Demonstration of Neuraminidase Activity in Human Blood Serum and Human Milk Using a Modified, Radioactively Labelled α1-Glycoprotein as Substrate

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Abstract
N-Acetylneuraminic acid of .alpha.1-glycoprotein was oxidized with a small excess of periodate and reduced with 3H-borohydride. This converted about 50% of the N-acetylneuraminic acid to its radioactively labeled C8-analog and 25% to its C7-analog. Using this modified .alpha.1-glycoprotein as substrate, minimum neuraminidase concentrations of 10-18 units/ml, related to the activity of neuraminidase from Vibrio cholerae, could be determined. Neuraminidase activity was demonstrated in 95% of the sera or blood plasma samples from a series of 417 healthy or ill human individuals and in all milk samples from 5 donors. The neuraminidase in both serum and milk had optimal activity at pH 5.5. An average of 10-10 neuraminidase units were found in 1 ml serum and 10-8 units 1 ml milk. Although the neuraminidase activities in the sera varied, a correlation with definite pathological states is not yet possible. N-Acetylneuraminate pyruvate-lyase activity could not be detected in human serum.

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