Surface enzymes in cultured fibroblasts from cystic fibrosis patients.

Membrane function was examined in cultured cells from cystic fibrosis patients by 
assaying several enzymes on intact skin fibroblasts attached to culture dishes. 
This technique required few cells and minimized disruption of cellular organization. 
Comparison of enzyme activities of intact and broken cells showed that 
12% of total glucose-6-phosphate dehydrogenase, a cytoplasmic enzyme, was measurable using 
intact cells, while all adenosine monophosphatase was measurable using intact cells. 
Alkaline paranitrophenylphosphatase activity was divided between the cell surface and interior. 
Substrate competition experiments indicated that substrate specificities for adenosine monophosphatase and 
paranitrophenylphosphatase activities were different. Adenosine monophosphatase activities of 2 control and 
2 cystic fibrosis strains fluctuated similarly during the cell culture cycle. 
The apparent Km values relative to adenosine monophosphate were similar in 
all strains. A chromatographic fraction of serum from a cystic fibrosis 
patient that was inhibitory to oyster ciliary activity had no effect 
on adenosine monophosphatase activity of normal fibroblasts. Furthermore, fractions of media 
from cystic fibrosis homozygote and heterozygote fibroblast cultures were not inhibitory 
to adenosine monophosphatase activities of intact normal fibroblasts or of part 
iculate fractions prepared from them. In light of previous studies that 
showed that factors from cystic fibrosis serum of culture medium disrupted 
specific membrane activities, it is proposed that the cystic fibrosis factor 
interacts with the plasma membrane, interfering most conspicuously with the protein 
functions that are sensitive to changes in their membrane environment. 