{'fraction_non_alphanumeric': 0.0374384236453202, 'fraction_numerical': 0.01625615763546798, 'mean_word_length': 4.72112676056338, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Metal-nucleotide structure at the active sites of the mammalian hexokinases.

The diastereomers of adenosine 5'-O-(2-thiotriphosphate) (ATP beta S) in the presence of Mg2+, Co2+ and Cd2+ have been used to determine the stereospecificity of the metal-nucleotide binding site of rat muscle hexokinase type II and rat liver glucokinase by the method developed by Jaffe and Cohn [J. Biol. Chem. 254, 10839-10845 (1979)]. The kinetic parameters, Km and V, for the mammalian hexokinase reaction have been determined for ATP beta S in the presence of the three divalent metal ions. In the presence of Mg2+, both enzymes exhibit a preference for the B diastereomer of ATP beta S (V ratio, B/A approximately equal to 20). With Cd+, the stereospecificity is reversed and the A diastereomer is the preferred substrate, suggesting direct coordination of S on the beta-P to this metal ion. Co2+ exhibits a decreased specificity for the B diastereomer over Mg2+. This decreasing order of stereo-specificity for the B isomer reflects primarily the decreasing ratios of nucleotide complexes coordinated to O rather than S on the beta-P as the metal ion is changed from Mg2+ to Co2+ to Cd2+. The kinetic parameters for the hexokinases have also been determined for adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) using the same three metal ions as activators. The A diastereomer is the preferred substrate regardless of the metal ion. This absence of reversal of stereospecificity for metal-ATP alpha S suggests that the alpha-P is not involved in coordinating the metal on the enzyme, unlike the beta-P. That is, the structural constraints of the ATP-binding site on the enzyme overcome the preferred coordination of Cd2+ to S. Given the greater stability of bidentate metal-ATP complexes over monodentate, these data are interpreted as indicating that MgATP binds to the mammalian hexokinases as the beta gamma-bidentate complex in the A screw sense geometry, as has been found for the yeast hexokinase (Jaffe and Cohn, reference cited above).