Hi,
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We hope that you would be able to find answers to your questions over here, and also help others to find answers to their question.
As per you question,
I found an article from over 20 years ago dealing with an isolation of troponin (which is also a phosphorilated protein) from heart.
Here is the link to the article.
I hope it would help you.
www.blackwell-synergy.com/doi/ pdf/10.1111/j.1432-1033.1988.tb14285.x
Guy