Cystic fibrosis: Enzymatic detection of a ciliostatic factor

The ciliostatic cystic fibrosis (CF) factor was investigated in order to develop an enzymatic assay for its detection. In saliva, this factor is associated with α amylase. Removal or addition of the factor by dialysis does not affect the α amylase catalytic activity of CF or control (normal) saliva. Crude preparations of the dialyzable factor from CF saliva are ciliostatic. α-Amylase-catalyzed starch hydrolysis from both CF and control saliva was found to be insensitive to hydroxyalkylamine inhibitors so this method could not be used to detect differences in CF and control amylase. Since another carbohydrase, mammalian debranching enzyme, is much more sensitive to inhibition, the effect of the isolated crude factor on this enzyme was determined. The mean values for percentage of inhibition of debranching enzyme activity by fractions obtained from saliva of CF patients, obligate heterozygotes, and control subjects are: 32% (27 samples), 13% (21 samples), and 6% (11 samples), respectively. Fifteen of the CF values exceed the maximum 13% inhibition observed for controls. Indeed, 5 samples almost completely inhibited debranching enzyme. This inhibitory action provides the basis of an enzymatic assay for the detection of the ciliostatic CF factor. These studies indicate that material isolated from CF saliva which contains ciliostatic activity also inhibits mammalian debranching enzyme. This action of the factor provides an enzymatic assay for its detection to replace the current bioassays. Although the assay is a useful method of detection for research purposes, lack of chemical quantitation of the factor at present precludes its use as a means of conclusively differentiating CF, carrier, or normal individuals.