Phosphorylated Proteins - (Mar/08/2007 )

Why are some proteins phoshporylated but when assayed for actvity not active?

Is it that the there are other phosphorylation sites that could be inhibitory?

Thanks

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phosphorlyations fulfil various tasks: modulation of binding affinities (e.g. CaMKII at T305/T306 increases affinity for CaM several thousand fold), activation of enzyme activity (e.g. c-Src at Y418), inhibition of enzyme activity (e.g. c-Src at Y529)

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Phosphorylation is not the same as activation!

Many proteins are activated in their phosporylated state but some are inactivated.

For example, in glycogen regulation, glycogen synthase kinase 3 and glycogen synthase are both inactivated by phosphorylation, not a simple system to explain...

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Plus, phosphorylation on the same protein can have differencial effects. Take Insulin Receptor as an example. Serine phosphorylation inhibits its activity, wereas tyrosine phosphorylation enhances it.

So it is different for every case

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