Acid β‐mannosidase of human plasma: Influence of age and sex on enzyme activity

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Abstract
Optimum conditions for assay of human plasma β-mannosidase activity were determined. Maximum activity was observed at pH 3.0–3.4, the apparentK m was 0.9 mmol L−1 and enzymatic hydrolysis was linear for at least 60 min. Assays were performed on plasma from two siblings with the recently described condition β-mannosidosis and their parents and controls. Both β-mannosidosis patients showed a marked deficiency of β-mannosidase activity. Control samples showed no variation between sexes (p>0.05) but enzyme activity varied significantly with age (p<0.05). Highest activity was observed in the 0–1 year age group, activity then decreasing to adulthood, Both mother and father of the affected individuals showed reduced activity (34% and 53%, respectively) compared to age-matched controls. This suggests that heterozygote detection in this condition is possible using plasma, provided the variation of activity with age is taken into consideration.

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