Glucose reaction with alanine

Many dehydrogenase enzymes catalyze oxidation/reduction reactions with the aid of nicotinamide cofactors. The electrochemical oxidation of nicotinamide adeniiw dinucleotide, NADH, has been studied in depthThe direct oxidation of NADH has been used to determine concentration of ethanol i s-isv, i62) lactate 157,160,162,163) pyTuvate 1 ), glucose-6-phosphate lactate dehydrogenase 159,161) alanine The direct oxidation often entails such complications as electrode surface pretreatment, interferences due to electrode operation at very positive potentials, and electrode fouling due to adsorption. Subsequent reaction of the NADH with peroxidase allows quantitation via the well established Clark electrode. 

The teichoic acid which had not been subjected to ion-exchange chromatography contained D-alanine in characteristic, labile, ester linkage. It contained insufficient glucose to accommodate all of the alanine ester residues (alanine phosphorus ratio, 0.89 1), and the kinetics of the reaction with hydroxylamine indicated that all of the alanine is attached to the available hydroxyl groups at C-2 of glycerol residues. 

One of the first researchers to study the aroma formation during the Maillard reaction was Ruckdeschel [21] in 1914. He described the reaction product of glucose with phenylalanine as rose-like, with leucine as bread-like, with valine as fine roasted and with alanine as similar to coloured malt. 

Figure 4. Gas chromatogram of authentic sample and model system extracts. (A) maltol (B) extracts from the reaction of fructose and p-alanine (C) the extracts from the reaction of glucose and p-alanine. GC column 30 m x 0.25 mm (i.d.) fused silica capillary column bonded and cross-linked with DB-1 (film thickness 0.25 pm) temperature program, 50°C for 8 min, 50-250°C/min, isothermal hold at 250°C. Internal standard is dodecane.

It is not yet clear whether biotin is a cofactor no biotin was detected in highly purified preparations of the enzyme. Malate easily converts to oxaloacetate. The formation of oxaloacetate by one of these two pathways is significant, because it provides the initial spark for the citrate cycle, since oxaloacetate is needed as partner for the condensation reaction with acetyl-CoA. Furthermore, oxaloacetate mediates the resynthesis of glucose (see below). It should be pointed out, finally, that pyruvate can be transformed to alanine (Chapt. VIII-10) by transamination so that pyruvate also represents a link to the metabolism of protein. 

The ESR spectra of reaction mixtures of glucose with a- and 3-alanine differed from each other in the complexity of their hyperfine structure, the former being split into 19 lines and the latter into 25 lines. This difference was shown to depend on... 

Figure 1. Free radical formation and browning in the reaction of D-glucose with a-alanine or fi-alanine (each 3 MJ, and ESR spectra of the reaction mixtures heated...

Figure 7. Formation of free radical and other intermediates in the reaction of glucose with fi-alanine. The mixture (each 2 M) with aqueous alkali solution (0.1 N NaOH) was heated in a boiling water bath. Key , free radical O, browning A, 1-fl-alanino-l-deoxyfructose and , 3-deoxyglucosone. (Reproduced with...

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