This review describes in vivo NMR measurements of metabolite diffusion. NMR spectroscopy can employ a variety of endogenous marker molecules to obtain information on various aspects of in vivo biochemistry and biophysics from the diffusion characteristics of these markers. NMR-based metabolite diffusion data give an insight into the physico-chemical properties of the intracellular compartment and of changes therein in relation to development and pathology. Recent applications have proven that in vivo diffusion spectroscopy provides exciting opportunities to both fundamental and applied research.

Animals↗

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The influence of the cytosolic oncotic pressure on the permeability of the mitochondrial outer membrane for ADP: implications for the kinetic properties of mitochondrial creatine kinase and for ADP channelling into the intermembrane space.

Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed.

Adenosine Diphosphate↗