The Journal of biological chemistry
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Acetoacetyl-CoA thiolase and 3-hydroxy-3-methylglutaryl coenzyme synthase which comprise the 3-hydroxy-3-methylglutaryl-CoA-generating system(s) for hepatic cholesterogenesis and ketogenesis exhibit dual mitochondrial and cytoplasmic localization. Twenty to forty per cent of the thiolase and synthase of avian and rat liver are localized in the cytoplasmic compartment, the remainder residing in the mitochondria. In contrast, 3-hydroxy-3 methylglutaryl-CoA lyase, an enzyme unique to the "3-hydroxy-3-methylglutaryl-CoA cycle" of ketogenesis, appears to be localized in the mitochondrion. ⋯ Chem. 248, 2275). Substantial mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase activity is present in all tissues surveyed, while only liver and kidney possess significant mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase activity. Therefore, it is proposed that tissues other than liver and kidney are unable to generate acetoacetate because they lack the mitochondrial synthase.
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Concanavalin A is a lectin composed of identical subunits, each containg 237 amino acid residues. The complete amino acid sequence of the first 129 residues of the polypeptide chain has been determined by analysis of peptides obtained from digests of CNBr Fragments F1 (residues 1 to 42) and F2 (residues 40 to 129). Correlation of the chemical sequence with x-ray crystallographic results indicates that Fragment F1 contains all of the protein ligands for the binding of 2 metal ions, Mn2+ and Ca2+, and that Fragment F2 contains many of the residues involved in the interactions of the subunits to form dimers and tetramers. The site of cleavage of the polypeptide chain to yield the naturally occurring Fragments A1 and A2 has also been identified as the peptide bond between residues 118 and 119.