Abstract
A method to assay the level of neuraminidase in human plasma was developed. The synthetic fluorescent substrate N-acetyl-neuraminic-α-methylumbelliferil ketoside developed by Dr. M. Flashner of Syracuse, New York was used. Twenty μl of plasma and 200 μl of 60 μ mol of substrate in sodium hosphate buffer (pH 5.8) were mixed and incubated at 37°C for two hours. The rcaction was stopped by using 2, 500 μl of 10% sodium carbonate. The level of neuraminidase activiy was determined by measuring the fluorescence of methylumbelliferone which had been liberated by the activity of neuraminidase on the substrate. A fluorescent spectrophotometer (JASCO FP 550) using a wave length of 327 nm for excitation and an emission of 448 nm was used. Using this assay, Km was found to be 20μ mol 1 and the minimum measurable level of neuraminidase activity was 10-5U/ml. The assay was not influenced by protein in the plasma. This assay makes possible the measuring of a small amount of neuraminidase activity in the plasma.
