Kinetic properties of mesencephalic tyrosine hydroxylase (TH) were investigated in three highly inbred mouse strains: BALB/cJ, C57BL/6ByJ and CXBI/ByJ. A significant (P < 0.005) genetic variation was found among the apparent maximal velocities of the enzyme reaction (V(max)) without any significant differences in the values of apparent Michaelis-Menten constants (K(m)). Moreover, a biphasic pattern was found when TH activity was measured as the function of the cofactor (6-methyl-5,6,7,8-tetrahydropterin) concentration, indicating the presence of both the phosphorylated (high-affinity, HA) form and the non-phosphorylated (low-affinity, LA) form of TH. Again, there was no significant genetic source of differences among the K(m) values. However, the V(max) of the LA form was significantly higher in BALB/cJ than in the other two strains, whereas C57BL/6ByJ and CXBI/ByJ differed in the V(max) values of the HA form of TH.
|Number of pages||9|
|Publication status||Published - Jan 1 1989|
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