Distribution of reaction intermediates on chicken liver fatty acid synthase.

Published

Journal Article

The distributions of covalent intermediates in the reaction cycle catalyzed by chicken liver fatty acid synthase were studied. In isotope-trapping experiments, 30% of [1-14C] acetyl-enzyme and 6.7% of [2-14C]malonyl-enzyme are converted to long-chain fatty acids, indicating the initiation reaction is partially random. The 3-hydroxybutyryl intermediate is located on the tryptic peptide which contains the 4'-phosphopantetheine (greater than 90%), while the C4-C18 saturated intermediates are distributed both on this peptide and on the peptide that contains the active cysteine. The ratio of intermediates on the two peptides is about unity for chain lengths less than C14, but the amount on the active cysteine progressively decreases for chain lengths of C14, C16, and C18 with trypsinized enzyme. The distributions of carbon chain lengths for the saturated or 3-keto intermediates when acetoacetyl-labeled trypsinized enzyme is incubated with limiting malonyl coenzyme A or NADPH, respectively, show large fractions both of unreacted enzyme and of C16 or longer intermediates. A detailed analysis suggests that the initial condensation and reduction steps are slower than the analogous reactions with longer chain length intermediates. The 3-keto intermediate comprises over 70% of each chain length intermediate detected when NADPH is the limiting substrate, indicating the reduction of the 3-keto intermediates is at least 2 times slower than the reduction of the unsaturated intermediates.

Full Text

Duke Authors

Cited Authors

  • Anderson, VE; Hammes, GG

Published Date

  • April 23, 1985

Published In

Volume / Issue

  • 24 / 9

Start / End Page

  • 2147 - 2154

PubMed ID

  • 3995008

Pubmed Central ID

  • 3995008

International Standard Serial Number (ISSN)

  • 0006-2960

Digital Object Identifier (DOI)

  • 10.1021/bi00330a007

Language

  • eng

Conference Location

  • United States