Kinase, in vitro: 

An enzyme-substrate reaction that occurs in non-living experimental conditions such as a test tube. For example, a purified enzyme is reacted with a substrate protein or mixture of proteins or peptides.

ERK1 S537-p
ERK2 S537-p
 Putative in vivo kinases: 

An enzyme-substrate reaction that occurs within living cells; includes cultured cells, ex vivo samples, and intact organisms. In the case of kinases, the large number of protein kinases in intact cells makes exact identification of the responsible kinase challenging.

ERK1 S537-p
ERK2 S537-p
Regulatory protein:
NAG-thiazoline S545-p
okadaic_acid S545-p
PD98059 S537-p
phorbol_ester S537-p
PUGNAc S545-p
serum S537-p