among various agonists , isoproterenol was the most potent activator of enzyme activity ( ka = 3.4 x 10 ( -7 ) m ) , followed in order by epinephrine ( ka = 2.7 x 10 ( -6 ) m ) , norepinephrine ( ka = 2.1 x 10 ( -5 ) m ) , and phenylephrine ( ka greater than 10 ( -4 ) m ) .
C0014563
epinephrine
C0028351
norepinephrine