Abstract
We describe the enzymatic determination of urinary methylguanidine with methylguanidine amidinohydrolase (EC 3.5. 3.16) and methylamine oxidase. In the first step, urinary methylguanidine was hydrolyzed by methylguanidine amidinohydrolase to methylamine and urea. Methylamine was subsequently oxidized by methylamine oxidase to formaldehyde and hydrogen peroxide. The formaldehyde reacting with methyl 3-aminocrotonate gave a fluorescence product. The fluorescence intensity was measured at an excitation wavelength of 375 nm and an emission wavelength of 465 nm. Good linearity was obtained in a wide range of methylguanidine concentrations (0.02-8.00 mg/l). The analytical recovery of methylguanidine added to urine ranged from 96.5 to 98%. The results obtained by the present method correlated well (r=0.984) with those obtained by the high-performance liquid chromatographic method. The proposed method is accurate and simple. The mean methylguanidine concentration in healthy spot urine samples was 560, μg/l. We determined the concentration of methylguanidine in 24-h urine samples by the above method, and found that the urinary excretion of methylguanidine increased markedly in samples of inpatients with chronic renal failure.
