{'fraction_non_alphanumeric': 0.02967525195968645, 'fraction_numerical': 0.005599104143337066, 'mean_word_length': 5.016835016835016, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 2, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 1, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Structure-activity relationships of cardiotonic steroids for the inhibition of sodium- and potassium-dependent adenosine triphosphatase. IV. Dissociation rate constants for complexes of the enzyme with cardiac oligodigitoxides.

The dissociation rate constants (kd) of (Na+ + K+)-ATPase (EC 3.6.1.3) complexes with digitoxigenin or digoxigenin oligodigitoxides were determined by enzymatic assay after dilution. The kd value of each cardiac glycoside—enzyme complex formed in the Na+-Mg2+-ATP system (type I complex) was greater than that of the complex formed in the Mg2+-P[unknown] system (type II complex). In type I complexes the kd value of the digitoxigenin oligodigitoxide complex was greater than that of the digoxigenin oligodigitoxide complex, but this difference was diminished in the type II complex. For a given aglycone and type of complex, the kd values decreased in the order monodigitoxide > bisdigitoxide > tridigitoxide [unknown] tetradigitoxide. The activation energies of these dissociation constants were approximately 30 kcal/mole for the type I complex and 25 kcal/mole for the type II complex and did not change with the number of sugar moieties or the nature of the aglycone. The kd values of the type II complexes were increased with Na+ plus ATP in the dilution medium in a manner similar to those of the monoglycosides. On the other hand, K+ in the dilution medium reduced the kd values of only the type I complexes containing cardiac oligodigitoxides. These kd values fell below those of the type II complex, in contrast to the situation with the cardiac monoglycosides. These results suggest that the second and third digitoxose moieties of the cardiac digodigitoxides can bind to the enzyme but that binding by the first digitoxose moiety is predominant.