| Autor: |
C J, Yuan, C Y, Huang, D J, Graves |
| Rok vydání: |
1993 |
| Předmět: |
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| Zdroj: |
The Journal of biological chemistry. 268(24) |
| ISSN: |
0021-9258 |
| Popis: |
Phosphorylase kinase is shown to be a dual specificity kinase. The specificity of phosphorylation is determined by divalent cation. Mg2+ causes seryl phosphorylation of phosphorylase b, but Mn2+ activates tyrosine phosphorylation of angiotensin II. In contrast to seryl phosphorylation, the tyrosine kinase activity of holoenzyme is not regulated by Ca2+. Preincubation of the holoenzyme with Ca2+, Mg2+ and ATP that causes autophosphorylation activates tyrosine kinase activity. The tyrosyl kinase activity is a property of the gamma subunit. Addition of varying amounts of Mn2+ to a truncated form of the gamma subunit of phosphorylase kinase containing MgATP inhibits serine kinase but activates tyrosine kinase activity. This result along with an oxidative reaction caused by Cu2+ and site-directed mutagenesis of the putative catalytic base inhibiting both serine and tyrosine kinase activity suggest that one active site is involved in both activities. Kinetic studies with Mn2+ and ATP show that Km for nucleotide is not changed with a seryl or tyrosyl substrate. The Vm values are different, and the value for tyrosyl phosphorylation is similar to other tyrosyl kinases. We propose two conformations for the active site; one favors seryl phosphorylation, and the second tyrosyl phosphorylation is caused by the binding of divalent cation at a second metal ion binding site. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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