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P K Chiang

Publications and source records attributed to P K Chiang.

13 recordsLinked to original sources
PubMed1992

Prejunctional muscarinic receptors in the deep muscular plexus of canine ileum: comparison with smooth muscle receptors.

Prejunctional muscarinic receptors from the deep muscular plexus of canine ileum were studied, and their properties were compared with those of the postjunctional receptors of the circular smooth muscle. In the purified synaptosomal fraction (a fraction containing primarily the axonal varicosities of deep muscular plexus), the muscarinic ligand N-[3H]methylscopolamine labeled an apparently homogenous population of receptors (nH = 1) with a Kd of 2.7 nM and a Bmax of 195 +/- 44 fmol/mg protein (mean +/- S.D., n = 4). These receptors showed a high affinity for the M3/M1-selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (pKi = 7.41); in contrast, the pKi values of pirenzepine (5.60), methoctramine (5.65) and AF-DX 116 (5.21) implied little selectivity for these subtypes. The binding properties of muscarinic receptors in the synaptosomal fraction were different from the binding properties of muscarinic receptors in the purified circular smooth muscle plasma membranes. Most notably, the circular smooth muscle receptors had significantly lower affinity for N-[3H]methylscopolamine (Kd = 16 nM) with a Bmax value of 2088 +/- 276 fmol/mg. The affinities of the M2 subtype-selective muscarinic antagonists methoctramine and AF-DX 116 were similar in both membrane preparations. The receptor population associated with the deep muscular plexus synaptosomal fraction was linked to the inhibition of adenylate cyclase activity, as demonstrated by a concentration-dependent, atropine-sensitive inhibition of the forskolin-stimulated enzyme in the presence of muscarinic agonists carbachol and oxotremorine. Based on the pharmacological observations presented here, the prejunctional muscarinic receptors in the axonal varicosities of deep muscular plexus are different from the postjunctional receptors present in the circular smooth muscle.

Adenylyl Cyclases↗
PubMed1979

Guanidoacetate methyltransferase. Purification and molecular properties.

Guanidoacetate methyltransferase has been purified about 140-fold from pig liver. Polyacrylamide gel electrophoresis of the purified enzyme showed four protein bands, each of which is associated with guanidoacetate methyltransferase activity. During gel electrophoresis at pH 3 in 8 M urea, guanidoacetate methyltransferase migrated as a single component. The molecular weight of the purified guanidoacetate methyltransferase was estimated to be 31,000 by sodium dodecyl sulfate-gel electrophoresis, which also showed only one protein component with guanidoacetate methyltransferase activity. This molecular weight is in agreement with that estimated by Sephadex G-75 chromatography. Guanidoacetate methyltransferase is inhibited by adenosylhomocysteine, 3-deazaadenosylhomocysteine, and sinefungin with Ki values of 16 microM, 39 microM, and 18 microM, respectively.

Amino Acids↗
PubMed1978

Adenosylhomocysteine hydrolase. Crystallization of the purified enzyme and its properties.

Adenosylhomocysteine hydrolase (EC 3.3.1.1) from calf liver was purified to homogeneity by crystallization. The purified enzyme exhibited one single component in polyacrylamide gel electrophoresis. But by Ampholine gel electrophoresis, two isoelectric focusing variants were observed, with pI values at 5.8 and 6.0. when subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, one major subunit with a molecular weight of 60,000 was found; five other minor subunit variants were also observed, with molecular weights ranging between 50,000 and 57,000. These minor subunit variants comprised approximately 15% of the total protein applied. The molecular weight of the native enzyme was estimated to be 237,500 by gradient gel electrophoresis. The native enzyme is probably composed of four subunits, each with a molecular weight of not more than 60,000. Amino acid analyses of the purified enzyme revealed the presence of 1.2 residues of glucosamine/mol of enzyme, in addition to all of the common amino acids. The presence of enzyme-bound NAD was confirmed, probably 1 NAD molecule bound/enzyme subunit. In addition to adenosine, 3-deazaadenosine was found to be an effective substrate as well in the direction of synthesis.

Amino Acids↗
PubMed1977

Glycogen metabolism in the snail, Biomphalaria glabrata.

1. The distribution of glycogen in different tissues of the snail, Biomphalaria glabrata was determined; the cephalopedal region contained 15-17 mg, the mantle region 23-29 mg, the hepatopancreas 31-45 mg, and the ovotestis 50 mg of glycogen/g wet wt. 2. There was a significant decrease in the glycogen content in the cephalopedal region after incubating the snails with 5-hydroxytryptamine (4 x 10(-5) M) in vivo. 3. Enzymatic degradation of glycogen from different tissues revealed that the degree of branching was 9% of the total glucosyl residues, and the length of outer branches was about 40% of the total glucosyl residues. 4. There was an active form of glycogen phosphorylase in the cephalopedal region and the mantle region. Phosphorylase in the hepatopancreas was generally inactive, but could be activated by an endogenous phosphorylase kinase. 5. Glycogen synthetase of the snail tissues required glucose-6-phosphate to be active.

Animals↗
PubMed1975

Control of pyruvate dehydrogenase activity in intact cardiac mitochondria. Regulation of the inactivation and activation of the dehydrogenase.

The control of pyruvate dehydrogenase activity by inactivation and activation was studied in intact mitochondria isolated from rabbit heart. Pyruvate dehydrogenase could be completely inactivated by incubating mitochondria with ATP, oligomycin, and NaF. This loss in dehydrogenase activity was correlated with the incorporation of 32P from [gamma-32P]ATP into mitochondrial protein(s) and with a decrease in the mitochondrial oxidation of pyruvate. ATP may be supplied exogenously, generated from endogenous ADP during oxidative phosphorylation, or formed from exogenous ADP in carbonyl cyanid p-trifluoromethoxyphenylhydrazone-uncoupled mitochondria. With coupled mitochondria the concentration of added ATP required to half-inactivate the dehydrogenase was 0.24 mM. With uncoupled mitochondria the apparent Km was decreased to 60 muM ATP. Inactivation of pyruvate dehydrogenase by exogenous ATP was sensitive to atractyloside, suggesting that pyruvate dehydrogenase kinase acts internally to the atractyloside-sensitive barrier. The divalent cation ionophore, A23187, enhanced the loss of dehydrogenase activity. Pyruvate dehydrogenase activity is regulated additionally by pyruvate, inorganic phosphate, and ADP. Pyruvate, in the presence of rotenone, strongly inhibited inactivation. This suggests that pyruvate facilitates its own oxidation and that increases in pyruvate dehydrogenase activity by substrate may provide a modulating influence on the utilization of pyruvate via the tricarboxylate cycle. Inorganic phosphate protected the dehydrogenase from inactivation by ATP. ADP added to the incubation mixture together with ATP inhibited the inactivation of pyruvate dehydrogenase. This protection may result from a direct action on pyruvate dehydrogenase kinase, as ADP competes with ATP, and an indirect action, in that ADP competes with ATP for the translocase. It is suggested that the intramitochondrial [ATP]:[ADP] ratio effects the kinase activity directly, whereas the cytosolic [ATP]:[ADP] ratio acts indirectly. Mg2+ enhances the rate of reactivation of the inactivated pyruvate dehydrogenase presumably by accelerating the rate of dephosphorylation of the enzyme. Maximal activation is obtained with the addition of 0.5 mM Mg2+..

Adenosine Diphosphate↗