By removing physical barriers and inhibiting protein production, Nijmegen researchers were able to experimentally demonstrate that macromolecular crowding does indeed play a role in mitochondria. But whether that role is positive or negative varies by situation and process.

Specific organelles in eukaryotic cells, mitochondria, produce ATP and thus act as the cell’s power plants. Mitochondria, like the rest of the cell, are packed with proteins. This causes macromolecular crowding in the cell; the phenomenon in which a high protein concentration reduces the diffusion rate of proteins and other (macro)molecules. ‘Macromolecular crowding affects all reactions in an indirect way, by changing the environment in which those reactions take place,’ says Werner Koopman, associate professor at Radboudumc in Nijmegen and specialized in mitochondrial diseases and bioenergetics.