Competitive Inhibition of Human Brain Hexokinase by Metrizamide and Related Compounds

Abstract: We have compared the competitive inhibitory effects of 2-deoxyglucose, glucosamine, N -acetylglucosamine, N -benzoylglucosamine, and the commonly used radiographic and density gradient agent metrizamide (2-[3 - acetamido - 2,4,6 - triiodo -5-( N - methylacetamido) benzamido]-2-deoxyglucose) on the mitochondrial and soluble forms of human brain hexokinase. Metrizamide produces a classical competitive inhibition with glucose for human brain hexokinase, with K _is of 2.8 and 2.5 m M , respectively, for the mitochondrial and soluble forms. Glucosamine exhibited K _is of 0.58 and 0.29 m M , while 2-deoxyglucose exhibited K _is of 0.074 and 0.15 m M and N -acetylglucosamine 0.098 and 0.092 m M for these two forms, respectively. N -Benzoylglucosamine was by far the most effective inhibitor tested, with K _i values of 0.0086 and 0.022 m M , respectively. In order of increasing potency as a competitive inhibitor for mitochondrial hexokinase are metrizamide, glucosamine, N -acetylglucosamine, 2-deoxyglucose, and N -benzoylglucosamine. For the soluble form of the enzyme in increasing potency are metrizamide, glucosamine, 2-deoxyglucose, N -acetylglucosamine, and N -benzoylglucosamine. Since N -benzoylglucosamine was over 100 times more potent than metrizamide, some of the effects of metrizamide could be due to contamination by N -benzoylglucosamine. However, gas chromatography-mass spectrometry analysis of metrizamide did not indicate the presence of N -benzoylglucosamine. In addition, column chromatographic separation of commercially available metrizamide and reconstitution of freeze-dried eluate fractions localized the inhibitory effect to the metrizamide peak.