Carboxypeptidase B activity of cultured skin fibroblasts and relationship to cystic fibrosis.

Enzyme activity against hippuryl-L-arginine was studied in cultured skin fibroblasts from controls 
and cystic fibrosis patients. The enzyme had a lysosomal distribution and 
an acid optimum of pH 4.5 with little or no activity 
present above pH 7.0. Dithiothreitol was required for full activity and 
the kinetics of thiol activation were different for the control and 
cystic fibrosis enzyme. The properties and lysosomal distribution of the enzyme 
indicated that it was a carboxypeptidase B. Substrate affinity, thermolability, pH 
stability, the fall and rise in activity with subculture, the cyclical 
pattern of activity through serial passage and the level of activity 
were similar for the control and cystic fibrosis enzyme. 