The phosphorylation sites of troponin T from white skeletal muscle and the effects of interaction with troponin C on their phosphorylation by phosphorylase kinase

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Abstract
The phosphorylation of troponin T from rabbit white skeletal muscle is catalyzed by phosphorylase kinase, but not at a significant rate by bovine cycle AMP-dependent protein kinase. The amino acid sequences adjacent to the 3 major phosphorylation sites of troponin T were determined. The serine in the N-terminal peptide (Asx,SerP,Glx)Glu-Val-Glu, is that phosphorylated (SerP, phosphoserine) when the troponin complex is isolated. The other 2 sites of phosphorylation are located in the sequence Ala-Leu-(Ser,SerP)-Met-Gly-Ala-Asn-Tyr(Ser,SerP)Tyr. When troponin T is phosphorylated in the presence of troponin C, the extent of phosphorylation at each site is considerably decreased. CNBr fragments of troponin T are also phosphorylated by phosphorylase kinase, but the rate of phosphorylation at each site in the CNBr fragments is considerably slower than in the native protein. Troponin C probably interacts with troponin T in the region containing the 2 closely situated phosphorylation sites.