Biography:

In the past Norbert I. Swislocki has collaborated on articles with Marian B. Meyers and Earlene Brown Cunningham. One of their most recent publications is Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism☆. Which was published in journal Archives of Biochemistry and Biophysics.

More information about Norbert I. Swislocki research including statistics on their citations can be found on their Copernicus Academic profile page.

Norbert I. Swislocki's Articles: (12)

Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism☆

AbstractMembranes were prepared from fresh, washed human erythrocytes by hemolysis and washing with 5 mm sodium phosphate buffer (pH 7.4). The mean residue ellipticity, [θ], of erythrocyte membrane circular dichroism was altered by prostaglandin E1 or prostaglandin F2α at 37 °C when observed from 250 nm to 190 nm. The decrease in negativity of [θ] with 10−6m prostaglandin E1 was 12.7% at 222 nm and 17.7% at 208 nm, and with 10−6m prostaglandin F2α 22.5% and 34.2%, respectively (P < 0.01). Similar changes in [θ] were observed at lower concentrations of prostaglandins. No strict relationship between amount of change of [θ] and prostaglandin concentrations of 3 × 10−5m to 3 × 10−12m was evident. A persistent alteration of [θ] with prostaglandin was observed at 37 °C. Transient change of [θ] occurred at 25 °C with prostaglandin. No change of [θ] was observed at 15 or 20 °C. Buffer or palmitic acid were without effect on membrane [θ]. Phosphatidyl inositol or methyl arachidonate caused an increase in negativity of membrane spectra. The observed alterations of membrane [θ] did not arise from changes in light scattering as the OD700–OD200 of membranes was not changed by prostaglandin. Effects of prostaglandin were not dependent on light path length. The prostaglandin E1 antagonist, 7-oxa-13-prostynoic acid, at 10−7m produced no change of [θ] of membrane spectra and prevented the otherwise demonstrable effects of 10−10m prostaglandin E1 on [θ]. The decrease in negativity of [θ] at 222 nm is indicative of a decrease in ellipticity of membrane protein. These studies suggest that prostaglandins may act by inducing a conformational change in membrane protein.

Activation of solubilized liver membrane adenylate cyclase by guanyl nucleotides☆

AbstractLiver plasma membranes of hypophysectomized rats were purified, treated with 0.1 m Lubrol-PX and centrifuged at 165,000g for 1 h. The detergent solubilized 50% of the membrane protein; adenylate cyclase activity was present in the supernatant fraction. Optimal substrate concentration of the soluble enzyme was 0.32 mm ATP. Basal activity of 25 preparations of the solubilized enzyme ranged from 124 to 39 pmol cyclic AMP/mg protein/10 min. The solubilized enzyme retained the same sensitivity to activation by guanyl nucleotides as was present in the membrane preparation from which it was derived. Relative sensitivity of the solubilized enzyme with 0.1 mm nucleotides or -side was GDP > GTP > GMP > guanosine; GMP-PNP = GMP-PCP > ITP > GTP. GTP, GMP-PCP, GMP-PNP and other nucleotides were hydrolyzed by phosphohydrolases present in liver membranes that were solubilized with Lubrol-PX along with adenylate cyclase. The presence of the ATP regenerating system in the adenylate cyclase assay also aided in maintaining guanyl nucleotide concentrations. The degree of adenylate cyclase activation by guanyl nucleotides was not related to the sparing effects of nucleotides on substrate ATP hydrolysis. These findings demonstrate that activation of adenylate cyclase by nucleotides is a consequence of a nucleotide-enzyme interaction that is independent of membrane integrity.

BBA reportModulation of the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte

AbstractWe previously reported that the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte membrane is inhibited by micromolar or nanomolar concentrations of cyclic AMP. Our further studies have now indicated that the inhibition of (Ca2+ + Mg2+)-dependent phosphohydrolase activity requires the participation of a membrane-associated cyclic AMP-dependent protein kinase and a membrane-associated protein substrate that is distinct from the ATPase itself. We have furthermore, identified a 20 kDa membrane protein which undergoes phosphorylation that is promoted by micromolar, but not millimolar, concentrations of cyclic AMP and which, when phosphorylated, undergoes dephosphorylation that is promoted by Ca2+. We suggest that this membrane component can participate in the modulation of the activity of the (Ca2+ + Mg2+)-dependent ATPase of the human erythrocyte.

Activation of solubilized liver membrane adenylate cyclase by nucleotides

AbstractLiver plasma membranes isolated from hypophysectomized rats were treated with 0.1 M Lubrol-PX, a nonionic detergent, and centrifuged at 165,000 × g for 1 hour. Adenylate cyclase activity remaining in the supernate had a specific activity that was at least equal to that of the particulate enzyme. The activity of the solubilized, non-sedimentable adenylate cyclase, as well as the membrane bound enzyme, was increased by GTP, ITP, and GMP-PCP at 10−4 M. The activity of the solubilized, non-sedimentable enzyme increased linearly with GTP from 10−6 to 10−4 M but there was no further increase in the activity of the solubilized enzyme with 10−3 M GTP. In contrast, the particulate liver membrane enzyme activity increased exponentially with GTP from 10−6 to 10−4 M and was further increased by 10−3 M GTP. These data indicate that GTP, ITP or GMP-PCP have direct effects on solubilized adenylate cyclase. This effect is in addition to a role of nucleotides in modifying membrane structure (16).

Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism☆

AbstractMembranes were prepared from fresh, washed human erythrocytes by hemolysis and washing with 5 mm sodium phosphate buffer (pH 7.4). The mean residue ellipticity, [θ], of erythrocyte membrane circular dichroism was altered by prostaglandin E1 or prostaglandin F2α at 37 °C when observed from 250 nm to 190 nm. The decrease in negativity of [θ] with 10−6m prostaglandin E1 was 12.7% at 222 nm and 17.7% at 208 nm, and with 10−6m prostaglandin F2α 22.5% and 34.2%, respectively (P < 0.01). Similar changes in [θ] were observed at lower concentrations of prostaglandins. No strict relationship between amount of change of [θ] and prostaglandin concentrations of 3 × 10−5m to 3 × 10−12m was evident. A persistent alteration of [θ] with prostaglandin was observed at 37 °C. Transient change of [θ] occurred at 25 °C with prostaglandin. No change of [θ] was observed at 15 or 20 °C. Buffer or palmitic acid were without effect on membrane [θ]. Phosphatidyl inositol or methyl arachidonate caused an increase in negativity of membrane spectra. The observed alterations of membrane [θ] did not arise from changes in light scattering as the OD700–OD200 of membranes was not changed by prostaglandin. Effects of prostaglandin were not dependent on light path length. The prostaglandin E1 antagonist, 7-oxa-13-prostynoic acid, at 10−7m produced no change of [θ] of membrane spectra and prevented the otherwise demonstrable effects of 10−10m prostaglandin E1 on [θ]. The decrease in negativity of [θ] at 222 nm is indicative of a decrease in ellipticity of membrane protein. These studies suggest that prostaglandins may act by inducing a conformational change in membrane protein.

Activation of solubilized liver membrane adenylate cyclase by guanyl nucleotides☆

AbstractLiver plasma membranes of hypophysectomized rats were purified, treated with 0.1 m Lubrol-PX and centrifuged at 165,000g for 1 h. The detergent solubilized 50% of the membrane protein; adenylate cyclase activity was present in the supernatant fraction. Optimal substrate concentration of the soluble enzyme was 0.32 mm ATP. Basal activity of 25 preparations of the solubilized enzyme ranged from 124 to 39 pmol cyclic AMP/mg protein/10 min. The solubilized enzyme retained the same sensitivity to activation by guanyl nucleotides as was present in the membrane preparation from which it was derived. Relative sensitivity of the solubilized enzyme with 0.1 mm nucleotides or -side was GDP > GTP > GMP > guanosine; GMP-PNP = GMP-PCP > ITP > GTP. GTP, GMP-PCP, GMP-PNP and other nucleotides were hydrolyzed by phosphohydrolases present in liver membranes that were solubilized with Lubrol-PX along with adenylate cyclase. The presence of the ATP regenerating system in the adenylate cyclase assay also aided in maintaining guanyl nucleotide concentrations. The degree of adenylate cyclase activation by guanyl nucleotides was not related to the sparing effects of nucleotides on substrate ATP hydrolysis. These findings demonstrate that activation of adenylate cyclase by nucleotides is a consequence of a nucleotide-enzyme interaction that is independent of membrane integrity.

BBA reportModulation of the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte

AbstractWe previously reported that the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte membrane is inhibited by micromolar or nanomolar concentrations of cyclic AMP. Our further studies have now indicated that the inhibition of (Ca2+ + Mg2+)-dependent phosphohydrolase activity requires the participation of a membrane-associated cyclic AMP-dependent protein kinase and a membrane-associated protein substrate that is distinct from the ATPase itself. We have furthermore, identified a 20 kDa membrane protein which undergoes phosphorylation that is promoted by micromolar, but not millimolar, concentrations of cyclic AMP and which, when phosphorylated, undergoes dephosphorylation that is promoted by Ca2+. We suggest that this membrane component can participate in the modulation of the activity of the (Ca2+ + Mg2+)-dependent ATPase of the human erythrocyte.

Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism☆

AbstractMembranes were prepared from fresh, washed human erythrocytes by hemolysis and washing with 5 mm sodium phosphate buffer (pH 7.4). The mean residue ellipticity, [θ], of erythrocyte membrane circular dichroism was altered by prostaglandin E1 or prostaglandin F2α at 37 °C when observed from 250 nm to 190 nm. The decrease in negativity of [θ] with 10−6m prostaglandin E1 was 12.7% at 222 nm and 17.7% at 208 nm, and with 10−6m prostaglandin F2α 22.5% and 34.2%, respectively (P < 0.01). Similar changes in [θ] were observed at lower concentrations of prostaglandins. No strict relationship between amount of change of [θ] and prostaglandin concentrations of 3 × 10−5m to 3 × 10−12m was evident. A persistent alteration of [θ] with prostaglandin was observed at 37 °C. Transient change of [θ] occurred at 25 °C with prostaglandin. No change of [θ] was observed at 15 or 20 °C. Buffer or palmitic acid were without effect on membrane [θ]. Phosphatidyl inositol or methyl arachidonate caused an increase in negativity of membrane spectra. The observed alterations of membrane [θ] did not arise from changes in light scattering as the OD700–OD200 of membranes was not changed by prostaglandin. Effects of prostaglandin were not dependent on light path length. The prostaglandin E1 antagonist, 7-oxa-13-prostynoic acid, at 10−7m produced no change of [θ] of membrane spectra and prevented the otherwise demonstrable effects of 10−10m prostaglandin E1 on [θ]. The decrease in negativity of [θ] at 222 nm is indicative of a decrease in ellipticity of membrane protein. These studies suggest that prostaglandins may act by inducing a conformational change in membrane protein.

Activation of solubilized liver membrane adenylate cyclase by guanyl nucleotides☆

AbstractLiver plasma membranes of hypophysectomized rats were purified, treated with 0.1 m Lubrol-PX and centrifuged at 165,000g for 1 h. The detergent solubilized 50% of the membrane protein; adenylate cyclase activity was present in the supernatant fraction. Optimal substrate concentration of the soluble enzyme was 0.32 mm ATP. Basal activity of 25 preparations of the solubilized enzyme ranged from 124 to 39 pmol cyclic AMP/mg protein/10 min. The solubilized enzyme retained the same sensitivity to activation by guanyl nucleotides as was present in the membrane preparation from which it was derived. Relative sensitivity of the solubilized enzyme with 0.1 mm nucleotides or -side was GDP > GTP > GMP > guanosine; GMP-PNP = GMP-PCP > ITP > GTP. GTP, GMP-PCP, GMP-PNP and other nucleotides were hydrolyzed by phosphohydrolases present in liver membranes that were solubilized with Lubrol-PX along with adenylate cyclase. The presence of the ATP regenerating system in the adenylate cyclase assay also aided in maintaining guanyl nucleotide concentrations. The degree of adenylate cyclase activation by guanyl nucleotides was not related to the sparing effects of nucleotides on substrate ATP hydrolysis. These findings demonstrate that activation of adenylate cyclase by nucleotides is a consequence of a nucleotide-enzyme interaction that is independent of membrane integrity.

BBA reportModulation of the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase of the human erythrocyte

AbstractWe previously reported that the activity of the (Ca2+ + Mg2+)-dependent adenosine triphosphatase (ATPase) of the human erythrocyte membrane is inhibited by micromolar or nanomolar concentrations of cyclic AMP. Our further studies have now indicated that the inhibition of (Ca2+ + Mg2+)-dependent phosphohydrolase activity requires the participation of a membrane-associated cyclic AMP-dependent protein kinase and a membrane-associated protein substrate that is distinct from the ATPase itself. We have furthermore, identified a 20 kDa membrane protein which undergoes phosphorylation that is promoted by micromolar, but not millimolar, concentrations of cyclic AMP and which, when phosphorylated, undergoes dephosphorylation that is promoted by Ca2+. We suggest that this membrane component can participate in the modulation of the activity of the (Ca2+ + Mg2+)-dependent ATPase of the human erythrocyte.

Activation of solubilized liver membrane adenylate cyclase by nucleotides

AbstractLiver plasma membranes isolated from hypophysectomized rats were treated with 0.1 M Lubrol-PX, a nonionic detergent, and centrifuged at 165,000 × g for 1 hour. Adenylate cyclase activity remaining in the supernate had a specific activity that was at least equal to that of the particulate enzyme. The activity of the solubilized, non-sedimentable adenylate cyclase, as well as the membrane bound enzyme, was increased by GTP, ITP, and GMP-PCP at 10−4 M. The activity of the solubilized, non-sedimentable enzyme increased linearly with GTP from 10−6 to 10−4 M but there was no further increase in the activity of the solubilized enzyme with 10−3 M GTP. In contrast, the particulate liver membrane enzyme activity increased exponentially with GTP from 10−6 to 10−4 M and was further increased by 10−3 M GTP. These data indicate that GTP, ITP or GMP-PCP have direct effects on solubilized adenylate cyclase. This effect is in addition to a role of nucleotides in modifying membrane structure (16).

Effects of nutritional status and the pituitary on the acute plasma free fatty acid and glucose responses of rats to growth hormone administration☆

AbstractNormal and hypophysectomized rats, either in the fed or fasted state, were treated with bovine growth hormone (BGH) to determine whether the acute decline in plasma free fatty acids (FFA) and glucose in response to growth hormone (GH) administration could be modified by nutritional status and the presence of the pituitary. Both 1- and 3-mg. doses of BGH caused a plasma FFA diminution at 30 and 22 minutes, respectively, in hypophysectomized rats fasted for 24 hours. The hypolipemia observed with either dose of BGH was associated with an early fall in plasma glucose. The plasma glucose, however, did not subsequently return to normal levels during the 1-hour experimental period, as was the case with plasma FFA. At the higher dose of BGH plasma, FFA were markedly elevated above control levels at 1 hour, a condition indicative of the well-documented, secondary, hyper-lipemic response to GH treatment. The acute hypolipemic and hypoglycemic responses to BGH were not altered when hypophysectomized rats were used following a 42-hour fast. Hypophysectomized rats, which were not fasted, however, only exhibited the hypoglycemic response to BGH treatment; no alterations in plasma FFA levels were observed in these animals. Normal rats, either fed or fasted, showed neither the decline in plasma FFA nor of glucose following treatment with BGH. The time course of the acute hypolipemic and hypoglycemic effects of BGH in rats, when determined under the appropriate conditions of hypophysectomy and fasting, were further demonstrated to be functions of the preparation of BGH used.

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