Compartmentation of metabolic pathways

Compartmentation of individual metabolic pathways is an important element of metabolism regulation. The division of the cell into separate compartments allows opposing metabolic pathways to take place in the cell at the same time. It also simplifies the regulation of some lanes. For example, the regulation of β-oxidation is based on this principle, where the rate of fatty acid oxidation is dependent on the entry of fatty acids into the mitochondrion.

Transport of metabolites between compartments
Metabolites are substances that are often soluble in water and therefore cannot pass through the membrane on their own. This applies both to the cytoplasmic membrane and to the intracellular membranes delimiting individual compartments. Therefore, transport mechanisms are needed. Most metabolites have their carriers in the membranes – pyruvate, citrate, malate easily pass through the membrane. Considering that metabolites are often associated with large molecules, it would be useless to transport whole molecules and thus only their parts are transported.

Three transport systems are particularly important in metabolism:
 * carnitine transport system;
 * malate-aspartate and glycerol phosphate shuttle.

Compartmentation also complicates the onset of gluconeogenesis. The enzyme pyruvate dehydrogenase is only present in mitochondria. The resulting oxalacelate cannot pass through the membrane, so it must be transaminated to aspartate or reduced to malate, which pass through the membrane and are converted back in the cytosol.

Related articles

 * Regulation of metabolism at the cell level
 * Regulatory enzymes
 * Regulation of individual metabolic pathways