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Abstract: The formation of 18-molybdopyrophosphate anion has been studied to develop a simple and rapid assay of the enzymatic reaction involving . By the addition of anion to an acidic acetonitrile–water solution containing anion, the colorless Mo(VI) solution immediately became yellow due to the formation of 18-molybdopyrophosphate anion. The absorbance of the mixture at, for example, 450nm was proportional to the analytical concentration of anion. Although the test Mo(VI) solution remained colorless by the addition of AMP, it gradually turned to yellow by ATP. The undesired color development is attributed to the formation of a yellow molybdophosphate species accompanied by the dissociation of from the unstable ATP molecule. However, the color development became much slower when ethylenediaminetetraacetic acid was added into an assay mixture, where ATP may form a kinetically stable species. Thus, anion can be determined spectrophotometrically in the enzymatic reaction mixture containing ATP. By the addition of ascorbic acid, the yellow mixture turned to blue due to the reduction of the molybdopyrophosphate anion. Thus, anion can be detected colorimetrically by the blueness. The spectrophotometric and colorimetric methods could be applied advantageously to the assay of acetyl-CoA synthetase. [Copyright &y& Elsevier]

ϵ-Poly-L-lysine (ϵ-PL) exists as a cationic polymer in acidic solution. Yellow tetravalent 12-molybdosilicate ([SiMo12O40]4−) anion is formed in acidic solution containing and anions. By mixing the test ϵ-PL solution with the acidic − solution, the [SiMo12O40]4− anion associates with the cationic ϵ-PL to form yellow precipitate. The yellowness of the supernatant decreased with the initial concentration of ϵ-PL in the test solution due to the residual [SiMo12O40]4− anion. By addition of ascorbic acid to the supernatant, the residual [SiMo12O40]4− anion was reduced to blue molybdosilicate species. Thus the concentration of ϵ-PL in sample media can also be estimated by the blueness of the reaction mixture. The present method can be applied successfully to the screening of ϵ-PL-synthetase in culture media. [ABSTRACT FROM AUTHOR]

We describe a new colorimetric assay method using glucose oxidase (GOx) to detect ε-poly- l -lysine (εPL). This method uses εPL's remarkable effect of promoting the enzymatic reaction of GOx with ferricyanide ion. This reaction reduces ferricyanide ion to ferrocyanide ion, accompanied by a color change from yellow to colorless. In this colorimetric assay, the detection limit of εPL was estimated to be approximately 0.5 mg/L when purified εPL samples were used. εPL has usually been produced by a fermentation process using Streptomyces albulus species. The components of the culture broth showed interference effects against the assay method. However, due to the high sensitivity of the assay method for εPL, εPL could be detected in the culture broth without any pretreatment. The detectable concentration of εPL in the culture broth, c PL,ac , was estimated to be approximately 20 mg/L. By combining the Berlin blue reaction with this method, the c PL,ac was reduced to 10 mg/L. In light of the proposed method's simplicity and sensitivity, it could be useful for screening εPL synthetic enzymes and microorganisms. [ABSTRACT FROM AUTHOR]