Biomedical subjects

W Biermans

Publications and source records attributed to W Biermans.

4 recordsLinked to original sources

PubMed1994

Ultrastructural localisation of carnitine acetyltransferase activity in mitochondria of rat myocardium.

The acetyl CoA/CoA ratio is an important regulating factor of beta-oxidation in mitochondria and hence of energy production in the myocardium. Carnitine acetyltransferase provides one of the control mechanisms for this ratio during changing energy demand in the heart muscle, possibly by buffering the CoA and carnitine concentration for sustained beta-oxidation. In search for a possible correlation between the activity of this enzyme and ultrastructural changes in heart mitochondria, carnitine acetyltransferase was cytochemically localised in rat myocardium, brought into different metabolic states. In this work we confirm previous observations, namely the formation of contact sites between inner and outer mitochondrial membranes upon catecholaminergic stimulation of the myocardium. It is further shown that this contact site formation might be a prerequisite for carnitine acetyltransferase to demonstrate enzymatic activity and hence control of beta-oxidation in myocardial mitochondria.

Animals↗

PubMed1994

Mitochondrial matrix granules: their behavior during changing metabolic situations and their relationship to contact sites between inner and outer mitochondrial membranes.

Since their discovery in the early fifties mitochondrial granules have been the subject of many researches. Some twenty years ago two hypotheses on their function were introduced. Peachey thought that the granules were a sink of cations and that they would eventually regulate the concentrations of these ions. Alternatively, Barnard thought that the granules were precursors of the mitochondrial inner membrane. There are only a few data on organic constituents of the granules. Phospholipids (e.g., cardiolipin) glycoprotein or lipids, calcium precipitable lipoprotein, cytochrome c oxidase seem to be present in the granules. There has been much debate on whether calcium is present or not. Reports are mostly based on X-ray microanalysis, the result of which depends on preparation techniques. In heart muscle in stimulating situations the NMG (native matrix granules) move towards the inner membrane and are incorporated in it. They appear to create contact sites between inner and outer mitochondrial membranes in which enzymes can function efficiently. It is hypothetized that the system, NMG-contact sites, forms the structural basis of a regulatory mechanism, by which cells can cope with a high and sudden energy demand.

Animals↗

PubMed1990

Contact site between inner and outer mitochondrial membrane: a dynamic microcompartment for creatine kinase activity.

Creatine kinase is involved in the integration of high-energy metabolism in various tissues. In this study the tissue-specific distribution of the mitochondrial isoform was investigated, both by electrophoresis of rat tissue extracts, and by ultrastructural localisation of creatine kinase activity. Furthermore, the influence of uncoupling of oxidative phosphorylation on mitochondrial creatine kinase activity associated with intermembrane contacts was investigated by enzyme cytochemistry and morphometric analysis. The results of the cytochemical survey indicate that contact sites are a prerequisite for creatine kinase to demonstrate enzymatic activity. Moreover, the extent of creatine kinase active membrane contacts depends on the metabolic state of the mitochondrion, as shown for heart mitochondria in vivo and in vitro, before and after treatment with dinitrophenol.

Animals↗

PubMed1989

Ultrastructural localisation of creatine kinase activity in the contact sites between inner and outer mitochondrial membranes of rat myocardium.

The mitochondrial isoenzyme of creatine kinase, together with the ADP/ATP translocase, most probably belongs to a functional multi-enzyme complex located on the inner mitochondrial membrane. The outer membrane is a necessary constituent of this microcompartment. On the other hand, electron microscopic visualisation demonstrated the formation of contact sites between inner and outer mitochondrial membranes as a reaction to variations of the energy metabolism. In search for a possible correlation between these biochemical and morphological phenomena, rat myocardia were brought into the required energy state by stimulation through catecholaminergic mechanisms or adjusted perfusion with amytal. Subsequently, creatine kinase was cytochemically localised. Creatine kinase activity is demonstrated in membrane contacts between inner and outer mitochondrial membranes. The extent of contact sites and creatine kinase activity depends on the metabolic state as shown by morphometric analysis of the surface density of cytochemical reaction product. This surface density diminishes drastically after inhibiting the metabolic activity with amytal. It is concluded that these contact sites are dynamic micro-environments in which the active site of creatine kinase, oxidative phosphorylation and ADP/ATP transport interact during basal and stimulated metabolism.

Amobarbital↗