The proline cycle as an eukaryotic redox valve

The amino acid praline has been known for many years to be a component of proteins as well as an osmolyte. Many recent studies have demonstrated that proline has other roles such as regulating redox balance and energy status. In animals and plants, the well-described proline cycle is concomitantly responsible for the preferential accumulation of proline and shuttling of redox equivalents from the cytosol to mitochondria. The impact of the proline cycle goes beyond regulating proline levels. In this review, we focus on recent evidence of how the proline cycle regulates redox status in relation to other redox shuttles. We discuss how the interconversion of proline and glutamate shuttles reducing power between cellular compartments. Spatial aspects of the proline cycle in the entire plant are considered in terms of proline transport between organs with different metabolic regimes (photosynthesis versus respiration) Furthermore, we highlight the importance of this shuttle in the regulation of energy and redox power in plants, through a particularly intricate coordination, notably between mitochondria and cytosol.

Automated summary

Proline, an amino acid known for its role in proteins and osmotic regulation, has been found to have additional functions such as regulating redox balance and energy status. The well-described proline cycle in animals and plants is responsible for proline accumulation and redox equivalent transfer. This cycle not only affects proline levels, but also facilitates the transfer of reducing power between cellular compartments.