selenomonas and Fibrobacter, were those that provide lactate, propionateand acetate.

We shall now examine fermentation patterns that produce butyrate, where NADP+ regeneration is one of the important outcomes.