Histone kinases and cyclic AMP-binding capacity of nuclei of human tonsillar lymphocytes

Specific substrate for histone kinase II: a synthetic nonapeptide

Based on the previously determined intrinsic substrate specificity of histone kinase II, a nonapeptide was synthesized which was a specific substrate for this enzyme. The Vmax value of phosphorylation of the peptide (Ala-Ala-Ala-Ser-Phe-Lys-Ala-Lys-Lys-amide) was about the same as that for H1 histone and the apparent Km for the phosphorylation of the peptide was 0.2 mM, an order of magnitude higher than that for H1 histone. H1 histone inhibited the phosphorylation of the peptide, while the peptide did not inhibit the phosphorylation of H1 histone. In the crude extracts of calf thymus, spleen and liver, histone kinase II was the only enzyme which phosphorylated the synthetic peptide. The rate of phosphorylation of this peptide was used to determine the activity of histone kinase II in the crude extracts of several tissues obtained from different species.

The site of histone H2b phosphorylated by a cyclic nucleotide independent histone kinase

A cyclic nucleotide independent histone kinase was demonstrated in bovine thymus extract. This enzyme was very similar to that found previously in the cytoplasm and nucleus of human tonsillar lymphocytes (Faragó et al., 1973, Biochim. Biophys. Acta 297, 517 and 1974, ibid 370, 459). High-performance liquid chromatography of the tryptic phosphopeptides of calf thymus histones H1 and H2b phosphorylated by the histone kinase or by the catalytic subunit of cylic AMP dependent protein kinase showed that the intrinsic substrate specificity of these enzymes differed significantly. Under our experimental conditions the histone kinase phosphorylated preferentially the Ser-32 residue, and it did not phosphorylate the Ser-36 residue of histone H2b, while Ser-36 was phosphorylated preferentially by the cyclic AMP dependent protein kinase. A peptide containing the amino acid sequence of histone H2b from Gly-26 to Lys-34 (Gly-Lys-Lys-Arg-Lys-Arg-Ser-Arg-Lys-Ala) was synthesized. This peptide was a competitive inhibitor of histone H1 phosphorylation by the histone kinase and it was also a substrate for this enzyme.

Low molecular weight cyclic AMP binding protein isolated from the extract of human tonsillar lymphocytes

A protein fraction of molecular weight 33,000-36,000 accounted for about 40% of the cyclic AMP binding capacity of the cytoplasmic extract of human tonsillar lymphocytes. This cyclic AMP binding fraction (designated as R' protein [10]) proved to be a proteolytic fragment of the regulatory subunit of the cyclic AMP-dependent protein kinase. The Scatchard plot of cyclic AMP binding by the isolated R' fraction indicated positive cooperativity. 50% saturation of the cyclic AMP binding sites was achieved at about 4 . 10(-9) M cyclic AMP. An upward concave curve was obtained in the Scatchard plot of cyclic GMP binding by the R' protein. These results strongly suggest that more than one molecule of cyclic nucleotide can be bound by one molecule of the R' protein. The R' protein could not be detected in the physiological salt extract of isolated nuclei in which type I cyclic AMP-dependent protein kinase was the dominating isoenzyme (according to the terminology used by Corbin, S.D., Keely, S.L. and Park, C.R. (1975) J. Biol. Chem. 250, 218-225). The cytoplasm of cells contained a higher amount of type II than type I regulatory subunit. In the cytoplasm the predominant part of RII was present in the dissociated state in all preparations, while when the RII was found in the nucleus it was mainly in the holoenzyme form. The R' protein presumably from the dissociated type II regulatory subunit.

Cyclic nucleotide binding properties and molecular forms of the cyclic-AMP-dependent protein kinase from bovine eye lens

The activity of the cyclic-AMP-dependent protein kinase found in the crude extract of bovine eye lens cortical fibers was increased by 10(-6) M cyclic AMP or 10(-5) M cyclic GMP to the same extent, However, the interaction between cyclic AMP and cyclic GMP in the course of binding to the cyclic-AMP-dependent protein kinase did not seem to be competitive. Scatchard analysis of cyclic GMP binding by the crude extract indicated the presence of two type of cyclic GMP binding sites (Kd1 about 2 . (10(-7) M, Kd2 about 5 . 10(-6) M). Different species of cyclic nucleotide binding fractions were separated by Sephadex G-200 gel chromatography of the crude extract. The bulk of the low affinity cyclic GMP binding activity was found in the exclusion volume. The cyclic-AMP-dependent protein kinase eluted in two fraction (apparent molecular weight 300 000 and 150 000) and both protein kinase fractions were accompanied by the high affinity cyclic GMP binding activity. However, the ratios of this activity to the cyclic AMP binding activity were different in the two fraction, suggesting that different molecular weight forms of the holoenzyme had different cyclic nucleotide binding properties.

Two types of cyclic GMP binding site associated with the cyclic AMP-dependent protein kinase from lymphocytes

Low- and high-affinity binding sites for cyclic GMP were found to be associated with the cyclic AMP-dependent protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) from human tonsillar lymphocytes, but neither of them was identical with the cyclic AMP binding site. The enzyme activated by cyclic GMP phosphorylated the same site of calf thymus H2b histone as the cyclic AMP activated enzyme; however, more complex kinetics of activation were found with cyclic GMP. Two classes of cyclic GMP binding site were demonstrated by kinetic analysis of cyclic [3H]GMP binding in the enzyme preparations eluted by 0.1 M potassium phosphate (pH 7.0) from DEAE cellulose. The high-affinity cyclic GMP binding site (Kd about 4 . 10(-8) M) belonged to some complex form of the protein kinase, as evidenced by the mutual inhibition of cyclic AMP binding and high affinity cyclic GMP binding. However, the high-affinity cyclic GMP binding site disappeared on Sephadex G-100 gel chromatography of the enzyme preparation, whereas the cyclic AMP binding activity was recovered quantitively as separate fractions. The low-affinity cyclic GMP binding site (Kd 2--5 . 10(-6) M) was demonstrated by the inhibitory effect of 10(-5) M cyclic GMP on cyclic AMP binding in each cyclic AMP binding fraction obtained by gel chromatography. However, cyclic AMP did not inhibit the binding of cyclic GMP to the low-affinity binding site.

Nucleoside-dependent protein kinase from Trypanosoma gambiense

A nucleoside-dependent protein kinase (EC 2.7.1.37) was partially purified from Trypanosoma gambiense, the pathogenic agent of sleeping sickness. This enzyme catalyzes the phosphorylation of histone and protamine. Various nucleosides at the concentration of 10(-4) M stimulated the histone kinase activity about two-fold, whereas cyclic AMP and cyclic GMP were without effect. The pH-optimum for histone phosphorylation was at about pH 7.0. The enzyme activity absolutely depends on Mg2+, Mn2+ or Co2+. The apparent Km-value for histone was 0.3 mg/ml and those for ATP were 2 - 10(-4) M and 6 - 10(-5) M in the absence or presence of 10(-4) M adenosine respectively. IDP and ADP complete with ATP. The inhibition constants were calculated to be 2 - 10(-4) M and 2.5 - 10(-4) M, respectively. The molecular weight of the histone kinase was found to be 95 000 by gel filtration and 88 000 by sedimentation in a sucrose gradient.

Nuclear protein kinases from murine cells

Three protein kinase activities are found in nuclei from three different murine cells (Ehrlich ascites cells, mouse L cells and rat glioma cells). Two of these activities are soluble, one is bound to chromatin. The soluble enzymes are similar, if not identical, to the cytoplasmic protein kinases. The chromatin-bound, adenosine-cyclic-3':5'-monophosphate-independent enzyme is not found in the cytoplasm. This enzyme is composed of one subunit with a molecular weight of 80000-90000. Some biochemical properties of this enzyme are described. A brief description of a nuclear enzyme, which dephosphorylates phosphorylated histones, is also given.