The
enterotoxin of Vibrio cholerae causes copious fluid production throughout the lenght of the small intestine. As this is thought to be mediated by stimulation of
adenyl cyclase, a study has been made of the activity and properties of this
enzyme in jejunal biopsy tissue taken from patients during the diarrheal phase of
cholera and after recovery.
Adenyl cyclase activity during
cholera was increased more than twofold relative to the
enzyme in
convalescence. Under both conditions stimulation by
prostaglandin E(1) (
PGE(1)) and by
fluoride was observed. The responsiveness to
PGE(1) was not altered in
cholera; the total activity of the
fluoride-stimulated
enzyme was similar, a finding that suggests
cholera toxin stimulates pre-existing
enzyme in the intestinal cell. The
enzymes during
cholera and
convalescence were similar in all other properties examined. Optimal Mg(++) concentration was 10 mM; Mn(++) at 5 mM stimulated the
enzyme but could not replace Mg(++) except in the presence of 10 mM
fluoride.
Calcium was markedly inhibitory at concentrations greater than 10(-4) M. The pH optimum was 7.5 and the Michaelis constant (K(m)) for
ATP concentration approximated 10(-4) M. Thus the interaction of
cholera toxin with human intestinal
adenyl cyclase does not alter the basic properties of the
enzyme. When biopsy specimens were maintained intact in oxygenated
Ringer's solution at 0 degrees C, no loss of activity was observed at 1(1/2) and 3 hr. In contrast, when the cells were homogenized, rapid loss of activity, with a half-life of 90 min was seen even at 0 degrees C. Consequently for comparative assays of human jejunal
adenyl cyclase, strict control of the experimental conditions is required. It was under such conditions that a twofold increase in basal
adenyl cyclase activity during
cholera was observed.