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.

P38A S181-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.

P38A S181-p
Regulatory protein:
leptin T74-p
insulin T178-p
long-term_potentiation T190-p
LPA S181-p
NAG-thiazoline Y180-p , S181-p
okadaic_acid Y180-p , S181-p
PUGNAc Y180-p , S181-p
SB202190 S181-p