title: Studies on the sialidoses: properties of human leucocyte neuraminidases.
abstract: At least two components of neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) can be distinguished in human leucocytes on the basis of pH optimum, thermolability at 30 degrees C and the effect of the detergent octyl-beta-D-glucoside. With 4-methylumbelliferyl-alpha-D-N-acetylneuraminate as substrate, the A component has a pH optimum of 5.0, is labile at 30 degrees C and is unaffected by 0.2 M octyl-beta-glucoside. The B component has a pH optimum of 4.0-4.2, is stable at 30 degrees C but loses most of its activity in the presence of 0.2 M octyl-beta-glucoside. Both A and B components are membrane-bound but only the A component is solubilized by octyl-beta-glucoside in an active form. Molecular weights of neuraminidases by gamma-ray radiation inactivation (a method that does not require solubilization of the enzyme) were found to be 240 000 +/- 19 000 for the B component, 203 000 +/- 17 000 for the A component and 238 000 +/- 8000 for the octyl-beta-glucoside-solubilized A component. Gel filtration of soluble A component on Sephacryl S-300, in the presence of octyl-beta-glucoside, showed a single peak of activity eluted at or near the void volume suggesting that the enzyme is still in an aggregated form. Profound deficiency of neuraminidase activity was found for both A and B components in leucocytes of patients affected with sialidoses type 1 and 2 (less than 15% normal) and intermediate activity in obligate heterozygotes. These results suggest that the A and B components of leucocyte neuraminidase are closely related from the genetic point of view and that rapid diagnosis of sialidoses can be done by fluorimetric assay of neuraminidase in leucocytes.
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005838:Genotype; D005960:Glucosides / Q000494:pharmacology; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007962:Leukocytes / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D009439:Neuraminidase / Q000097:blood / Q000172:deficiency* / Q000235:genetics; D012995:Solubility
chemical_list: D005960:Glucosides; C018619:octyl-beta-D-glucoside; D009439:Neuraminidase