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Biomedical subjects

M Weller

Publications and source records attributed to M Weller.

At least 343 records · Page 19Linked to original sources
PubMed1981

GTP, as well as ATP, can act as a substrate for the intrinsic protein kinase activity of synaptic plasma membranes.

GTP as well as ATP can act as phosphate donor for the intrinsic protein kinase activity of synaptic plasma membranes. There are many similarities between the activities observed with ATP or GTP. Both need a divalent cation, Mg2+ being preferred, both are slightly inhibited by Na+, and more strongly by K+, both are inhibited by theophylline and adenosine. The Km for GTP (0.13 mM) is similar to that ATP (0.12 mM). There are, however, some differences in properties. When GTP instead of ATP is the phosphate donor the pH optimum is 6.5 instead of 7.4. In addition NH4+ inhibits the transfer of phosphate from GTP but not from ATP. More importantly, cyclic AMP only stimulates the transfer of phosphate from ATP not from GTP. SDS gel electrophoresis reveals that similar membrane proteins are phosphorylated by GTP and ATP in the presence or absence of cyclic AMP. This suggests that there may be two different types of protein kinase in the synaptic plasma membrane which act on similar membrane proteins. One is stimulated by cyclic AMP and is specific to ATP while the other is unaffected by cyclic nucleotides and can use either ATP or GTP as phosphate donor.

Adenosine Triphosphate↗
PubMed1981

The soluble, cyclic AMP-stimulated protein kinase catalyses the phosphorylation of different membrane proteins from those which are phosphorylated by the membrane bound enzyme.

Soluble, cyclic AMP stimulated protein kinase (type a1 protein kinase) stimulated the phosphorylation of membrane proteins in preparations from a wide variety of tissues. This kinase does not, however, appear to catalyse the phosphorylation of the same membrane proteins which are phosphorylated by the intrinsic protein kinase activity of the preparations. This was demonstrated in two ways: 1. If preparations of membrane fragments are incubated with [gamma 32P] ATP in the absence of type a1 protein kinase, until all membrane bound protein acceptor sites are saturated with phosphate addition of type a1 protein kinase causes the incorporation of more phosphate into the membrane proteins. 2. The nature of the membrane proteins phosphorylated by type a1 protein kinase and the intrinsic protein kinase of the preparation was compared by SDS gel electrophoresis. Membrane preparations were phosphorylated with [gamma 32P] ATP in the absence of added type a1 protein kinase and with [gamma 33P] ATP in the presence of the enzyme. Aliquots of the two samples were then mixed, separated by SDS gel electrophoresis, and the distribution of radioactivity measured. A comparison of the distribution of protein bound 33P and 32P made it quite clear that type a1 protein kinase catalysed the phosphorylation of different membrane proteins from those which are phosphorylated by the intrinsic protein kinase activity of the preparations.

Animals↗
PubMed1981

Effect of propranolol and phenothiazines on electrodermal orienting and habituation in schizophrenia.

Bilateral electrodermal orienting responses were measured to repeated auditory stimuli in schizophrenic patients and controls. In 3 studies phasic activity to moderate intensity sounds of patients on no drugs or phenothiazines was predominantly hyper- or hypo-responsive. Controls showed moderate or slow habituation. Propranolol was found to facilitate habituation in slow habituators and to reinstate responses in half of non-responders, especially when given as the sole drug. The effects seldom had a counterpart in changes in non-specific responses or levels of skin conductance. Modulatory influences on stimulus and response processing and on lateral asymmetries in responses may underlie propranolol's efficacy in treating schizophrenia.

Acoustic Stimulation↗
PubMed1979

The time course of the phosphorylation of proteins in the synaptic plasma membrane and the effect of certain cations.

The phosphorylation of proteins in the synaptic plasma membrane is a rather slow reaction taking several minutes to saturate all the phosphate acceptor sites. (The time for half the protein bound phosphate groups to turnover is about 1 min). A divalent cation is needed as a cofactor for the reaction. At high (0.5 mM) ATP concentrations Mg2+ is more effective than Mn2+ but at low (10 microM) ATP concentrations the reverse is the case. Zn2+ and Ca2+ support very little phosphorylation.

Adenosine Triphosphate↗
PubMed1979

The effect of cyclic nucleotides and protein phosphorylation on calcium permeability and binding in the sarcoplasmic reticulum.

In the absence of cyclic nucleotides heart microsomes have two classes of calcium binding sites with binding constants of 0.69 and 0.071 micron-1 and capacities of 2.2 and 9.7 nmol/mg protein, respectively. Neither cyclic AMP nor monobutyryl cyclic AMP affect binding but cyclic GMP and monobutyryl cyclic GMP cause the complete loss of the high affinity calcium binding sites, Cyclic GMP (but not monobutyryl cyclic GMP) also causes a decrease in the binding constant of the low affinity binding sites. AMP, GMP and Tris-butyrate do not affect calcium binding. The effects of the cyclic nucleotides are direct and are not mediated by protein phosphorylation. Phosphorylation of microsomal proteins increases the binding constant but not the capacity of the high affinity calcium binding sites. The capacity and also, perhaps, binding constant of the low affinity sites is also increased by phosphorylation. In additon to their effects on calcium binding the cyclic nucleotides also affect the movements of calcium into and out of the microsomes. The effects are again direct and not mediated by protein phosphorylation. Cyclic GMP decreases the rate of Ca2+ efflux from preloaded cardiac microsomes and also appears to decrease the rate of uptake of Ca2+ by cardiac microsomes though this effect is less clear cut than the action on efflux. The cyclic nucleotide has a half maximal effect at a concentration of 100 microns. By contrast cyclic AMP increases the rate of influx of Ca2+ into heart microsomes and the rate of efflux of Ca2+ from preloaded preparations. The effect is, however, rather slight. It is suggested that the most obvious interpretation of these results is that cyclic GMP decreases the Ca2+ permeability of the cardiac microsomal membrane while cyclic AMP increases the permeability. In contrast to the results found with membrane preparations from certain other tissues phosphorylation of cardiac microsomal proteins does not appear to alter Ca2+ efflux or influx out of, or into, cardiac microsomal preparations. It is thus concluded that phosphorylation of cardiac microsomal proteins does not affect the Ca2+ permeability of the microsomal membrane.

Animals↗
PubMed1979

A comparison of the intrinsic protein kinase activities of membrane preparations from various tissues.

The ability of membrane preparations from different tissues to catalyse the phosphorylation of their endogenous protein (intrinsic protein kinase activity) was determined. It was found that membrane fragments prepared from a large variety of tissues contain this activity although the actual level varies quite widely. Preparations from vas deferens and brain have nearly ten times more activity than preparations from heart, kidney, or erythrocytes. Plasma membranes from skeletal muscle have no detectable activity. The intrinsic protein kinase activity of membrane fragments from most tissues is stimulated by cyclic AMP although the phosphorylation of proteins in preparations of kidney microsomes or heart plasma membranes, is not affected. cyclic GMP (10 micronM) has no effect on the intrinsic protein kinase activity of any membrane preparation examined. A specific inhibitor of soluble, cyclic AMP-stimulated, protein kinase has no effect on the intrinsic protein kinase activity of any of the membrane preparations examined. This suggests that the intrinsic protein kinase activity of membrane preparations may be due to the presence of a specific protein kinase. It is suggested that an examination of the distribution of membrane-bound intrinsic protein kinase activity among different tissues may be helpful in determining the function of the reaction.

Animals↗
PubMed1979

Influence of D-or DL-propranolol and chlorpromazine on habituation of phasic electrodermal responses in schizophrenia.

Propranolol was found to share the properties of the racemate in facilitating habituation of the electrodermal orienting reflex in schizophrenic patients. This effect appeared independent of influences on levels of skin conductance and non-specific responses. Chlorpromazine did not normalise orienting activity. If the findings from open clinical studies that D-propranolol has anti-psychotic properties are confirmed, the fact that dextro propranolol has only minimal cardiovascular effects may give it important advantages as an anti-psychotic agent. Controlled clinical studies to prove its therapeutic action and neurobiological studies to determine its central mechanisms of action are warranted.

Adolescent↗
PubMed1978

The effect of cyclic nucleotides and protein phosphorylation on the permeability of human erythrocyte ghosts to certain cations.

Preparations of human erythrocyte membranes have been made which are in the form of sealed vesicles and which behave as osmometers on suspension in solutions of simple inorganic salts. Using these preparations the permeability of the membranes to Na+, K+, Mg2+ and Ca2+ was measured. Cyclic AMP (but not cyclic GMP) increased the permeability of the membranes to Ca2+ with a half maximal effect at a concentration of 25 microgram but did not affect the permeability to the other ions tested. Phosphorylation of proteins in the erthrocyte membrane lowered the permeability to Ca2+ without affecting the permeability to the other ions tested and there was a good correlation between the time course of protein phosphorylation and decrease in Ca2+ permeability. It is postulated that the system through which cyclic AMP causes an initial rapid rise in Ca2+ permeability followed by increased phosphorylation of membrane proteins and reduced Ca2+ permeability may have a widespread occurrence in biological systems and serve to control the concentration of Ca2+ in the cytoplasm.

Calcium↗
PubMed1978

Cyclic AMP increase the Na+ permeability of the avian erythrocyte membrane by a process which does not involve protein phosphorylation.

Preparations of avian erythrocyte plasma membranes have been made which are in the form of sealed vesicles. Using these preparations the permeability of the membranes to N+, K+, Mg2+ and Ca2+ was measured. Monobutyryl cyclic AMP and cyclic AMP increased the permeability to Na+ and Ca+ under conditions where no protein phosphorylation could occur. The only effect of phosphorylation of membrane proteins was to reduce Ca+ permeability. It is thus concluded that cyclic AMP increases Na+ permeability in the avian erythroycte by a direct effect which does not involve protein phosphorylation.

Animals↗
PubMed1978

Protein-bound histidine, as well as protein-bound serine, residues are sites of phosphorylation in the synaptic plasma membrane.

When synaptic plasma membrane fragments are incubated with ATP in the presence of Mg2+, phosphate is transferred, not only to protein-bound serine, but also to protein-bound histidine. The phosphorylation of protein-bound serine is stimulated by cyclic AMP and has a Km for ATP of about 0.12 mM, both in the presence and absence of cyclic AMP. By contrast, the phosphorylation of protein-bound histidine is unaffected by cyclic AMP and does not follow Michaelis-Menton kinetics since a non-linear double reciprocal plot is given when activity is measured at various ATP concentrations.

Adenosine Triphosphate↗
PubMed1977

A possible role of the phosphorylation of synaptic membrane proteins in the control of calcium ion permeability.

Incubation of synaptosomes under conditions which result in complete phosphorylation of membrane bound accepter proteins does not affect the permeability to Na+ or K+ as measured by a spectrophotometric method. This technique was not, however, sensitive enough to determine permeability to Ca2+ which was thus estimated, using 45Ca2+. It was found that although phosphorylation did not affect the equilibrium binding of 45Ca it did lower the rate of both Ca2+ uptake and efflux. The most likely interpretation of these results is that phosphorylation of proteins in the synaptic membrane lowers the permeability of the membrane to Ca2+. This could have a role in the regulation of synaptic transmission.

Animals↗
PubMed1976

Distribution of protein kinase activities in subcellular fractions of rat brain.

The subcellular distribution of histone and phosvitin kinase activities in brain has been studied and the ability of the various fractions to catalyse the phosphorylation of their endogenous proteins (intrinsic protein kinase activity) also examined. Synaptosome membrane fragments have little or no histone or phosvitin kinase activity but contain the highest concentration of cyclic AMP-stimulated intrinsic protein kinase activity. Homogenisation of the membrane fragments in Triton X-100 increased the histone kinase activity but on centrifugation it was all recovered in the supernatant, while the insoluble material contained all the intrinsic protein kinase activity. These results indicate that the intrinsic protein kinase activity of cerebral membrane fragments is due to the presence of a kinase enzyme which is specific to certain membrane proteins. The intrinsic protein kinase activity of synaptosome membrane fragments is a rather slow reaction which takes several minutes to saturate all the acceptor proteins.

Animals↗