User:TBwichem/Phototropin

Additional information
Phototropins also regulate the movement of chloroplasts within the cell, notably chloroplast avoidance. It was thought that this avoidance serves a protective function to avoid damage from intense light, however an alternate study argues that the avoidance response is primarily to increase light penetration into deeper mesophyll layers in high light conditions.

Enzyme Activity
Phototropins have two distinct light, oxygen, or voltage regulated domains (LOV1, LOV2) that each bind flavin mononucleotide (FMN). The flavin mononucleotide is noncovalently bound to a LOV domain in the dark, but becomes covalently linked upon exposure to suitable light. The formation of the bond is reversible once light is no longer present. The forward reaction with light is not dependent on temperature, though low temperatures give increased stability of the covalent linkage, leading to a slower reversal reaction.

Light excitation will lead to a conformational change within the protein, which allows for kinase activity. There is also evidence to suggest that phototropins undergo autophosphorylation at various sites across the enzyme. Phototropins trigger signaling responses within the cell, but it is unknown which proteins are phosphorylated by phototropins, or exactly how the autophosphorylation events play a role in signaling.

Phototropins are typically found on the plasma membrane, but some phototropins have been found in substantial quantities on chloroplast membranes. One study found that phototropins on the plasma membrane play a role in phototropism, leaf flattening, stomatal opening, and chloroplast movements, while phototropins on the chloroplasts only partially affected stomatal opening and chloroplast movement, suggesting that the location of the protein in the cell may also play a role in its signaling function.