Linked from
The 9 pages that link to Protein phosphorylation, each with the reason it gives.
PhosphateRelated: Adding phosphate can alter a protein’s activity, location, or interactions.
Protein kinaseRelated: It is the modification protein kinases catalyze.
Cyclin-dependent kinaseRelated: CDKs regulate targets by adding phosphate groups to them.
ThreonineRelated: Protein kinases can phosphorylate threonine's hydroxyl group.
Biochemical cascadeRelated: Kinase cascades pass activation by phosphorylating downstream proteins.