Enzyme sarcosine dehydrogenase

Results forthcoming from the literature do not always assist in building a picture of events. The observation [65] that 2- and 4-hydroxylation of biphenyl was competitively inhibited by polysorbate 80 in the hamster contrasts with the finding that in the rat, polysorbate 80 (2mM) had no effect on the linear microsomal demethylation of aminopyrine (also a Type V substrate) [66]. The question arises whether surfactants such as polysorbate 80 produce their effects by interaction as an alternative substrate or by perturbation of a membrane bound enzyme system. Commercial samples of polysorbate 80, Brij 35 and Triton X-100 all enhance the activity of a sarcosine dehydrogenase isolated from a strain of Pseudomonas, due to the presence of free oleic acid in these non-ionic surfactants. Deoxycholate and a sarcosine surfactant (N-dodecanoyl N-methyl glycine) inhibit activity [67]. Correlations between the CMC of the non-ionic surfactants and the concentrations required for enzyme activation are seen in Table 10.9. 

The preferred absorption-based methods are those based on enzyme-catalyzed reactions. The absorbance of NADH (340 nm) after addition of creatine amidinohydrolase, sarcosine oxidase, formaldehyde dehydrogenase, and NAD to a creatine-containing solution is proportional to the concentration of creatine present. Creatinine amidohydrolase produces creatine from creatinine. Thus, any assays for creatinine which use creatinine amidohydrolase in the first step can be used for creatine by just leaving out that first step. Conversely, creatine can interfere in those analyses, although creatine is normally present in substantially lower concentrations than creatinine. 

Dimethylglycine is formed by endogenous demethylation of betaine, a choline metabolite, with concomitant methylation of homocysteine to methionine. DMG is then converted to sarcosine by oxidative demethylation catalyzed by DMG-dehydrogenase, a flavin-containing enzyme requiring folate as a cofactor. Increased excretion of DMG has been observed in individuals with folate deficiency or receiving large doses of betaine as a... 

Most studies have focused on amperometric glucose sensors based on GOx or GOx/ peroxidase [168-182]. However, a wide variety of other enzymes, including peroxidase, tyrosinase, choline oxidase, sarcosine oxidase, cholesterol oxidase, xanthine oxidase, glutamate oxidase, glutamate dehydrogenase, nitrate reductase, cholinesterase, cholesterol esterase, uricase, urease, creatinase, and creatininase, have also been employed for bioelectrosensor construction [183-203]. Representative examples are outlined in Table 2. 

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