Table 3.
Kinetic parameters, Vmax and KM, of tyrosine hydroxylase activity for the substrate (L-tyrosine) and the cofactor (6-BH4)
|
L-tyrosine |
6-BH4 |
|||||||
|---|---|---|---|---|---|---|---|---|
| WT | α2AKO | α2BKO | α2CKO | WT | α2AKO | α2BKO | α2CKO | |
| Vmax (nmol/mg protein/h) | 28±1 | 31±2 | 27±1 | 28±1 | 25±1 | 24±3 | 26±1 | 26±2 |
| KM (μM) | 106±20 | 102±25 | 97±12 | 134±19 | 124±15 | 137±13 | 101±12 | 126±9 |
Abbreviations: KM, Michaelis constant; Vmax, maximum velocity; 6-BH4, 6-methyl-5,6,7,8-tetrahydropterine.
Enzyme assay was performed with adrenal homogenates obtained from WT mice and KO mice for each of the three α2-adrenoceptor subtypes (α2A, α2B and α2C). Values are presented as mean±s.e.m. (n=4).