title: Mammalian acetoacetate decarboxylase activity. Its distribution in subfractions of human albumin and occurrence in various tissues of the rat.
abstract: In this article further information is presented about the characteristics of the mammalian enzyme acetoacetate decarboxylase (acetoacetate carboxylase, EC 4.1.1.4). The Michaelis-Menten plot shows a sigmoidal relationship between the enzyme activity (v) and the substrate concentration (s) indicating an allosteric hindrance. Because of this, the KM value can only be predicted to be equal to or less than 1 X 10(-1) M. Cysteine and glutathione, although activating the spontaneous decarboxylation, have no effect upon the enzyme activity. From experiments with human albumin by means of gel filtration with Sephadex G-200, it can be concluded that the acetoacetate decarboxylase activity does not depend upon the degree of polymerisation of albumin. From experiments performed by means of ion exchange chromatography the enzyme activity may be localized in the non-mercaptalbumin fraction. Investigation of enzyme activity in homogenates of various rat tissues, as well as in their respective subfractions, reveals that: (1) the specific activity of brain tissue exceeds those of liver and kidney and (2) most of the activity in liver tissue is localized in the 20 000 X g supernatant, containing the endoplasmatic reticulum, the ribosomes and the soluble part of the cytoplasm, while in brain tissue a high activity is found in the nuclei fraction.
mesh_terms: D000090:Acetoacetates / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology; D002262:Carboxy-Lyases / Q000378:metabolism*; D003545:Cysteine / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008970:Molecular Weight; D051381:Rats; D012709:Serum Albumin / Q000302:isolation & purification*; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D000090:Acetoacetates; D012709:Serum Albumin; D002262:Carboxy-Lyases; C023743:acetoacetate decarboxylase; D005978:Glutathione; D003545:Cysteine