Other Metabolically Important Organic Acids

This transamination reaction is a widespread process of importance in many aspects of the nitrogen metabolism of organisms. A large series of transaminases (aminotransferases), for which glutamate is most often one of the reactants, have been shown to catalyze the reactions of other oxoacids and amino acids.141-143... 

Availability is not the only constraint on substrate consumption. The value of a substrate is also related to the resources needed to convert the molecule into an intermediary metabolite. Thus in aerobic environments, monosaccharides and amino acids are readily consumed under anaerobic conditions, heterotrophic metabolism is largely fueled by small organic acids. Some taxa consume other types of substrates as long as they are reasonably abundant. Important examples include P-proteobacteria that consume phenols, a significant component of DOM inputs originating from plant material, and methylotrophs that consume single carbon compounds produced by anaerobic metabolism, photochemical reactions, and oxidation of methyl and methoxy substituents (Giovannoni and Rappe, 2000). 

Organic acids in dairy and other food products have commonly been analyzed by chromatographic techniques. An alternative RP-HPLC method has been optimized for analysis of multiple 11 organic acids that are metabolically of importance in dairy products (Tormo and Izco, 2004). 

Excretion. Although direct evidence exists for outward transport of inorganic ions across the cuticle of A. suum (127), little is known about the relative importance of the cuticle, intestine or putative excretory canal system in nematodes for outward transport of metabolic end-products or other organic molecules. Organic acid end-products of carbohydrate metabolism are excreted across the cuticle in A. suum (129) and H. contortus (123). This process generates a microclimate pH within the aqueous pores of the cuticle which is maintained at pH 5.0, near the pK of the excreted organic acids (130). 

On the other hand, organic acids are more difficult to measure in the labs. Usually, these are measured by GC or HPLC. However, CE offers speed, precision, and specificity over other methods. Organic acids are important in inborn errors of metabolism, in infection, and different metabolic disorders. Many of these compounds have been measured by CE directly, or by indirect UV absorbency after addition of a UV absorbing compound such as benzoate, naphthalene sulfonate, imidazole, or benzylamine. For example, oxalate and citrate, which are important in stone formation, have been measured after urine dilution by both direct and indirect detections. Lactate, pyruvate, ascorbate, and oxalate were measured by CE in the CSF of patients in 10 min. Methylmalonic acid, which is a sensitive measure of vitamin Bi2 deficiency preceding any clinical symptoms or changes in the serum, has been determined in m-ine by CE after sample extraction and concentration. 

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