β-Oxidation as channeled reaction linked to citric acid cycle: Evidence from measurements of mitochondrial pyruvate oxidation during fatty acid degradation

Abstract

1. 1. The kinetics of mitochondrial mammalian pyruvate dehydrogenase multienzyme complex (PDHC) is studied by the formation of CO 2 using tracer amounts of [1- 14C]pyruvate. It is found that the Hill plot results in a (pseudo-)cooperativity with a transition of n−1→ 3 at a pyruvate concentration about K s . 2. 2. Addition of l-carnitine, octanoate, palmitoyl-CoA or palmitate + l-carnitine + fatty acid-binding protein results in a Hill coefficient of n = 2 following the kinetics of pyruvate oxidation. 3. 3. Addition of fatty acid-binding protein to an assay system oxidizing palmitate in presence of l-carnitine alters the pattern of the kinetics in the Hill plot so that an apparently lower level of l-carnitine is necessary for the reaction course of β-degradation. 4. 4. It is concluded that β-degradation is a coordinated, multienzyme-complex based mechanism tightly linked to citric acid cycle and it is proposed that l-carnitine is actively involved into the reaction and not only functioning as carrier-molecule for transmembrane transport.