The effect of selenium on the function of the anion transporter (Band 3) of erythrocyte membranes

The transport activity of Band 3 of spectrin-stripped inside-out erythrocyte membrane vesicles (IOVs) or resealed ghosts was enhanced in the presence of trace amounts of Na2SeO3 (0.2-0.5 p.p.m.); however, at higher concentrations of Na2SeO3 (> 4.0 p.p.m.), an inverse result was obtained. Reassociation of spectrin with IOVs has no effect either on the transport activity of Band 3 or on the enhancement of its activity by Na2SeO3. Sulfhydryl reagents (p-chloromercuribenzoic acid and N-ethylmaleimide) could also inhibit Band 3 activity and eliminate the selenium effect. It is suggested that SH groups are involved in anion transport of Band 3 and that the selenium effect is based on the interaction of SH groups of Band 3 with Na2SeO3.

Study of the lipid-protein interaction of F ATPases

Mg2+ may play a role in altering the lipid fluidity of the bilayers which would induce a change in conformation of the F0 portion of the H(+)-ATPase complex. This change could be transmitted to the soluble F1 portion, the conformation of which is in turn altered, resulting in higher enzymic activity. In addition to mitochondrial H(+)-ATPase, similar Mg2+ effects on the reconstitution of chloroplast H(+)-ATPase and other intrinsic membrane proteins have also been observed in our laboratory.

Effect of transmembrane Ca2+ gradient on conformation and enzyme activity of reconstituted adenylate cyclase

Adenylate cyclase from bovine brain cortex was reconstituted into asolectin liposomes with (500-fold) or without transmembrane Ca2+ gradient. The enzyme activity of four types of proteoliposomes (the active center of enzyme exposing outside) was compared. The highest adenylate cyclase activity was observed in the vesicles with outside lower Ca2+ concentration (approximately 10(-6) mol/L, similar to the physiological condition). If the transmembrane Ca2+ gradient was in the inverse direction (i.e. outside higher Ca2+ concentration, 0.5 mmol/L), a lowest enzymatic activity would appear. The difference in enzymatic activity between the two types of proteoliposomes could be diminished following the addition of Ca2+ ionophore A23187. Proteoliposomes without transmembrane Ca2+ gradient exhibited intermediate activities. The conformation difference of adenylate cyclases in the above-mentioned proteoliposomes was also detected by measuring intrinsic fluorescence and fluorescence quenching with KI.

A proper transmembrane Ca2+ gradient is essential for the higher enzymatic activity of adenylate cyclase

Adenylate cyclase from bovine brain cortex was reconstituted into liposomes with (1000 fold) or without transmembrane Ca2+ gradient. The highest enzyme activity (the active center of enzyme exposing outside) was observed in the vesicles with lower Ca2+ concentration outside (approximately 10(-6) M, similar to physiological condition). If the transmembrane Ca2+ gradient was in the inverse direction (i.e. higher Ca2+ concentration outside, 1 mM), a lowest enzyme activity would appear. Such a difference could be diminished following addition of A23187. Obtained results showed that a proper transmembrane Ca2+ gradient is essential for the optimal fluidity of phospholipid bilayer, favouring the formation of suitable conformation of adenylate cyclase with higher enzyme activity.

The role of Se in the interconversion of polymeric states of spectrin from human erythrocytes

It has been shown that Se can markedly prevent the dissociation of spectrin from erythrocyte ghosts. We now report that the transformation of incubated spectrin oligomers to its tetramers and dimers was obviously decreased in the presence of trace amounts (0.5-2.0 p.p.m.) of Na2SeO3. The spectrin tetramers and dimers are in a reversible equilibrium and Se could alter this equilibrium in favour of tetramers. This Se effect is concentration dependent and an inverse result was obtained with higher Na2SeO3 concentrations (greater than 4.0 p.p.m.). We suggest that the equilibrium state of the spectrin tetramer-dimer may be governed by a conformation adjustment induced by Se and the difference in conformation in the presence of low and high Na2SeO3 concentration may lead to an alteration of the spectrin tetramer-dimer balance.

Human hepatic regenerative stimulator substance: partial purification and biological characterization of hepatic stimulator substance from human fetal liver cells

Current support or replacement therapies for fulminant acute hepatic failure are frequently very disappointing. In this study, human hepatic stimulator substance--a liver-specific growth factor--was partially purified from human fetal liver cells and characterized by its biological effects. Almost 70-fold protein content was purified with an approximately 80-fold increase in specific growth stimulator activity. Human hepatic stimulator substance proved to be heat-stable, protease-sensitive, organ-specific and species-nonspecific. Human hepatic stimulator substance produced a two- to threefold increase of 3H-thymidine incorporation into hepatic DNA when injected intraperitoneally into growing weanling mice (nonhepatectomized) or regenerating rats (34% hepatectomy). The effects of hHSS in reversing the lethality of D-galactosamine (1.6 gm/kg body weight)-induced hepatic necrosis in rats were further evaluated. A survival rate of 4% (n = 24), 41% (n = 12, p less than 0.05), 33% (n = 12, p less than 0.05), 31% (n = 13, p less than 0.05) and 18% (n = 11, p greater than 0.05) was observed when the rats were injected with 4 ml of saline intraperitoneally, 4 ml of human intact fetal hepatocytes (2.4 x 10(8] intraperitoneally, 4 ml of human hepatic stimulator substance intraperitoneally, 2 ml of twofold concentrated human hepatic stimulator substance intravenously and 1 ml of fourfold human hepatic stimulator substance intramuscularly, respectively, 20 hr after poisoning.(ABSTRACT TRUNCATED AT 250 WORDS)

Further study on the role of Mg2+ in lipid-protein interaction in reconstituted porcine heart mitochondrial H+-ATPase

Porcine heart mitochondrial H+-ATPase was reconstituted by cholate dialysis method in liposomes containing neutral (PC, PE), acidic (PG, PI, PA, PS, DPG) or neutral and acidic phospholipids. The Mg2+ effect on the ATPase activity and its sensitivity to oligomycin, ATP-induced delta psi and delta pH formation was observed for the proteoliposomes containing acidic but not neutral phospholipids. Maleimide spin labels with varying arm lengths or bromoacetamide spin probe were used to monitor the conformational difference of H+-ATPase in the Mg2+-containing and Mg2+-'free' samples. A difference in W/S ratio (weakly immobilized/strongly immobilized component in the ESR spectra) could be detected for the F0.F1-containing and F1-depleted, (F0)-containing proteoliposomes, suggesting conformational difference in the F0-F1 complex and F0 portion induced by the Mg2+ effect. A conformational change of the beta-subunits in the F1 portion was also deduced from the ATP-induced fluorescence quenching of aurovertin-complex for Mg2+-containing samples. The results obtained are in favor of our previous assumption that Mg2+ may play its role by altering the physical state of the lipid bilayer, which would induce a conformational change in F0 (buried in the lipid core), which in turn is transmitted to the catalytic F1, resulting in a higher enzyme activity.

Reaction of Se with SH groups in spectrin is involved in the stabilization of erythrocyte membrane skeleton

Na2SeO3 supplementation in the dialysis medium could obviously prevent the dissociation of spectrin from the erythrocyte membranes. Such Se effect could be eliminated by pretreatment of erythrocyte membranes with a SH-blocking reagent, iodoacetamide(IAA) or addition of a SH-compound, dithio-threitol. The fluorescence intensity of erythrocyte membranes labelled with the fluorescent probe N-(3-pyrenyl)-maleimide decreased with increasing Na2SeO3 concentration used for pretreatment of ghosts. 31P-NMR spectra of erythrocyte membrane dialyzed in the presence or absence of Na2SeO3 concentration showed a difference in chemical shift anisotropy (delta sigma) between these two samples. These data suggest that the stabilization effect is based on changes in lipid-protein interaction and conformation of membrane skeletal components induced by reaction of their SH groups with Na2SeO3.

Keshan disease--an endemic mitochondrial cardiomyopathy in China

Keshan disease (KD) is a cardiomyopathy endemic in certain areas of China, characterized by severe deterioration and multiple focal necrosis. In the present paper we describe abnormalities of the structure and function of myocardial mitochondria from patients with subacute Keshan disease. Activities of succinate dehydrogenase, succinic oxidase, cytochrome c oxidase, H(+)-ATPase and its sensitivity to oligomycin and the response of membrane potential to energization by ATP were significantly decreased. However, the spectrum of reduced-minus-oxidized cytochromes in patients' mitochondria showed no obvious difference in the content of cytochrome c oxidase (aa3). There was also a marked decrease in lipid fluidity of affected mitochondria, and an abnormal amount of moderately electron dense amorphous inclusions. Electron-microscopic x-ray microanalysis and exposure to protein digestion reagent demonstrated that these inclusions are not Ca3(PO4)2, but are, probably, proteinaceous in nature. Affected mitochondria had markedly decreased selenium content. The defects in myocardial mitochondria from patients with chronic Keshan disease were less extensive than those in patients with subacute Keshan disease. We propose that Keshan disease be classified as a form of "mitochondrial cardiomyopathy".

Magnesium mediated change in physical state of phospholipid modulates membrane ATPase activity

During reconstitution of pig heart mitochondrial H(+)-ATPase in soybean phospholipid liposomes by the cholate dialysis method, Mg2+ greatly enhanced 32Pi-ATP exchange activity, ATPase activity and the sensitivity to oligomycin or DCCD of the reconstituted enzyme complex. The effect of Mg2+ on the lipid packing or fluidity of the reconstituted proteoliposomes was measured by means of spin labels, fluorescent probes and pyrene excimer formation efficiency. A difference in fluidity seemed to be localized near the polar faces of lipid bilayers of the reconstituted enzyme complex. Fluidity was less in the presence of Mg2(+)-containing and the Mg2(+)-'free' samples. Based on the results obtained a hypothetical scheme was proposed for Mg2(+)-mediated change in the physical state of phospholipid modulates incorporating H(+)-ATPase in liposomes. It postulated that Mg2+ may play a role in altering the lipid fluidity of the bilayers, which would induce a change of conformation of F0 portion (buried in the lipid core) of H(+)-ATPase complex. Such change could be transmitted to the soluble F1 portion, the conformation of which is in turn altered, resulting in higher enzymatic activity. Such an assumption was further supported by the results of a series of biochemical and biophysical experiments. Similar to its effect in the reconstitution of porcine heart mitochondrial H(+)-ATPase in liposomes, Mg2+ may also enhance the enzyme activity of reconstituted cytochrome C oxidase, porcine kidney medulla Na,K-ATPase, Ca-ATPase from rabbit sarcoplasmic reticulum and chloroplast H(+)-ATPase, in liposomes. It may be inferred that the structure and function of many membrane proteins are similarly modulated by Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Trachea-innominate artery fistula: retrospective comparison of treatment methods

A fistula between the trachea and the innominate artery, a potentially fatal complication of tracheostomy, can be managed successfully. We have derived several guidelines from our experience with one such case and from a review of the 36 cases reported in the literature over the last decade. Diagnosis must be established before exsanguination occurs. Bronchoscopy and angiography are often nondiagnostic. Control of hemorrhage and a patent airway are the initial goals of treatment. Interruption of the innominate artery is the definitive treatment, with a low rebleeding rate (7%, 1/14 cases) and good long-term survival (64%, 9/14 cases). Maintenance of continuity of the innominate artery is contraindicated, because of a high rebleeding rate (60%, 6/10 cases) and poor long-term survival (10%, 1/10 cases). There is no convincing evidence that interruption of the innominate artery causes significant neurologic or vascular compromise.

Role of Se in stabilization of human erythrocyte membrane skeleton

Na2SeO3 supplementation in the ageing medium could protect aged erythrocyte ghosts from decreases in lipid fluidity, Na, K-ATPase activity, and sensitivity to ouabain. Results also showed that Se could obviously prevent the dissociation of spectrin from the erythrocyte membrane. Furthermore, Se could markedly promote the reassociation of spectrin with the spectrin-stripped inside out membrane vesicles(IOVs) of erythrocytes. The protective action of Se on biomembranes is generally interpreted in terms of the activity of Se-containing glutathione peroxidase (GSHPx). However, since GSHPx is mainly distributed in the cytoplasm of erythrocytes, the stabilizing effect of Se on erythrocyte membranes might not be related to the activity of this enzyme.

Study on the interaction of Se and erythrocyte membrane--protective effect of Se on the erythrocyte membranes

During the ageing of erythrocyte membrane, the spectrin content, Na,K-ATPase activity as well as the lipid fluidity are obviously decreased. However, supplementation of a trace amount of Na2SeO3 in the medium could prevent the dissociation of spectrin from membrane and delay the changes of Na,K-ATPase activity and lipid fluidity. The effectiveness is proportional to Se concentration within the range of 0.1-1.0 ppm. Similar effect of supplementation of Se on the intact erythrocytes during ageing has been also observed. The protective action of Se on biomembranes is generally interpreted in terms of the activity of Se-containing glutathione peroxidase (GSHPx). However, GSHPx mainly distributes in the cytoplasma of erythrocytes, therefore it seems that the protective action of supplemented Se on the isolated erythrocyte membrane might not be related to the activity of GSHPx.

Comparison of the effect of scorpion venom (Buthus martensii Kashi) on the rat brain and heart mitochondria

A partially purified fraction SVc and a purified homogeneous polypeptide SVIII were isolated from the scorpion (Buthus martensii Kashi) venom, collected in Shan Dong Province of China. SVc decreased the RCR, ADP/O and Qo2 of the rat brain mitochondria. It also decreased the cytochrome oxidase activity and increased the membrane lipid fluidity of the mitochondria. Effect of scorpion venom on the rat heart mitochondria was somewhat different from that of rat brain mitochondria. SVc also decreased RCR, ADP/O and increased the membrane lipid fluidity of heart mitochondria. However, the Qo2 and cytochrome oxidase activity were increased. SVIII has a similar effect on the rat brain and heart mitochondria, but its concentration used is only 1/10 of the effective concentration of SVc.

Study on the interaction of Se and erythrocyte membrane--effect of Se on the Na, K-ATPase activity and fluidity of erythrocyte membranes

The content of binding-Se in erythrocyte membrane may affect its structure and function. Decrease in Se content will lead to a lower activity of Na, K-ATPase and lipid fluidity in ghosts, and a marked increase in Na, K-ATPase activity as well as lipid fluidity of erythrocyte membrane was observed by supplementation of low concentration of Na2SeO3 (0.03-0.3 ppm Se), in vitro. This effect was obvious only when the ghosts were incubated with Se at 0-4 degrees C for at least half an hour prior to assay.

Comparison of the effects of one-side- and two-side Mg2+ on the reconstitution of mitochondrial H+-ATPase

Three types of proteoliposome containing mitochondrial H+-ATPase have been prepared: Mg2+-'free', one-side and two-side Mg2+-containing proteoliposomes. The ATPase activity as well as its sensitivity to oligomycin or N,N'-dicyclohexylcarbodiimide of the three proteoliposome preparations has been compared. They decreased in the order: L X (H+-ATPase)+ Mg2+ greater than L X (H+-ATPase)-+ Mg2+ greater than L X (H+-ATPase)-Mg2+. The fluidity of the proteoliposomes has also been compared by fluorescence polarization probes diphenylhexatriene (DPH) or 7-(9-anthroyloxy)stearic acid (7-AS). The degree of polarization for DPH in these proteoliposomes decreased in the order: L X (H+-ATPase) +Mg2+ greater than L X (H+-ATPase)-+ Mg2+ greater than L X (H+-ATPase)-Mg2+, while that for 7-AS: L X (H+-ATPase) +Mg2+ approximately equal to L X (H+-ATPase)-+ Mg2+ greater than L X (H+-ATPase) -Mg2+.

Mg2+-mediated change in lipid fluidity enhances the reconstituted H+-ATPase activity

The results by using ANS fluorescent probe and spin labels 5-NS show that the fluidity of L. (H+-ATPase) +Mg2+ (H+-ATPase from pig heart mitochondria reconstituted in the presence of Mg2+) is less than that of L. (H+-ATPase) -Mg2+ (proteoliposome reconstituted in the absence of Mg2+). But no significant difference in fluidity has been observed when both reconstituted systems were monitored by using spin labels 12-NS and 16-NS. This indicates that Mg2+ may cause changes in fluidity of the lipid molecules near the surfaces of the bilayers, but does not affect significantly the fluidity of the deeper layer of the reconstituted system. It is tentatively supposed that in the presence of Mg2+, enhancement of activities of reconstituted H+-ATPase may be due to the Mg2+-mediated change in physical state of the lipids in the more superficial region of lipid bilayers so as to ensure a suitable conformation of ATPase complex, thereby possessing higher activity.

Studies on incorporation of membrane protein into liposomes--effect of divalent cations on reconstitution of pig heart mitochondrial H+-ATPase into liposomes

During the process of reconstitution of pig heart mitochondrial H+-ATPase on liposomes by cholate dialysis method, 1 mM Mg2+ in the dialysis medium can obviously increase activities of the reconstituted H+-ATPase (32Pi-ATP exchange, enzyme activity and its sensitivity to oligomycin or DCCD and ATP-dependent ANS 1) fluorescence). Besides Mg2+, effects of other divalent cations and spermidine on the H+-ATPase reconstitution have been compared. The effectiveness of the divalent cation activation of 32Pi-ATP exchange of the reconstituted H+-ATPase, decreased in the order: Mg2+ greater than Ca2+ greater than Mn2+ greater than Sr2+, while that of increasing the sensitivity to the inhibitors: Ca2+ greater than Mg2+ greater than Mn2+ greater than Sr2+. No significant effect on the H+-ATPase reconstitution has been found with Cd2+, Zn2+ and spermidine3+. Mechanism of action of the divalent cations on reconstitution has been discussed.

Purification and properties of the anticoagulant principle of Trimeresurus gramineus venom

By means of DEAE-Sephadex A-50 column chromatography, Trimeresurus gramineus venom was separated into 12 fractions. Fraction 8 had marked anticoagulant action in the tests of whole blood clotting time, calcium clotting time and plasma prothrombin time. Fraction 8 was rechromatographed on Sephadex G-100, then on DEAE-Sephadex A-50 again, and finally on Sephadex G-100, and a single peak was obtained. The patterns of microzone and disc electrophoresis also showed a single band. A single symmetrical boundary with 1.70 Svedberg units was obtained by ultracentrifugation. The estimated molecular weight was 19 500. The isoelectric point was pH 4.5. Chemical analysis showed that the anticoagulant principle was a glycoprotein and that it was thermolabile. The anticoagulant activity of this purified principle was 3.5 times higher than that of the crude venom. Fraction 5 potentiated its anticoagulant activity to 10 times higher than that of the crude venom. This principle did not possess caseinolytic, tosyl-L-arginine methyl ester esterase, phospholipase A, phosphodiesterase, alkaline phosphomonoesterase, fibrinolytic, hemorrhagic or local irritating activities. The purified anticoagulant principle did not destroy fibrinogen, induce fibrinolysis, inactivate thrombin nor interfere with the interaction between thrombin and fibrinogen. However, a marked inhibition of prothrombin activation was caused by the anticoagulant principle. The inhibition of prothrombin activation was not due to the destruction of prothrombin or its activation factors, but due to an interference in the interaction between prothrombin and its activation factors because of the reversible binding of these factors with the anticoagulant principle of the venom.