It was noteworthy that this [K.sub.a] value was somewhat higher than the [K.sub.m] values commonly reported for ATP in the protein kinase A catalysed reaction of peptide phosphorylation, most often ranging between 5 [micro]M and 20 pM.
Differently from the results for ATP, the affinity of the free protein kinase A for peptides was rather diverse, and the [K.sub.b] values, ranging from 2 [micro]M to 6 mM (see Table 1), were obtained for a series of selected substrates.
Interaction factor [alpha] for protein kinase A substrates
In the present study, we used this very straightforward kinetic analysis for the protein kinase A catalysed reaction of phosphorylation of peptide substrates.
As phosphorylation of different peptides was studied, the results provided a unique possibility of analysing the interrelationship between the substrate binding effectiveness and the allosteric behaviour of protein kinase A. This analysis revealed that a more efficient substrate binding was accompanied by a more significant allosteric effect.
Perhaps protein kinase A is an example of such highly dynamic protein.
This should certainly complicate theoretical analysis of the substrate specificity of protein kinase A and the specificity of bisubstrate enzymes in general.
This means that at least this part of the substrate specificity of protein kinase A that is based on the recognition of the primary structure of phosphorylatable peptides is amplified by allostery.
An allosteric effect was found in the peptide phosphorylation reaction catalysed by the catalytic subunit of cAMP dependent protein kinase (protein kinase A), which is a monomeric bi-substrate enzyme.
Allosteric cooperativity in protein kinase A. Proc.
Allosteric cooperativity in inhibition of protein kinase A catalytic subunit.