Sarcosine oxidase: structure, function, and the application to creatinine determination.

Determination of creatinine is important in the clinical laboratory. Jaffé reaction has long been used to determine creatinine, but the method suffers from various interferences. To overcome this problem, the enzymatic methods were invented and have been used widely. Sarcosine oxidase has a critical role in the enzymatic method. Of sarcosine oxidases,Corynebacterium enzyme has been studied extensively in kinetic and structural aspects. The enzyme contains noncovalently bound and covalently bound FADs, and consists of 4 non-identical subunits (A, B, C, D). The covalently bound FAD is bound to the subunit B. The rate of oxidation of sarcosine was explained by the rates of the oxidation and reduction of the bound FADs. From the chemical modification of the enzyme with iodoacetamide, the amino acid sequence around the non-covalently bound FAD is suggested and the modification changed the enzyme so that the only noncovalently bound FAD functions in the oxidation of sarcosine.