Methylumbelliferyl-N-acetyl-neuraminic acid (MU-NANA) sialidase in human fibroblasts. Further characterization of the enzyme.

The enzyme properties of acid sialidase have been investigated in cultured fibroblasts. An extended period of homogenization at 0 degree C, did only minimally inactivate the enzyme and 90% and 80% of the activity was recovered after 3 and 5 minutes of homogenization respectively. Bovine serum albumin is an affective protector of the enzyme. The activity of the enzyme was 70% and 18% respectively at 23 degrees C and 0 degree C, in comparison with the activity measured at 37 degrees C. 55% of the sialidase activity was recovered after a homogenate had been kept frozen for 6 months at--20 degrees C. Methoxyphenyl-sialic acid, colominic acid, and sialyllactose are all competitive inhibitors. The Vmax value in fibroblasts of a patient with mucolipidosis II was about 40 times lower than in normal control fibroblasts.