Delta 3,5, Delta 2,4-dienoyl-CoA isomerase in the beta oxidation of unsaturated fatty acids: Characterization and metabolic significance.
Item
-
Title
-
Delta 3,5, Delta 2,4-dienoyl-CoA isomerase in the beta oxidation of unsaturated fatty acids: Characterization and metabolic significance.
-
Identifier
-
AAI9959230
-
identifier
-
9959230
-
Creator
-
Shoukry, Khaled.
-
Contributor
-
Adviser: Horst Schulz
-
Date
-
2000
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Chemistry, Biochemistry
-
Abstract
-
The degradation of unsaturated fatty acids by beta-oxidation involves three auxiliary enzymes in addition to the enzymes required for the breakdown of saturated fatty acids. These auxiliary enzymes, 2,4-dienoyl-CoA reductase and Delta3,Delta2-dienoyl-CoA isomerase and Delta3,5,Delta2,4-dienoyl-CoA isomerase (dienoyl-CoA isomerase), are necessary for the metabolism of preexisting double bonds.;The recently detected mitochondrial dienoyl-CoA isomerase was purified 370-fold from rat liver at almost 30% yield by a six-step purification procedure. The molecular weights of the native enzyme and its subunit were estimated to be 126,000 and 32,000, respectively. The purification of dienoyl-CoA isomerase completes the characterization of the enzymes functioning in the reductase-dependent pathway for the beta-oxidation of unsaturated fatty acids with odd-numbered double bonds. This novel pathway is operative in peroxisomes as indicated by the subcellular localization of dienoyl-CoA isomerase in mitochondria and peroxisomes. The peroxisomal and the mitochondrial forms of the isomerase exhibit similar substrate specificities.;The metabolic significance of the reductase-dependent pathway was assessed with 2-trans-5-cis-octadienoyl-CoA (2,5-octadienoyl-CoA) and its products, all of which are metabolites of alpha-linolenic acid. A kinetic evaluation of alpha-oxidation enzymes revealed that the presence of a 5- cis double bond in the substrate most adversely affected the activity of 3-ketoacyl-CoA thiolase although not enough to become rate-limiting.;Concentration-dependent and time-dependent measurements indicated that most (80%) of 2,5-octadienoyl-CoA is metabolized via the isomerase-dependent pathway. The reason for the greater flux through the isomerase-dependent pathway is the higher activity of L-3-hydroxyacyl-CoA dehydrogenase as compared with Delta 3,Delta2-enoyl-CoA isomerase. These two enzymes catalyze the rate-limiting steps in the isomerase-dependent and reductase-dependent pathways, respectively. Once 2,5-octadienoyl-CoA is converted to 3,5-octadienoyl-CoA (perhaps fortuitously because of the presence of Delta3,Delta 2-enoyl-CoA isomerase), the only effective route for its degradation is via the reductase-dependent pathway. It is concluded that the reductase-dependent pathway assures the degradation of 3,5-dienoyl-CoA intermediates, thereby preventing the depletion of free coenzyme A and a likely impairment of mitochondrial oxidative function.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
