Neuraminidase activity in cultured fibroblasts from patients either with various forms of
sialidosis or with
I-cell disease (ICD) or
mucolipidosis (ML) III has been determined by both a colorimetric and a fluorometric method. The former applied to frozen fibroblast pellets demonstrated a specific deficiency of
neuraminidase in patients with the
sialidoses. The
enzyme was also deficient in I-cells, as were other lysosomal
hydrolases. With the
fluorogenic substrate these data could be confirmed and extended, and elementary kinetics of
neuraminidase studied. In unfrozen freshly harvested fibroblasts,
neuraminidase activity was severalfold that in frozen aliquots. A comparative and simultaneous study could not reveal substantial differences between the residual
neuraminidase activity found in the various clinical forms of
sialidosis. And, in fibroblasts from patients with ICD, also called
ML II, the deficiency of this
enzyme is quantitatively similar to that in the
sialidoses, but the residual activity in ML III is three times higher. In both
ML II and ML III the defect is probably secondary to the unknown metabolic error.