Year: 1971
Type: article
Abstract: SOCIETY 95P75 000) are totally excluded from the mitochondrion, certain smaller molecules such as sucrose penetrate only as far as the inner membrane and the total water space may be measured with tritiated water.Using these spaces as markers, we have investigated the distribution volumes for (-)-carnitine and acetyl-(-)-carnitine in rat liver mitochondria in- cubated at 00C for 3min at pH7.2 in a medium consisting of tris-HCl buffer (20mM), potassium chloride (80mM), EDTA (1mM) and sucrose (20mM).After incubation mitochondria were obtained by centrifugation at 12000g for lOmin.In these experiments the total pellet water averaged 2.22 ,ul/mg of protein and the [14C]sucrose and [14C]dextran spaces were 68% and 38% respective- ly of the total pellet water.The penetration of tritiated (-)-carnitine was identical with that of sucrose.However, values for the acetyl-(-)carnitine space, measured enzymically, were quite erratic and occasionally less even than the dextran space.This anomaly was traced to a breakdown of acetyl-(-)-carnitine during the incubation and sub- sequent manipulations.Experiments were there- fore repeated, but the technique of high-speed centrifugation of mitochondria through a silicone layer into perchloric acid was employed to give a near-instantaneous deproteinization of the mitochondria after separation from the incubation medium.In this system the acetyl-(-)-carnitine space was also found to be identical with the sucrose space.In parallel experiments the addition of acetyl-(-)-carnitine was observed to elevate the intramitochondrial acetyl-CoA concentration from 0.88 to 1.4nmol/mg of protein.This suggests that acetyl groups enter the mitochondrial matrix under conditions in which acetyl-(-)-carnitine does not penetrate the inner membrane.Results reported suggest the concept of an anisotropic mechanism for carnitine facilitation of fatty acyl group translocation (Haddock, Yates & Garland, 1970), provided that two assumptions are valid.First, acetyl-(-)- carnitine must not have been rapidly removed as soon as it entered the matrix.Secondly, it is assumed that discrete subcompartments of the mitochondrial matrix do not exist.If there were compartmentation within mitochondria, small changes in accumulation of acetyl-(-)-carnitine might well be non-detectable.The validity of these assumptions will be discussed.
Source: Biochemical Journal
DOI: 10.1042/bj1250095p
Authors: D M F Cooper, W K Downey
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2416211349