Step I JAK STAT pathway

[Reperfused]

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Does JAK have tyrosine activity or not?
UW qid 1121 (choice A explanation) says it has tyrosine kinase activity.
UW qid 994 (choice B explanation) says it lacks tyrosine kinase activity.

Also, it is a cytoplasmic protein and NOT a transmembrane receptor, right?

 

[DetectiveAlonzo]

JAK stat is a NON-receptor tyrosine kinase.

It does have that activity.

Yes. It is a cyotplasmic protein.

 

[Reperfused]

JAK stat is a NON-receptor tyrosine kinase.

It does have that activity.

Yes. It is a cyotplasmic protein.

Thanks. That's what I thought.
But there's a discrepancy between the two UW questions I mentioned above. Any idea why? Or is it just a mistake in UW?

 

[chromuffin]

Thanks. That's what I thought.
But there's a discrepancy between the two UW questions I mentioned above. Any idea why? Or is it just a mistake in UW?

If you look at the diagram in QID 994, it is referring to the intrinsic kinase domain. JAK has tyrosine kinase activity as a cytoplasmic enzyme, not as an enzyme bound to the intrinsic domain of a receptor. So UWorld has not made a mistake. JAK has tyrosine kinase activity because it is a cytoplasmic tyrosine kinase. It doesn't work by being bound by anything; therefore, it is not a receptor tyrosine kinase. Being a cytoplasmic enzyme could either mean it is bound to an intrinsic domain of a receptor (which is what QID994 is getting at) or it can just be found freely in the cytoplasm (like it is). I can see the confusion though.

 

[Reperfused]

If you look at the diagram in QID 994, it is referring to the intrinsic kinase domain. JAK has tyrosine kinase activity as a cytoplasmic enzyme, not as an enzyme bound to the intrinsic domain of a receptor. So UWorld has not made a mistake. JAK has tyrosine kinase activity because it is a cytoplasmic tyrosine kinase. It doesn't work by being bound by anything; therefore, it is not a receptor tyrosine kinase. Being a cytoplasmic enzyme could either mean it is bound to an intrinsic domain of a receptor (which is what QID994 is getting at) or it can just be found freely in the cytoplasm (like it is). I can see the confusion though.

Thanks a lot!
It totally makes sense now. I knew I was missing something cuz it's hard to believe that UW would have a mistake.