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Biomedical subjects

H Will

Publications and source records attributed to H Will.

At least 235 records · Page 13Linked to original sources
PubMed1978

Partial characterization of protein kinase-catalyzed phosphorylation of low molecular weight proteins in purified preparations of pigeon heart sarcolemma and sarcoplasmic reticulum.

Pigeon heart microsomes contain three minor size protein kinase substrates of minimal molecular weights of 22 000, 15 000, and 11500, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When the microsomes were partially loaded with calcium oxalate and subjected to rate zonal and isopycnic centrifugations in sucrose density gradient columns, the 22 000 and the 15 000 dalton proteins settled in the heaviest fraction, which was composed mainly of vesicles of sarcoplasmic reticular membranes; the 11 500 dalton protein was concentrated in the lightest fractions, which consisted chiefly of vesicles of sarcolemmal origin. During incubation of the membrane fractions with Mg [gamma-32P]ATP significant amounts of 32P were incorporated into all these proteins. Incorporation of 32P into the 15 000 dalton protein was moderately and 32P incorporation into the 22 000 dalton protein was markedly enhanced in the presence of exogenous soluble cyclic AMP-dependent protein kinase and cyclic AMP. The phosphorylation of the three proteins was virtually unaffected by Ca2+ concentrations up to 0.1 mM and by ethyleneglycol-bis-(beta-aminoethyl-ether)-N,N'-tetraacetic acid in the absence of added Ca2+. Phosphorylation of the 22 000 and the 11 500 dalton proteins occurred mainly at serine residues. In the 15 000 dalton protein threonine residues were the main site of endogenous phosphorylation. Nearly equal amounts of [32P]-phosphate were incorporated into threonine and serine residues of this protein, when phosphorylation was supported by exogenous cyclic AMP-dependent protein kinase and cyclic AMP. The 15 000 dalton protein could be removed from its membrane attachment by extraction with an acidic chloroform/methanol mixture. This step opens the way for the purification of this membrane-bound protein kinase substrate.

Animals↗
PubMed1976

A quench-flow kinetic investigation of calcium ion accumulation by isolated cardiac sarcoplasmic reticulum. Dependence of initial velocity on free calcium ion concentration and influence of preincubation with a protein kinase, MgATP, and cyclic AMP.

Ca2+ accumulation at pH 6.8 by isolated rabbit heart microsomes derived chiefly from sarcoplasmic reticulum was investigated by a quench-flow technique. The reaction was terminated at preset times by addition to the reaction mixture of an equal volume of 10 to 50 mM ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid buffered at pH 6.0. The initial velocity of Ca2+ accumulation by microsomal preparations exhibiting a steady state Ca2+ accumulation of 25.6 nmol Ca2+/mg increased from 3.67 to 33.4 nmol Ca2+/mg - s as the free Ca2+ concentration was raised from 0.2 to 18.9 muM. Preincubation of the cardiac microsomes with a partly purified soluble cardiac cyclic AMP-dependent protein kinase, MgATP, and cyclic AMP lead to a significant increase in the initial Ca2+ accumulation rate. The amounts of Ca2+ that were found to accumulate in the first 200 ms of the reaction are comparable to the quantities of the ion that according to literature data need to be removed from the myofilaments and the myoplasm for induction of relaxation of the myocardial fibers.

Adenosine Triphosphate↗
PubMed1976

Increased Ca2+ binding by a cardiac cell membrane preparation after cyclic AMP-enhanced intrinsic membrane protein phosphorylation.

Ca2+ binding to a sarcolemma-enriched membrane fraction from pig myocardium possessing an intrinsic cyclic AMP-dependent protein kinase occurs at several classes of low affinity binding sites and at two high affinity binding sites with binding constants of about 1.5-1.7x10(7) M-1 (0.3 nmole of Ca2+/mg protein) and 0.9-2.9x10(6) M-1 (0.8 nmole of Ca2+/mg protein). Ca2+ binding properties are not affected by verapamil and ouabain, whereas ruthenium red depresses Ca2+ binding at the low affinity binding sites and La3+ ions strongly reduce both low and high affinity Ca2+ binding. A profound inhibition of the high affinity Ca2+ binding sites was observed in the presence of Na+ ions, half-maximal inhibition at a free Ca2+ concentration of 2x10(-8) M being achieved by 11 mM NaC1. High affinity Ca2+ binding is also diminished after pretreatment of the membranes with trypsin and phospholipase A. Phosphorylation of one or two of the membrane proteins by the endogenous cyclic AMP-dependent protein kinase leads at both classes of high affinity Ca2+ binding sites to an approximately 4-fold increase in affinity, the number of these sites remaining unchanged. The high affinity Ca2+ binding sites may possibly be involved in Ca2+ extrusion from the cell and in the relaxation process.

Animals↗
PubMed1976

Stimulation of Ca2+ uptake by cyclic AMP and protein kinase in sarcoplasmic reticulum-rich and sarcolemma-rich microsomal fractions from rabbit heart.

The effect of cyclic AMP on Ca2+ uptake by rabbit heart microsomal vesicular fractions representing mainly fragments of either sarcoplasmic reticulum or sarcolemma was investigated in the presence and absence of soluble cardiac protein kinase and with microsomes prephosphorylated by cyclic AMP-dependent protein kinase. The acceleration of oxalate-promoted Ca2+ uptake by fragmented sarcoplasmic reticulum following cyclic AMP-dependent membrane protein phosphorylation, observed by other authors, was confirmed. In addition it was found that the acceleration was greatest at pH 7.2 and almost negligible at pH 6.0 and pH 7.8. A very marked increase in Ca2+ uptake by cyclic AMP-dependent membrane protein phosphorylation was observed in the presence of boric acid, a reversible inhibitor of Ca2+ uptake. In addition to the microsomal fraction thought to represent mainly fragments of the sarcoplasmic reticulum, the effect of protein kinase and cyclic AMP on Ca2+ uptake was investigated in a cardiac sarcolemma-enriched membrane fraction. Ca2+ uptake by sarcolemmal vesicles, unlike Ca2+ uptake by sarcoplasmic reticulum vesicles, was inhibited by low doses of digitoxin. The acceleration of oxalate-promoted Ca2+ uptake by cyclic AMP and soluble cardiac protein kinase, however, was quite similar to what was seen in preparations of fragmented sarcoplasmic reticulum, which suggests that it may reflect an acceleration of active Ca2+ transport across the myocardial cell surface membrane.

Animals↗
PubMed1975

The assay of glycogen phosphorylase in human blood serum and its application to the diagnosis of myocardial infarction.

Methods are described (a) for the estimation of glycogen phosphorylase activity (EC 2.4.1.1) in human blood serum based on the chemical determination of liberated orthophosphate or on the enzymic determination of glucose 1-phosphate in a coupled assay system and (b) for the electrophoretic separation of isophosphorylases I, II, and III in human. Glycogen phosphorylase activities ranging from 1.5 to 18 mU/ml were found in the serum of patients with acute myocardial infarction. In contrast, no glycogen phosphorylase activity was detected in the serum of healthy persons. The enzyme appears in the serum 4 hours after the onset of the infarction and reaches a maximum after 20 to 30 hours. Acrylamide gel electrophoresis of serum after a myocardial infarction revealed only muscle isophosphorylase I, the isoenzyme characteristic of the heart. No phosphorylase activity was detected in serum of patients with angina pectoris, endocarditis, and uncomplicative congestive heart failure. From these findings it appears that the new serum enzyme test may prove to be a valuable addition to presently existing methods for the early differential diagnosis of acute myocardial infarction.

Clinical Enzyme Tests↗
PubMed1975

Adenosine 3',5'-monophosphate, the myocardial cell membrane, and calcium.

Catecholamine-sensitive adenylate cyclase, cyclic nucleotide phosphodiesterase, adenosine 3', 5'-monophosphate (cyclic AMP)-dependent protein kinase, kinase substrate, and phosphoprotein phosphatase have variously been reported to be present in preparations of myocardial cellular membranes that function in the movement of Ca2+ in and out of the cell and in intracellular Ca2+ translocations, indicating that these membranees possess the equipment for the formation and destruction of cyclic Amp as well as for the initiation, effectuation, and termination of a possible membrane action of the nucleotide. It has also been observed that phosphorylation of seryl residues of protein in sarcolemma- and sarcotubule-rich myocardial subcellular fractions by cyclic AMP activated intrinsic and extrinsic protein kinases confers upon these membran structures an enhanced ability to bind or take up Ca2+ and that dibutyryl cyclic AMP, like adrenaline, produces in intact cardiac muscle simultaneous increases in contractile force and in the uptake of extracellular Ca2+. These findings are suggestive of a second messenger role of cyclic AMP in the beta-adrenoreceptor-mediated actions of catecholamines on myocardial contractile force and relaxation, in which Ca2+ would serve as a third messenger and be subject, respectively, to more effective removal from its binding sites on troponin. An alternative interpretation regards Ca2+ and cyclic AMP as interdependent twin second messengers in the catecholamine-induced inotropism. Since the physiological meaning of the reported effects of cyclic AMP on isolated myocardial membrane preparations is far from established an instances of a dissociation between the effects of catecholamines on myocardial contractile force and cyclic AMP levels have been observed, there is still room for hypotheses that relegate cyclic AMP to a nonobligatory, at most, supportive role in the action of the catecholamines on cardiac contraction.

Animals↗