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Biomedical subjects

S Kakiuchi

Publications and source records attributed to S Kakiuchi.

At least 73 records · Page 4Linked to original sources
PubMed1978

Identification of an activator protein for myosin light chain kinase as the Ca2+-dependent modulator protein.

Myosin light chain kinase which phosphorylates g2 light chain of skeletal muscle myosin requires an activator for the activity (Yazawa, M., and Yagi, K (1977) J. Biochem. (Tokyo) 82, 287-289). This activator has now been identified as the modulator protein known to be a Ca2+-dependent regulator for phosphodiesterase, adenylate cyclase, and ATPases. The identification is based on the quantitative cross-reactivity of muscle activator protein and brain modulator protein in activating myosin light chain kinase and brain phosphodiesterase and identical properties of both proteins in regard to sensitivities to Ca2+, UV absorption spectra, UV absorption difference spectra with or without Ca2+, and mobilities upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the presence of modulator protein, the activity of myosin light chain kinase was reversibly controlled by the physiological concentration of Ca2+. We suggest that two Ca2+-receptive proteins, i.e. modulator protein and troponin-C, may play roles in the contraction-relaxation cycle of skeletal muscle.

Animals↗
PubMed1978

Effect of sodium ion on levels of cyclic adenosine 3',5'-monophosphate in guinea pig cerebral slices.

Accumulation of cyclic AMP was studied in guinea pig cerebral slices when Na+ levels in the bathing medium were varied or agents which affect tissue Na+ content were added. When NaCl was gradually replaced with Tris-HCl or choline chloride, cyclic AMP formation was progressively enhanced. ;when Na+ was below 30 mM, cyclic AMP formation reached the maximum (approximately 30 fold), but this increment was not blocked by tetrodotoxin. The stimulatory effect of high K+ was nearly linear over 120 mM and became much more prominent when Na+ also was not blocked by tetrodotoxin. Ouabain (10(-4) M), electrical pulses and glutamate (5 x 10(-3) M), each stimulated cyclic AMP formation about 17-, 7- and 5-fold, respectively. Tetrodotoxin (2 x 10(-6) M) completely blocked the effects of electrical pulses and partially blocked the effects of glutamate and oubain. It is suggested that the increase of cyclic AMP in cerebral cortical slices may be related to the decrease in Na+ gradient across the cell membrane.

Animals↗
PubMed1978

Membrane-bound forms of Ca2+-dependent protein modulator: Ca2+-dependent and independent binding of modulator protein to the particulate fraction from brain.

Ca2+-dependent binding of modulator protein to the particulate fraction was studied. The particulate fraction from one gram of rat brain bound in a Ca2+-dependent fashion 144 microgram of modulator protein, representing more than one third of the total soluble modulator protein in this tissue. The binding site was present in both the mitochondrial and microsomal fractions, the specific activity of the microsomes being the higher. The binding was reversible with a physiological concentration of Ca2+, and was temperature-dependent, and the site can be saturated with modulator protein (4.5 microgram modulator protein per mg of microsomal protein). Tryptic digestion of the membranes caused complete disappearance of the binding activity, but heat-treatment for 5 min at 70 degrees C caused only 40% loss of activity. The binding site may be a known or unknown enzyme(s), the activity of which is regulated by Ca2+ and modulator. Alternatively, this binding site may be a nonenzymic protein that regulates the concentration of free modulator protein in the cell.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Evidence for differences in protein kinase modulator and and phosphodiesterase activator.

Both protein kinase modulator and phosphodiesterase activator activities were present in the supernatant fluid of a homogenate of bovine brain. These were separated on a DEAE-cellulose column chromatography. Separation was also achieved by an isoelectrofocusing fractionation of the supernatant fluid, isoelectric points of proteins kinase modulator and phospodiesterase activator being 4.25 and 4.44, respectively. Phospodiesterase activator was purified from bovine brain to an apparent homogenity by a procedure which did not involve a drastic treatment such as boiling. The purification of phosphodiesterase activator resulted in removing the protein kinase modulator activity and the ratio of the activity of protein kinase modulator to that of phosphodiesterase activator in the sample decreased as the purification proceeded.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Phosphoprotein phosphatases for myelin basic protein in myelin and cytosol fractions of brain.

Phosphoprotein phosphatase (phosphoprotein phosphohydrolase EC 3.1.3.16) activity for myelin basic protein was found to be present in the myelin fraction of rat brain. The enzyme activity was in a latent form and solubilized by 0.2% Triton X-100 treatment with about 50% increase of activity. The cytosol fraction from bovine brain also had phosphoprotein phosphatase activity for myelin basic protein, which was resolved into at least two peaks of activity on DEAE-cellulose column chromatography. Myelin basic protein was the best substrate for both the solubilized myelin fraction and the cytosol enzymes among the substrate proteins tested. The Km values of the solubilized myelin fraction were 4.2 muM for myelin basic protein, 7.4 muM for arginine-rich histone, 8.0 muM for histone mixture and 14.3 muM for protamine, respectively.

Animals↗
PubMed1975

Multiple cyclic nucleotide phosphodiesterase activities from rat tissues and occurrence of a calcium-plus-magnesium-ion-dependent phosphodiesterase and its protein activator.

1. Supernatant fluids from rat cerebral cortex, cerebellum, kidney, heart and liver contained more phosphodiesterase activity hydrolysing cyclic GMP than that hydrolysing cyclic AMP when assayed with sub-saturating concentrations of substrate. 2. These activities were resolved into several fractions by Sephadex G-200 gel filtration; no two tissues had similar activity profiles. 3. With every tissue examined, a fraction (fraction II) with a molecular weight of about 150,000 was obtained which hydrolysed cyclic GMP preferentially at sub-saturating substrate concentrations in the presence of micromolar concentration of Ca2+, millimolar concentration of Mg2+ and a protein activator. 4. The activity of fraction II accounted for about 60 percent in liver, more than 80 percent in heart and cerebellum, and almost 100 percent in cerebral cortex of the total activity for cyclic GMP hydrolysis, calculated from the activity profiles. 5. Km values of fraction II samples from kidney, heart and liver for cyclic GMP were 1.3, 1.7 and 5 muM respectively. 6. 3-Isobutyl-1-methylxanthine inhibited hydrolysis of cyclic GMP by fraction II with an I50 value of 3muM for heart and liver and 50 muM for cerebrum. 7. The activator protein, with an estimated molecular weight of about 30,000 was isolated from all the tissues listed in 1.8. The concentrations of activator protein and of the isolated enzyme, fraction II, did not correspond exactly.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Ca-2+/Mg-2+-dependent cyclic nucleotide phosphodiesterase and its activator protein.

(1) Ca-2+/Mg-2+-dependent cyclic nucleotide phosphodiesterase was found in the supernatant fluids of a variety of tissues, including cerebral cortex, cerebellum, kidney, liver, and heart. (2) this enzyme required Ca-2+, Mg-2+, and an activator protein (PAF) for the activity. In the presence of these ingredients the enzyme hydrolyzed cyclic GMP preferentially when incubated with a low concentration (0.4 muM) of substrate. (3) The enzyme devoid of PAF was eluted in fraction II with a molecular weight of approximately 150,000 after Sephadex G-200 gel filtration of the supernatant fluids using medium containing EGTA. PAF thus separated from the enzyme was eluted in a fraction corresponding to a molecular weight of approximately 28,000 by gel filtration. Stimulation of the activity of fraction II by Ca-2+ was completely dependent on the addition of PAF. (4) Formation of an active enzyme-PAF complex with an estimated molecular weight of 200,000 was demonstrated by gel filtration of a mixture of the enzyme and PAF in medium containing Ca-2+. It is likely that the activity of the Ca-2+/Mg-2+ in a concentration range of approximately 1 to 10 muM, as shown in the following equation: [Enzyme] inactive + PAF + Ca-2+ in equilibrium [enzyme - PAF - Ca-2+] active. More than one PAF protein may bind to one molecule of enzyme to form an active complex. Equilibrium of the above equation is probably determined mainly by the intracellular concentration of Ca-2+ in vivo. (5) The enzyme-PAF complex was more labile after heat treatment than the free form of enzyme. (6) PAF was isolated from all tissues listed in (1). The levels of PAF and of fraction II did not correspond exactly.

Animals↗
PubMed1973

Regulation of nucleoside cyclic 3':5'-monophosphate phosphodiesterase activity from rat brain by a modulator and Ca2+.

Gel filtration of the 40,000 rpm supernatant fraction of a homogenate of rat cerebral cortex on a Sepharose 6B column yielded two fractions: fraction II with the "Ca(2+) plus Mg(2+)-dependent" phosphodiesterase activity and fraction III containing its modulator. The activity of fraction II was stimulated by micromolar concentrations of Ca(2+) and the modulator when present together; the modulator stimulated the activity of fraction II only when the Ca(2+) concentration was above a threshold value (about 2 muM with 0.4-1 muM substrate), and the stimulatory effect of Ca(2+) was dependent upon the presence of the modulator. A possibility is discussed that the modulator may reversibly bind to the enzyme, which by itself is inactive, to form an active enzyme-modulator complex and that Ca(2+) stimulates the activity of phosphodiesterase by shifting the equilibrium between these three species towards the formation of the active enzyme-modulator complex. Although fraction II hydrolyzed both cyclic AMP and cyclic GMP, hydrolysis of the latter was more significantly influenced by Ca(2+) and the modulator than that of the former, and the "Ca(2+) plus Mg(2+)-dependent" phosphodiesterase is likely to be a cyclic GMP enzyme. This conclusion is based on the following evidence: (a) Ca(2+) stimulated hydrolysis of cyclic GMP by fraction II more than that of cyclic AMP. (b) In the presence of Ca(2+) and the modulator, fraction II hydrolyzed cyclic GMP about 8 times faster than cyclic AMP when incubated with 0.4 muM substrate. (c) Half-maximal stimulation of hydrolysis of cyclic GMP was attained at a lower concentration of Ca(2+) (4 muM) than that of cAMP (8 muM). (d) Increase in the concentration of Ca(2+) from 0.06 muM to 12 muM in the presence of the modulator caused a decrease in the K(m) value of cyclic GMP hydrolysis by fraction II from 20 muM to 2 muM accompanied by 4-fold increase in the V(max) value. Under similar conditions, there was only a slight decrease in the K(m) value of cylic AMP hydrolysis (90 muM --> 50 muM), although the V(max) value increased 7-fold. The anomalous shape of the kinetic plot of cyclic GMP hydrolysis became linear when the Ca(2+) concentration was increased in the presence of the modulator. The modulator seems to be a protein, but it is heat stable. It is probably identical to the protein activator of phosphodiesterase first described by Cheung.

Animals↗