Cation and sequence effects on stability of intermolecular pyrimidine-purine-purine triplex.

A differential effect is found of various bivalent cations (Ba2+, Ca2+, Mg2+, Cd2+, Co2+, Mn2+, Ni2+, Zn2+ and Hg2+) on stability of intermolecular Py-Pu-Pu triplex with different sequence of base triads. Ca2+, Mg2+, Cd2+, Co2+, Mn2+, Ni2+ and Zn2+ do stabilize the d(C)n d(G)n d(G)n triplex whereas Ba2+ and Hg2+ do not. Ba2+, Ca2+, Mg2+ and Hg2+ destabilize the d(TC)n d(GA)n d(AG)n triplex whereas Cd2+, Co2+, Mn2+, Ni2+ and Zn2+ stabilize it. The complexes we observe are rather stable because they do not dissociate during time of gel electrophoresis in the co-migration experiments. Chemical probing experiments with dimethyl sulfate as a probe indicate that an arbitrary homopurine-homopyrimidine sequence forms triplex with corresponding purine oligonucleotide in the presence of Mn2+ or Zn2+, but not Mg2+. In the complex the purine oligonucleotide has antiparallel orientation with respect to the purine strand of the duplex. Specifically, we have shown the formation of the Py-Pu-Pu triplex in a fragment of human papilloma virus HPV-16 in the presence of Mn2+.     

Activation of three types of membrane currents by various divalent cations in identified molluscan pacemaker neurons

We investigated membrane currents activated by intracellular divalent cations in two types of molluscan pacemaker neurons. A fast and quantitative pressure injection technique was used to apply Ca2+ and other divalent cations. Ca2+ was most effective in activating a nonspecific cation current and two types of K+ currents found in these cells. One type of outward current was quickly activated following injections with increasing effectiveness for divalent cations of ionic radii that were closer to the radius of Ca2+ (Ca2+ greater than Cd2+ greater than Hg2+ greater than Mn2+ greater than Zn2+ greater than Co2+ greater than Ni2+ greater than Pb2+ greater than Sr2+ greater than Mg2+ greater than Ba2+). The other type of outward current was activated with a delay by Ca2+ greater than Sr2+ greater than Hg2+ greater than Pb2+. Mg2+, Ba2+, Zn2+, Cd2+, Mn2+, Co2+, and Ni2+ were ineffective in concentrations up to 5 mM. Comparison with properties of Ca2(+)-sensitive proteins related to the binding of divalent cations suggests that a Ca2(+)-binding protein of the calmodulin/troponin C type is involved in Ca2(+)-dependent activation of the fast-activated type of K+ current. Th sequence obtained for the slowly activated type is compatible with the effectiveness of different divalent cations in activating protein kinase C. The nonspecific cation current was activated by Ca2+ greater than Hg2+ greater than Ba2+ greater than Pb2+ greater than Sr2+, a sequence unlike sequences for known Ca2(+)-binding proteins.     

Intracellular hexose-6-phosphate:phosphohydrolase from Streptococcus lactis: purification, properties, and function.

An intracellular hexose 6-phosphate:phosphohydrolase (EC 3.1.3.2) has been purified from Streptococcus lactis K1. Polyacrylamide disc gel electrophoresis of the purified enzyme revealed one major activity staining protein and one minor inactive band. The Mr determined by gel permeation chromatography was 36,500, but sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single polypeptide of apparent Mr 60,000. The enzyme exhibited a marked preference for hexose 6-phosphates, and the rate of substrate hydrolysis (at 5 mM concentration) decreased in the order, galactose 6-phosphate greater than 2-deoxy-D-glucose 6-phosphate greater than fructose 6-phosphate greater than mannose 6-phosphate greater than glucose 6-phosphate. Hexose 1-phosphates, p-nitrophenylphosphate, pyrophosphate, and nucleotides were not hydrolyzed at a significant rate. In addition, the glycolytic intermediates comprising the intracellular phosphoenolpyruvate potential in the starved cells (phosphoenolpyruvate and 2- and 3-phosphoglyceric acids) were not substrates for the phosphatase. Throughout the isolation, the hexose 6-phosphate:phosphohydrolase was stabilized by Mn2+ ion, and the purified enzyme was dependent upon Mn2+, Mg2+, Fe2+, or Co2+ for activation. Other divalent metal ions including Pb2+, Cu2+, Zn2+, Cd2+, Ca2+, Ba2+, Sr2+, and Ni2+ were unable to activate the enzyme, and the first four cations were potent inhibitors. Enzymatic hydrolysis of 2-deoxy-D-glucose 6-phosphate was inhibited by fluoride when Mg2+ was included in the assay, but only slight inhibition occurred in the presence of Mn2+, Fe2+, or Co2+. The inhibitory effect of Mg2+ plus fluoride was specifically and completely reversed by Fe2+ ion. The hexose 6-phosphate:phosphohydrolase catalyzes the in vivo hydrolysis of 2-deoxy-D-glucose 6-phosphate in stage II of the phosphoenolpyruvate-dependent futile cycle in S. lactis (J. Thompson and B. M. Chassy, J. Bacteriol. 151:1454-1465, 1982).     

Purification and characterization of a Ca2+/calmodulin-dependent protein kinase from rat brain

A soluble Ca2+/calmodulin-dependent protein kinase has been purified from rat brain to near homogeneity by using casein as substrate. The enzyme was purified by using hydroxylapatite adsorption chromatography, phosphocellulose ion-exchange chromatography, Sepharose 6B gel filtration, affinity chromatography using calmodulin-Sepharose 4B, and ammonium sulfate precipitation. On sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gels, the purified enzyme consists of three protein bands: a single polypeptide of 51 000 daltons and a doublet of 60 000 daltons. Measurements of the Stokes radius by gel filtration (81.3 +/- 3.7 A) and the sedimentation coefficient by sucrose density sedimentation (13.7 +/- 0.7 S) were used to calculate a native molecular mass of 460 000 +/- 29 000 daltons. The kinase autophosphorylated both the 51 000-dalton polypeptide and the 60 000-dalton doublet, resulting in a decreased mobility in NaDodSO4 gels. Comparison of the phosphopeptides produced by partial proteolysis of autophosphorylated enzyme reveals substantial similarities between subunits. These patterns, however, suggest that the 51 000-dalton subunit is not a proteolytic fragment of the 60 000-dalton doublet. Purified Ca2+/calmodulin-dependent casein kinase activity was dependent upon Ca2+, calmodulin, and ATP X Mg2+ or ATP X Mn2+ when measured under saturating casein concentrations. Co2+, Mn2+, and La3+ could substitute for Ca2+ in the presence of Mg2+ and saturating calmodulin concentrations. In addition to casein, the purified enzyme displayed a broad substrate specificity which suggests that it may be a "general" protein kinase with the potential for mediating numerous processes in brain and possibly other tissues.     

The effect of monovalent and divalent cations on the activity of Streptococcus lactis C10 pyruvate kinase.

The pyruvate kinase (ATP: pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis C10 had an obligatory requirement for both a monovalent cation and divalent cation. NH+4 and K+ activated the enzyme in a sigmoidal manner (nH =1.55) at similar concentrations, whereas Na+ and Li+ could only weakly activate the enzyme. Of eight divalent cations studied, only three (Co2+, Mg2+ and Mn2+) activated the enzyme. The remaining five divalent cations (Cu2+, Zn2+, Ca2+, Ni2+ and Ba2+) inhibited the Mg2+ activated enzyme to varying degrees. (Cu2+ completely inhibited activity at 0.1 mM while Ba2+, the least potent inhibitor, caused 50% inhibition at 3.2 mM). In the presence of 1 mM fructose 1,6-diphosphate (Fru-1,6-P2) the enzyme showed a different kinetic response to each of the three activating divalent cations. For Co2+, Mn2+ and Mg2+ the Hill interaction coefficients (nH) were 1.6, 1.7 and 2.3 respectively and the respective divalent cation concentrations required for 50% maximum activity were 0.9, 0.46 and 0.9 mM. Only with Mn2+ as the divalent cation was there significatn activity in the absence of Fru-1,6-P2. When Mn2+ replaced Mg2+, the Fru-1,6-P2 activation changed from sigmoidal (nH = 2.0) to hyperbolic (nH = 1.0) kinetics and the Fru-1,6-P2 concentration required for 50% maximum activity decreased from 0.35 to 0.015 mM. The cooperativity of phosphoenolpyruvate binding increased (nH 1.2 to 1.8) and the value of the phosphoenolpyruvate concentration giving half maximal velocity decreased (0.18 to 0.015 mM phosphoenolyruvate) when Mg2+ was replaced by Mn2+ in the presence of 1 mM Fru-1,6-P2. The kinetic response to ADP was not altered significantly when Mn2+ was substituted for Mg2+. The effects of pH on the binding of phosphoenolpyruvate and Fru-1,6-P2 were different depending on whether Mg2+ or Mn2+ was the divalent cation.     

Stringent requirement for Ca2+ in the removal of Z-lines and alpha-actinin from isolated myofibrils by Ca2+-activated neutral proteinase

Treatment of isolated myofibrils with Ca2+-activated neutral proteinase (CANP) results in specific removal of Z-line and of alpha-actinin. To investigate the ionic requirement for these processes, we measured Z-line removal by phase-contrast and interference microscopy and alpha-actinin removal by sodium dodecyl sulphate/polyacrylamide-gel electrophoretic analysis of myofibrillar proteins. The proteolytic digestion of native purified proteins was measured directly on polyacrylamide gels and by the fluorescamine technique. We found that the removal of Z-line and alpha-actinin as well as the release of proteolytic degradation products from isolated myofibrils by CANP occur only in the presence of Ca2+; Sr2+, Ba2+, Mn2+, Mg2+, Co2+ and Zn2+ are all ineffective. In contrast with this stringent requirement for Ca2+, the proteolytic activity of CANP measured with denatured casein, native and denatured haemoglobin, native actin and tropomyosin also occurs in the presence of other bivalent cations, in the following order: Ca2+ greater than Sr2+ greater than Ba2+. These data suggest that only Ca2+ can produce the conformational change in myofibrils that renders them susceptible to the action of CANP, whereas its proteolytic activity is stimulated by several bivalent ions.     

The effect of divalent cations on bovine spermatozoal adenylate cyclase activity.

The effect of divalent cations on bovine sperm adenylate cyclase activity was studied. Mn2+, Co2+, Cd2+, Zn2+, Mg2+ and Ca2+ were found to satisfy the divalent cation requirement for catalysis of the bovine sperm adenylate cyclase. These divalent cations in excess of the amount necessary for the formation of the metal-ATP substrate complex were found to stimulate the enzyme activity to various degrees. The magnitude of stimulation at saturating concentrations of the divalent cations was strikingly greater with M2+ than with either Ca2+, Mg2+, Zn2+, Cd2+ or Co2+. The apparent Km was lowest for Zm2+ (0.1 - 0.2 mM) than for any of the other divalent cations tested (1.2 - 2.3 mM). The enzyme stimulation by Mn2+ was decreased by the simultaneous addition of Co2+, Cd2+, Ni2+ and particularly Zn2+ and Cu2+. The antagonism between Mn2+ and Cu2+ or Zn2+ appeared to have both competitive and non-competitive features. The inhibitory effect of Cu2+ on Mn2+-stimulated adenylate cyclase activity was prevented by 2,3-dimercaptopropanol, but not by dithiothreitol, L-ergothioneine, EDTA, EGTA or D-penicillamine. Ca2+ at concentrations of 1-5 mM was found to act synergistically with Mg2+, Zn2+, Co2+ and Mn2+ in stimulating sperm adenylate cyclase activity. The Ca2+ augmentation of the stimulatory effect of Zn2+, Co2+, Mg2+ and Mn2+ appeared to be specific.     

Effects of cations on guanylate cyclase of sea urchin sperm.

Mn2+ and to some degree Fe2+, but not Mg+, Ca2+, ba2+, Sr2+, Co2+, Ni2+, La3+, or Fe3+ were able to serve as effective metal cofactors for sea urchin sperm guanylate cyclase. The apparent Michaelis constant for Mn2+ in the presence of 0.25 mM MnGTP was 0.23 mM. In the presence of a fixed free mn2+ concentration, variation in mngTP resulted in sigmoid velocity-substrate plots and in reciprocal plots that were concave upward. These positive cooperative patterns were observed at both pH 7.0 and 7.8 and in the presence or absence of Triton X-100. When Mn2+ and GTP were equimolar, Ca2+, Ba2+, Sr2+, and Mg2+ increased apparent guanylate cyclase activity. This increase in enzyme activity at least could be accounted for partially by an increase in free Mn2+ concentration caused by the complex formation of GTP with the added metals. However, even at relatively low GTP concentrations and with Mn2+ concentrations in excess of GTP, Ca2+, Sr2+, and Ba2+ significantly increased guanosine 3':5'-monophosphate production. As the total GTP concentration was increased, the degree of stimulation in the presence of Ca2+ decreased, despite maintenance of a fixed total concentration of Ca2+ and a fixed free concentration of Mn2+, suggesting that the concentration of CaGTP and MnGTP were determining factors in the observed response. The concave upward reciprocal plots of velocity against MnGTP concentration were changed to linear plots in the presence of CaGTP or SrGTP. These results suggest that sea urchin sperm guanylate cyclase contains multiple nucleotide binding sites and that stimulation of guanosine 3':5'-monophosphate synthesis by Ca2+, Sr2+, and perhaps other metals may reflect interaction of a metal-GTP complex with enzyme as either an effector or a substrate.     

Assay and properties of N-acetylglucosamine-6-phosphate deacetylase from rat liver

A single-vial assay has been developed for N-acetylglucosamine-6-phosphate deacetylase, in which [3H]acetate released from 3H-acetyl-labeled substrate is measured in a biphasic liquid scintillation counting system after acidification of the reaction mixture. The deacetylase was partially purified from rat liver, and some of its properties were determined. Chromatography on a calibrated Sepharose CL-6B column indicated a molecular weight of 345,000. The Km for the substrate at pH 8.0 was 0.3 mM. Glucosamine 6-phosphate and glucose 6-phosphate inhibited the enzyme, whereas N-acetylgalactosamine, N-acetylglucosamine, N-acetylglucosamine 1-phosphate, and glucosamine 1-phosphate were without effect. The effects of several divalent cations were also examined. Under the conditions tested, Ca2+, Mg2+, and Ba2+ had essentially no effect, whereas Mn2+, Ni2+, and Cu2+ were inhibitory and Co2+ stimulated activity at low concentrations but inhibited above 5 mM. An increase in the ionic strength of the reaction mixture to 0.3 M decreased the activity by 40%.     

An equilibrium study of metal ion binding to human plasma coagulation factor XIII.

1. The binding of Ca2+ to plasma coagulation Factor XIII from man and from cow caused a small decrease in the intrinsic fluorescence of the protein with a dissociation constant of 0.1 mM. A similar decrease was observed with the thrombin-activated Factors (Factors XIIa). The decrease in protein fluorescence was also caused by both Ni2+ and Mn2+ but not by Mg2+. 2. 45Ca2+ binding was directly demonstrated by equilibrium dialysis. Ca2+ at 0.2 mM bound to Factor XIII (a2b2) and Factor XIIIa (a'2b2) but not to isolated b2-protein. A tight-binding site for Ca2+ is associated with the a-subunits. 3. The Ca2+ essential for the enzyme activity of Factor XIII from man, pig and cow can be replaced by Ni2+, Cu2+, La3+, Mn2+, Fe3+, Y3+, Co2+, Sr2+ or Tb3+, but not by Mg2+.     

Appearance of magnesium guanylate cyclase activity in rat liver with sodium azide activation.

Native soluble and particulate guanylate cyclase from several rat tissues preferred Mn2+ to Mg2+ as the sole cation cofactor. Wtih 4mM cation, activities with Mg2+ were less than 25% of the activities with Mn2+. The 1 mM NaN3 markedly increased the activity of soluble and particulate preparations from rat liver. Wtih NaN3 activation guanylate cyclase activities wite similar with Mn2+ and Mg2+. Co2+ was partially effective as a cofactor in the presence of NaN3, while Ca2+ was a poor cation with or without NaN3. Activities with Ba, Cu2+, or Zn2+ were not detectable without or with 1 mM NaN3. With soluble liver enzyme both manganese and magnesium activities were dependent upon excess Mn2+ or Mg2+ at a fixed MnGTP or MgGTP concentration of 0.4 mm; apparent Km values for excess Mn2+ and Mg2+ were 0.3 and 0.24 mM, respectively. After NaN3 activation, the activity was less dependent upon free Mn2+ and retained its dependence for free Mg2+, at 0.4 mM MgGTP the apparent Km for excess Mg2+ was 0.3 mM. The activity of soluble liver guanylate cyclase assayed with Mn2+ or Mg2+ was increased with Ca2+. After NaN3 activiation, Ca2+ had no effect or was somewhat inhibitory with either Mn2+. After NaN activation, Ca2+ had no effect or was somewhat inhibitory with either Mn2+ or Mg2+. The stimulatory effect of NaN2 on Mn2+-and Mg2+-dependent guanylate cyclase activity from liver or cerebral cortex supernatant fractions required the presence of the sodium azide-activator factor. With partially purified soluble liver guanylate cyclase and azide-activator factor, the concentration (1 mjM) of NaN3 that gave half-maximal activation with Mn2+ or Mg2+ was imilar. Thus, under some conditions guanylate cyclase can effectively use Mg2+ as a sole cation cofactor.     

Oxidoreductase activities of polyclonal IgGs from the sera of Wistar rats are better activated by combinations of different metal ions

It was shown that IgGs purified from the sera of healthy Wistar rats contain several different bound Me2+ ions and oxidize 3,3'-diaminobenzidine through a H2O2-dependent peroxidase and H2O2-independent oxidoreductase activity. IgGs have lost these activities after removing the internal metal ions by dialysis against EDTA. External Cu2+ or Fe2+ activated significantly both activities of non-dialysed IgGs containing different internal metals (Fe > or = Pb > or = Zn > or = Cu > or = Al > or = Ca > or = Ni > or = Mn > Co > or = Mg) showing pronounced biphasic dependencies corresponding to approximately 0.1-2 and approximately 2-5 mM of Me2+, while the curves for Mn2+ were nearly linear. Cu2+ alone significantly stimulated both the peroxidase and oxidoreductase activities of dialysed IgGs only at high concentration (> or = 2 mM), while Mn2+ weakly activated peroxidase activity at concentration >3 mM but was active in the oxidoreductase oxidation at a low concentration (<1 mM). Fe2+-dependent peroxidase activity of dialysed IgGs was observed at 0.1-5 mM, but Fe2+ was completely inactive in the oxidoreductase reaction. Mg2+, Ca2+, Zn2+, Al2+ and especially Co2+ and Ni2+ were not able to activate dialysed IgGs, but slightly activated non-dialysed IgGs. The use of the combinations of Cu2+ + Mn2+, Cu2+ + Zn2+, Fe2+ + Mn2+, Fe2+ + Zn2+ led to a conversion of the biphasic curves to hyperbolic ones and in parallel to a significant increase in the activity as compared with Cu2+, Fe2+ or Mn2+ ions taken separately; the rates of the oxidation reactions, catalysed by non-dialysed and dialysed IgGs, became comparable. Mg2+, Co2+ and Ni2+ markedly activated the Cu2+-dependent oxidation reactions catalysed by dialysed IgGs, while Ca2+ inhibited these reactions. A possible role of the second metal in the oxidation reactions is discussed.     

The role of ATP and divalent cations in the regulation of a cardiac phosphorylase phosphatase (phosphoprotein phosphatase) of Mr = 35,000.

The effects of ATP and divalent cations on a divalent cation-independent phosphorylase phosphatase of Mr = 35,000 (phosphatase S) purified from canine cardiac muscle have been studied. The enzyme can be rapidly inactivated by ATP or other nucleoside di- and triphosphates and PPi, but not by AMP, adenosine, adenine, Pi, EDTA, ethylene glycol bis(beta-aminoethyl ether)N,N' -tetraacetic acid, 1,10-phenanthroline, or 8-hydroxyquinoline. After removing the inactivating agent, such as ATP or PPi, by gel filtraiton followed by exhaustive dialysis, the inactivated enzyme (apophosphatase S) can be reactivated by preincubating with Mn2+ or Co2+, but not with Mg2+, Ca2+, Ni2+, Zn2+, Fe2+, Cu2+, Ba2+, Hg2+, Pb2+, or Cd2+. The Mn2+ -reactivated enzyme, which is less active than the Co2+ -reactivated enzyme, can be again inactivated by preincubating with ATP. The present findings indicate that phosphatase S contains a tightly bound divalent cation, probably Mn2+, in the active site. ATP and PPi, due to their structural similarity to the phosphoprotein substrate and their ability to chelate metal ions, can readily enter the active site to remove the divalent cation(s) essential for the catalytic function. The present findings also indicate that phosphatase S, a common catalytic subunit of several larger molecular forms of nospecific phosphoprotein phosphatase in cardiac muscle, can exist in two interconvertible forms, a metallized form (active) and a demetallized form (inactive). ATP and metal ions may regulate this class of isozymes by mediating the interconversions.     

Purification, quaternary structure, composition, and properties of D-ribulose-1,5-bisphosphate carboxylase from Thiobacillus intermedius.

D-Ribulose-1,5-bisphosphate (RuBP) carboxylase has been purified from glutamate-CO2-S2O3(2)-grown Thiobacillus intermedius by pelleting the enzyme from the high-speed supernatant and by intermediary crystallization followed by sedimentation into a discontinuous 0.2 to 0.8 M sucrose gradient. The enzyme was homogeneous by the criteria of electrophoresis on polyacrylamide gels of several acrylamide concentrations, sedimentation velocity and equilibrium measurements, and electron microscopic observations of negatively stained preparations. The molecular weights of the enzyme determined by sedimentation equilibrium and light-scattering measurements averaged 462,500 +/- 13,000. The enzyme consisted of closely similar or identical polypeptide chains of a molecular weight of 54,500 +/- 5,450 determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The S(0)20,w of the enzyme was 18.07S +/- 0.22. Electron microscopic examination suggested that the octomeric enzyme (inferred from the molecular measurements mentioned) had a cubical structure. The specific activity of the enzyme was 2.76 mumol of RuBP-dependent CO2 fixed/min per mg of protein (at pH 8 and 30 C), and the turnover number in terms of moles of CO2 fixed per mole of catalytic site per second was 2.6. The enzyme was stable for 3 months at -20 C and at least 4 weeks at 0 C. The apparent Km for CO2 was 0.75 mM, and Km values for RuBP and Mg2+ were 0.076 and 3.6 mM, respectively. Dialyzed enzyme could be fully reactivated by the addition of 20 mM Mg2+ and partially reactivated by 20 mM Co2+, but Cd2+, Mn2+, Ca2+, and Zn2+ had no effect. The compound 6-phosphogluconate was a linear competitive inhibitor with respect to RuBP when it had been preincubated with enzyme, Mg2+, and HCO3-.     

Physicochemical characterization of the microbial Fe2+ chelator proferrorosamine from Pseudomonas roseus fluorescens.

The microbial chelating compound proferrorosamine A, produced by Pseudomonas roseus fluorescens, formed a complex with Fe2+ of which the apparent stability constant was found to be 10(23). The following order of increasing stability constants of metal complexes with proferrorosamine was established as: Ba2+, Ca2+, Mg2+, Mn2+ less than Hg2+ less than Zn2+ less than Pb2+ less than Co2+ less than Cu2+ congruent to Fe2+ less than Ni2+. Only Ni(2+)-proferrorosamine had a stability constant which was established as: Ba2+, Ca2+, Mg2+, Mn2+ less than Hg2+ less than Zn2+ less than Pb2+ less than Co2+ less than Cu2+ congruent to Fe2+ less than Ni2+. Only Ni(2+)-proferrorosamine had a stability constant which was ca 32 times higher than Fe(2+)-proferrorosamine. Because of the production of proferrorosamine the growth of Ps. roseus fluorescens was not inhibited in iron limiting media by the addition of 0.15 mmol/l of the weaker chemical Fe2+ chelator 2,2'-dipyridyl. This contrasted with the proferrorosamine-negative mutant K2 and Ps. stutzeri, which only produces Fe(3+)-chelating siderophores. Furthermore, it was found that proferrorosamine was able to dissolve Fe2+ from stainless steel. These results show that proferrorosamine is a strong and selective Fe2+ chelator which could be used as an alternative for the toxic 2,2'-dipyridyl to control lactic acid fermentations.     

Effect of bivalent metal ions on the fluctuations of ion currents in rat liver mitochondria

Ions of bivalent metals are shown to arrange in the Sr2+ greater than Ca2+ greater than Ba2+ greater than Mn2+ series as to their ability to induce ion flow vibration in the rat liver mitochondria. Application of Sr2+ results in the most stable prolonged vibrations of ion flows in mitochondria. Ca2+, Ba2+ and Mn2+ induce slightly pronounced and intensively damped vibrations. The studied Mg2+, Co2+, Ni2+, Pb2+ Fe2+ cations have effect on valinomycin-induced K+ transport in mitochondria and do not induce vibrations. It is established that the ability of bivalent cations to induce vibrations is associated with the possibility of their transfer through the mitochondrion membrane and accumulation in the matrix. Inhibitors of the electrogenic Ca2+ transport in mitochondria produce the similar effect on vibrations induced by Sr2+, Ca2+, Ba2+ and Mn2+.     

Enhancement of adenosine triphosphatase activity of purified chloroplast coupling factor 1 in aqueous organic solvent

The ATPase activity of purified coupling factor 1 (CF1) of spinach chloroplasts [EC 3.6.1.3] was reversibly enhanced in some aqueous organic solvents, notably methanol, ethanol, and acetone. Pretreatment of CF1 with 20% (v/v) methanol did not affect the subsequent activity. The activity depended entirely on the final concentration of methanol in the reaction mixture. In the presence of 20% methanol, the Km of Ca2+-ATPase from ATP was lowered from 0.4 mM to 0.2 mM. Not only Ca2+, but also Cd2+, Mg2+, Mn2+, and Zn2+ supported the ATPase activity at rates of higher than 7 mumol.mg protein-1 . min-1. Co2+, Ni2+, and Pb2+ supported the activity at rates of 0.5-1.0 mumol.mg protein-1 . min-1. The activities supported by the following cations, if any, were less than 0.2 mumol.mg protein-1 . min-1; Ba2+, Cu2+, Fe2+, Hg2+, Sn2+, and Sr2+. The optimum concentration of methanol for Ca2+-ATPase and Mg2+-ATPase activities was about 30% (v/v). The optimum pH values for Ca2+-ATPase and Mg2+-ATPase activities were about 8.0 and 8.8, respectively. The enhancing effect of organic solvents appears to be associated with their relative lipophilic character as defined by the octanol-water partition coefficient. The Ca2+-ATPase activities of th trypsin-activated and the heat-activated CF1 were inhibited and their Mg2+-ATPase activities were enhanced by the presence of methanol in the reaction mixture.     

Purification and properties of urease from bovine rumen.

Urease (urea amidohydrolase, EC 3.5.1.5) was extracted from the mixed rumen bacterial fraction of bovine rumen contents and purified 60-fold by (NH4)2SO4 precipitation, calcium phosphate-gel adsorption and chromatography on hydroxyapatite. The purified enzyme had maximum activity at pH 8.0. The molecular weight was estimated to be 120000-130000. The Km for urea was 8.3 X 10(-4) M+/-1.7 X 10(-4) M. The maximum velocity was 3.2+/-0.25 mmol of urea hydrolysed/h per mg of protein. The enzyme was stabilized by 50 mM-dithiothreitol. The enzyme was not inhibited by high concentrations of EDTA or phosphate but was inhibited by Mn2+, Mg2+, Ba2+, Hg2+, Cu2+, Zn2+, Cd2+, Ni2+ and Co2+. p-Chloromercuribenzenesulfphonate and N-ethylmaleimide inhibited the enzyme almost completely at 0.1 mM. Hydroxyurea and acetohydroxamate reversibly inhibited the enzyme. Polyacrylamide-gel electrophoresis showed that the mixed rumen bacteria produce ureases which have identical molecular weights and electrophoretic mobility. No multiple forms of urease were detected.     

Regulation by divalent cations of 3H-baclofen binding to GABAB sites in rat cerebellar membranes

When investigating the effects of divalent cations (Mg2+, Ca2+, Sr2+, Ba2+, Mn2+ and Ni2+) on 3H-baclofen binding to rat cerebellar synaptic membranes, we found that the specific binding of 3H-baclofen was not only dependent on divalent cations, but was increased dose-dependently in the presence of these cations. The effects were in the following order of potency: Mn2+ congruent to Ni2+ greater than Mg2+ greater than Ca2+ greater than Sr2+ greater than Ba2+. Scatchard analysis of the binding data revealed a single component of the binding sites in the presence of 2.5 mM MgCl2, 2.5 mM CaCl2 or 0.3 mM MnCl2 whereas two components appeared in the presence of 2.5 mM MnCl2 or 1 mM NiCl2. In the former, divalent cations altered the apparent affinity (Kd) without affecting density of the binding sites (Bmax). In the latter, the high-affinity sites showed a higher affinity and lower density of the binding sites than did the single component of the former. As the maximal effects of four cations (Mg2+, Ca2+, Mn2+ and Ni2+) were not additive, there are probably common sites of action of these divalent cations. Among the ligands for GABAB sites, the affinity for (-), (+) and (+/-) baclofen, GABA and beta-phenyl GABA increased 2-6 fold in the presence of 2.5 mM MnCl2, in comparison with that in HEPES-buffered Krebs solution (containing 2.5 mM CaCl2 and 1.2 mM MgSO4), whereas that for muscimol was decreased to one-fifth. Thus, the affinity of GABAB sites for its ligands is probably regulated by divalent cations, through common sites of action.     

Purification and characterization of a calcium-calmodulin-dependent phospholamban kinase from canine myocardium

A Ca2+-calmodulin-dependent protein kinase was purified to apparent homogeneity from the cytosolic fraction of canine myocardium, with phospholamban as substrate. Purification involved sequential chromatography on DEAE-cellulose, calmodulin-agarose, DEAE-Bio-Gel A, and phosphocellulose. This procedure resulted in a 987-fold purification with a 5.4% yield. The purified enzyme migrated as a single band on native polyacrylamide gels, and it exhibited an apparent molecular weight of 550,000 upon gel filtration. Gel electrophoresis under denaturing conditions revealed a single protein band with Mr 55,000. The purified kinase could be autophosphorylated in a Ca2+-calmodulin-dependent manner, and under optimal conditions, 6 mol of Pi was incorporated per mole of 55,000-dalton subunit. The activity of the enzyme was dependent on Ca2+, calmodulin, and ATP.Mg2+. Other ions which could partially substitute for Ca2+ in the presence of Mg2+ and saturating calmodulin concentrations were Sr2+ greater than Mn2+ greater than Zn2+ greater than Fe2+. The substrate specificity of the purified Ca2+-calmodulin-dependent protein kinase for cardiac proteins was determined by using phospholamban, troponin I, sarcoplasmic reticulum membranes, myofibrils, highly enriched sarcolemma, and mitochondria. The protein kinase could only phosphorylate phospholamban and troponin I either in their purified forms or in sarcoplasmic reticulum membranes and myofibrils, respectively. Exogenous proteins which could also be phosphorylated by the purified protein kinase were skeletal muscle glycogen synthase greater than gizzard myosin light chain greater than brain myelin basic protein greater than casein. However, phospholamban appeared to be phosphorylated with a higher rate as well as affinity than glycogen synthase.(ABSTRACT TRUNCATED AT 250 WORDS)