Biomedical subjects

C R Park

Publications and source records attributed to C R Park.

At least 55 records · Page 3Linked to original sources

PubMed1975

Regulation of adenosine 3:5-monophosphate-dependent protein kinase.

The effects of epinephrine, glucagon, insulin and 1-methyl-3-isobutylxanthine on adenosine 3:5-monophosphate (cAMP)-dependent protein kinase activity were investigated in the perfused rat heart. The conditions for homogenization of heart tissue and assay of protein kinase are described. The activation state of the enzyme is expressed as the ratio of the rate of phosphorylation of histone in the absence to that in the presence of 2 mu-M cAMP. This activity ratio is stable in crude homogenates over 15 min of incubation; it is not affected by up to 30-fold dilution of the tissue volume. The ratio is elevated to a variable degree in hearts taken immediately from the animal but falls to a stable, basal level of 0.15 to 0.20 after 15 min of perfusion in vitro. An optimal concentration of epinephrine (10 mu-M) in the perfusate elevates cAMP from 0.5 to 1.3 nmol per g of tissue and increases the protein kinase activity ratio from 0.20 to 0.65. When hearts are perfused with a steady, submaximal concentration of epinephrine (0.4 mu-M), the level of cAMP and the protein kinase activity ratio rise in parallel within 15 s and remain elevated for at least 10 min. When epinephrine is removed from the perfusion medium, the level of cAMP and enzyme activity ratio decline rapidly to basal levels. Both glucagon and the phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine also increase the cardiac cAMP levels and protein kinase activity ratio in a dose-dependent manner. Glucagon acts as rapidly as does epinephrine whereas 1-methyl-3-isobutylxanthine requires at least 30 s before any effect can be observed. Insulin by itself does not significantly affect the cyclic nucleotide level or enzyme activity. The hormone has not been observed to lower the cAMP level or protein kinase activity in the heart under any conditions tested. In concentrations of 10 microunits per ml or greater, it does, however, cause a slight rise in the tissue level of cAMP and the protein kinase activity when these have been elevated to intermediate levels by exposure to epinephrine. This effect could only be observed when hearts were treated with catecholamine and could not be detected with glucagon or 1-methyl-3-isobutylxanthine. In all cases tested, slight increases in the protein kinase activity ratio (from 0.2 to 0.3) were accompanied by much greater increases in the amount of phosphorylase in the a form (20% to 70%). It was observed that at perfusion times greater than 3 min, there was a significant reduction in phosphorylase activity even though both the cAMP level and protein kinase activity remained elevated. In these studies, changes in the protein kinase activity correlate well with the tissue cAMP levels under all conditions tested.

Adenosine Triphosphate↗

PubMed1975

The distribution and dissociation of cyclic adenosine 3':5'-monophosphate-dependent protein kinases in adipose, cardiac, and other tissues.

In crude extracts of adipose tissue the protein kinase dissociates slowly at 30 degrees into regulatory and catalytic subunits in the presence of 700 mug per ml of histone or 0.5 M NaCl. If the kinase is first dissociated by adding 10 muM adenosine 3':5'-monophosphate (cAMP), reassociation occurs instantaneously after removal of the cAMP by Sephadex G-25 chromatography. In contrast, in crude xtracts of heart, the protein kinase dissociates rapidly in the presence of 700 mug per ml of histone or 0.5 M NaCl and reassociates slowly after removal of cAMP. These differences are accounted for by the existence of two types of protein kinases in these tissues, referred to as types I and II. DEAE-cellulose chromatography of extracts of adipose tissue produces only one peak of cAMP-dependent protein kinase activity (type II) which elutes between 0.15 and 0.25 M NaCl. Similar chromatography of heart extracts resolves enzyme activity into two peaks; a type I enzyme which elutes between 0.05 and 0.1 M and predominates (greater than 75% of total activity), and a type II enzyme which elutes between 0.15 and 0.25 M NaCl. The dissociation properties of the types I and II enzymes from heart and adipose tissue are retained after partial purification by DEAE-cellulose and Sepharose 6B chromatography. Rechromatography of the separated peaks of the cardiac enzymes does not change the elution pattern. Sucrose density gradient centrifugation and gel filtration studies indicate that the molecular weights of these enzymes are very similar. The type II enzyme isolated by DEAE-cellulose chromatography of heart extracts resembles the adipose tissue enzyme, i.e. it undergoes slow dissociation at 30 degrees in the presence of histone or 0.5 M NaCl. The adipose tissue kinase and the heart type II kinase are not identical, however, since they do not elute at exactly the same point on DEAE-cellulose columns. A survey of several tissues indicates the presence of type I and II protein kinases similar to the enzymes in adipose tissue and heart as determined by DEAE-cellulose chromatography of crude extracts and by dissociation of the enzymes with histone. The presence of MgATP prevents dissociation of type I enzyme from heart by 0.5 M NaCl or histone. The profile of the enzyme on DEAE-cellulose, however, is not changed...

Adenosine Triphosphate↗

PubMed1975

On the question of translocation of heart cAMP-dependent protein kinase.

Rat hearts were perfused with epinephrine and/or 1-methyl-3-isobutylxanthine for 2 min. These agents raised the concentration of cAMP and increased the fraction of cAMP-dependent protein kinase (EC 2.7.1.70) in the active form. However, the content of cAMP-dependent protein kinase in the soluble fraction of homogenates of these hearts was reduced and the amount in the particulate fraction was increased. A similar redistribution was obtained by adding cAMP to homogenates of control hearts. The reduction in soluble protein kinase content was due to apparent binding of the free catalytic subunit of the enzyme to particulate material (12,000 times g pellet) in media of low ionic strength (smaller than 100 mM KCl). The amount bound was, therefore, proportional to the dissociation of the holoenzyme. The binding was not altered by prior boiling or trypsin treatment of the particulate material, but it was prevented or reversed by the addition of 150 mM KCl. The catalytic subunit of the protein kinase from heart also bound to particulate fractions from liver or Escherichia coli and to various denatured proteins. These findings suggest that the protein kinase activity of membranes and particulate fractions has frequently been overestimated, since isolation of particulate materials has usually been carried out at low ionic strength. The data also imply that intracellular translocation of the protein kinase catalytic subunit, at least in heart tissue, is of questionable physiological significance.

Animals↗

PubMed1975

Hormonal regulation of adenosine 3',5'-monophosphate-dependent protein kinase.

There appear to be two classes of protein kinases in rat heart and adipose tissue, types I and II. Type I elutes from DEAE-cellulose at smaller than 0.1 M NaCl and type II at greater than 0.1 M NaCl. The type I enzyme is more readily dissociated by salt or histone than is the type II enzyme. If the type I kinase is first dissociated by cAMP, the subunits reassociate very slowly at 0 degrees C on removal of the cAMP by Sephadex G-25 chromatography, whereas those of type II reassociate very rapidly. Rat heart contains mostly type I and a small amount of type II enzyme, whereas adipose tissue contains almost exclusively the type II enzyme. The adipose tissue enzyme resembles the heart type II kinase in all of the above properties, although the two enzymes are not identical as indicated by slight differences in elution patterns from DEAE-cellulose columns. Incubation of rat epididymal adipose tissue with low concentrations of epinephrine (0.11 muM) increases glycerol production and the fraction of the protein kinase in the active form (activity ratio). The change in cAMP under these conditions is not statistically significant. The presence of insulin inhibits the epinephrine effect on glycerol production and protein kinase but has no measurable effect on cAMP levels. Incubation of adipose tissue with high epinephrine concentrations (11 muM) increases the cAMP level, the protein kinase activity ratio, and glycerol production. Under these conditions insulin decreases the cAMP level and kinase activity ratio but does not reduce glycerol production. The data suggest that very small changes in the tissue cAMP level, undetectable by the assay method, are magnified during the stepwise activation of glycerol output aided possibly by cooperative effects between cAMP and protein kinase. The procedure developed for determining the state of activation of the cAMP-dependent protein kinase in adipose tissue must be modified by reducing the salt concentration of the buffers in order to carry out similar studies in the heart. This reflects the different types of protein kinase in the two tissues. The addition of charcoal to crude extracts of heart prevents protein kinase activation by added cyclic AMP. Charcoal should therefore prevent any activation that could occur if any sequestered cAMP were released during homogenization. Charcoal addition thereby provides a means to distinguish intracellular cAMP activation of the kinase from that which might occur following cell rupture. If epinephrine-perfused hearts are homogenized in the presence of charcoal, epinephrine stimulation of the protein kinase is only slightly decreased. This indicates that the protein kinase is activated intracellularly by cAMP and suggests that all of the cAMP in the cell is available to the protein kinase; i.e., cAMP is not released during homogenization.

Adipose Tissue↗

PubMed1974