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SynopsisThe enzyme peroxidase, a substrate (hydrogen donor), and hydrogen peroxide aggregated and polymerized soluble proteins included in the reaction mixture. Gel filtration and acrylamide disk gel electrophoresis revealed newly formed dimers, trimers, and higher protein polymers. Some of the protein polymers withstood the denaturing conditions of dodecyl sulfate disk gel electrophoresis; thus the formation of some covalent cross links was indicated. It is suggested that peroxidase catalyzes the oxidation of hydrogen donors to form free radicals or quinones, which subsequently interact with, cross link, and alter the soluble proteins.

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The acyl-carrier protein (ACP) of Escherichia coli is a protein of molecular weight 8847 with a 4'-phosphopanthetheine prosthetic group. ACP functions (via the SH of the prosthetic group) as a coenzyme in the synthesis of fatty acids and complex lipids. We report proton nuclear magnetic resonance (NMR) studies of the structure of ACP under various experimental conditions. The motion of the fatty acyl chain of acyl-ACP has been investigated by 19FNMR studies of difluorotetradecanoyl-ACP. 31PNMR studies of the prosthetic group phosphorus of ACP and acyl-ACP are also reported. We make the following conclusions: (1) the structure of ACP is stabilized by surface charge, and (2) the fatty acid residue of acyl-ACP does not move freely and seems immobilized by an interaction with the protein moiety.