Cyclic nucleotide-dependent protein kinases in the neural tissue of the honeybee Apis mellifera

Two cyclic nucleotide-dependent protein kinases have been purified and characterized from neural tissue of the honeybees Apis mellifera. The first kinase ($\text{M}{}_{\mathrm{<mtext>r</mtext>}}\text{= 180,000}$) has a tetrameric structure with two regulatory and two catalytic subunits that dissociate upon addition of cAMP. The regulatory subunits exist in phospho- and dephosphoform, which show electrophoretic mobilities in SDS-PAGE corresponding to $\text{M}{}_{\mathrm{<mtext>r</mtext>}}\text{= 50,000}$ and $\text{M}{}_{\mathrm{<mtext>r</mtext>}}\text{= 49,000}$, respectively. The values for half-maximal stimulation using histone IIA as substrate is 3.3 nM cAMP or 33 nM cGMP. The second cyclic nucleotide-dependent protein kinase, with $\text{M}{}_{\mathrm{<mtext>r</mtext>}}\text{= 80,000}$, is dimeric with a regulatory (phosphoform $\text{M}{}_{\mathrm{<mtext>r</mtext>}}\text{= 36,000}$) and a catalytic subunit. Detection of this regulatory subunit in heads and brains homogenized in presence of SDS, TCA and various protease inhibitors supports strong evidence that the dimeric kinase is no artefact but exists in vivo. In contrast to the regulatory subunit of the tetrameric kinase, the regulatory subunit of the dimeric kinase is localized only in the soluble fraction.