According to Wikipedia, Each PKA is a holoenzyme that consists of a regulatory subunit dimer with each regulatory subunit being bound to a catalytic subunit. As far as I know there are usually more than two subunits, for example, in Drosophila, there are two regulatory subunits(R1 and R2) and three catalytic subunits(C1-C3). I wonder (1) the dimer is hetero- or homo-? (2) what is the difference between different subunits or combination for their function?
In humans there are three C subunits (alpha, beta and gamma) with a bunch of splice variants (around 18 in total) and four R subunits (I alpha, I beta, II alpha and II beta). Dimers of R are supposed to be homo- (although some people think there are heterodimers which is very questionable). Not too much known about distribution of C isoforms (as they are very similar). R-subunits have different expression in different tissues and clearly regulate different processes but how do they do that is often unclear. Most probably they form bigger complexes with other proteins (substrates and phosphatases). One of them with RII beta was recently discussed in Science (2012) 335:712. Finally, nobody knows which R prefers which C, almost all works were done with C alpha.
Regards.
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