Intracellular and extracellular alpha-D-mannosidase activity of cultured skin fibroblasts: relationship to cystic fibrosis.

Fibroblast intracellular alpha-D-mannosidase was inactivated by 30--50% after 120 min at 50 degrees C. Separation of alpha-D-mannosidase by isoelectrofocusing and wheat germ lectin-Sepharose into neutral and acid components showed the former to be heat labile and the cause of the observed loss. Fetal calf serum acid alpha-D-mannosidase could be inactivated at 60 degrees C if kept at pH 9.0. Fibroblast extracellular alpha-D-mannosidase was inactivated by 50--70% after 120 min at 50 degrees C, reflecting the greater level of the neutral component. Control and cystic fibrosis alpha-D-mannosidase showed no difference.