Abstract
To elucidate the molecular basis of cystic fibrosis (CF), we proposed the following working hypothesis: 1) the CF mutation resides in the structural gene encoding a specific proteolytic enzyme, 2) a function of which is to catabolize one or more small biologically-active peptides. 3) Reduction of this enzyme activity as a consequence of mutational alteration results in accumulation of its peptide substrate(s) whose cholinergic-like target specific action results in pathophysiological changes of CF. The results we report support the first contention and confirm the observations of Rao and Nadler. Plasma samples from 44 individuals: 10 cystics, 10 obligate heterozygotes, 12 age-matched normal individuals and 12 contrast patients (e.g. asthmatics, α1-antitrypsin deficients) were extracted with chloroform, activated with 1×10−4 ellagic acid and assayed for protease activity at 37° using nitrophenylated protamine sulfate (5 mg/ml) in 0.1M phosphate buffer pH 7.6 with 0.15M NaCl. Cleavage products were quantitatively determined with fluorescamine. All but two cystics had substantially reduced plasma protease levels (mean value 2.1±.3meq arg/ml plasma/hr) compared to heterozygotes (4.8±0.5), normal individuals (5.8±.5) and contrast subjects (5.1±0.5). The exceptions had borderline normal activities. Isoelectric focusing of normal plasma revealed five discrete protease species with pIs between pH 4 and 6. In the CF plasmas, the same protease species is decreased by ≥ 70%; activity lost from this fraction corresponds to the observed decrease in total protease activity of unfractionated CF plasma.
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Seale, T., Rennert, O. REDUCED PLASMA PROTEASE ACTIVITY IN PATIENTS WITH CYSTIC FIBROSIS. Pediatr Res 11, 463 (1977). https://doi.org/10.1203/00006450-197704000-00562
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DOI: https://doi.org/10.1203/00006450-197704000-00562