scholarly journals The specificity of yeast low-Km cyclic AMP phosphodiesterase towards free bivalent metal ions and the diastereoisomers of cyclic adenosine phosphorothioate

1985 ◽  
Vol 226 (3) ◽  
pp. 897-900 ◽  
Author(s):  
K Suoranta ◽  
J Londesborough
Keyword(s):  
Cyclic Amp ◽  
Metal Ions ◽  
Metal Ion ◽  
Relative Activity ◽  
Bivalent Metal ◽  
Cyclic Amp Phosphodiesterase ◽  
Bivalent Metal Ions

The relative activity of a zinc-containing cyclic AMP phosphodiesterase towards the (Sp)- compared with the (Rp)-diastereoisomer of cyclic adensine phosphorothioate varied with the identity of the free bivalent metal ion from more than 35 to 0.074 along the series Mg2+ greater than Mn2+ greater than Co2+ greater than Zn2+ greater than Cd2+, showing that this ion, and not the tightly bound zinc, bonds to the phosphorothioate moiety of the substrate.

scholarly journals Adenosine 3′:5′-cyclic monophosphate-dependent and plasma-membrane-associated protein kinase(s) from bovine corpus luteum. Properties of associated enzyme and phosphorylation of specific plasma-membrane proteins

1975 ◽  
Vol 151 (1) ◽  
pp. 23-36 ◽  
Author(s):  
S Azhar ◽  
K M Menon
Keyword(s):  
Plasma Membrane ◽  
Cyclic Amp ◽  
Metal Ions ◽  
Corpus Luteum ◽  
Protein Kinases ◽  
Ph Dependence ◽  
Bivalent Metal ◽  
Bovine Corpus Luteum ◽  
Km Value ◽  
Bivalent Metal Ions

Plasma-membrane fractions FI and FII isolated from bovine corpus luteum by discontinuous sucrose-density-gradient centrifugation, at sucrose-density interfaces of 1.14/1.16 and 1.16/1.18 respectively, contained membrane-associated protein kinases that phosphorylated both the structural proteins of membranes as well as exogenously added protein substrates. Both fractions were characterized with respect to endogenous and exogenous protein substrate specificity, pH-dependence, effect of bivalent metal ions and sensitivity toward cyclic nucleotides. These membrane-associated kinases showed an optimum pH of 6.0 and had an absolute requirement for bivalent metal ions such as Mg2+, Mn2+, or Co2+ that cannot be replaced by Ca2+. Both the activities were stimulated two- to four-fold by cyclic AMP in vitro with an apparent Km of 83 and 50 nM for fractions FI and FII respectively. Other cyclic 3′:5′-nucleotides were effective only at higher concentrations, but even the most effective, cyclic IMP, showed a stimulation nearly an order of magnitude lower than that of cyclic AMP. In contrast, stimulation by cyclic dTMP and cyclic dAMP was very weak. Cyclic AMP showed no significant effect on the apparent Km value of both enzymes for histone and MgCl2 but it somewhat decreased the Km value for ATP. Nucleoside triphosphates like GTP, CTP and UTP inhibited the transfer of [32P]Pi from [γ-32P]ATP into mixed histone catalysed by membrane-associated kinases either in the presence or in the absence of cyclic AMP. In addition to protein kinases, these membrane fractions also possessed cyclic AMP-binding activities. The apparent association constant (Kalpha) for cyclic AMP binding was 1.0 × 10(10) and 2.6 × 10(10) M for FI and FII membrane fractions respectively.

Degradation of Perfluoropolyether Fluids With Metal Ions

1999 ◽  
Vol 121 (2) ◽  
pp. 348-351 ◽  
Author(s):  
Takashi Fukuchi
Keyword(s):  
Metal Ions ◽  
Reaction Mechanisms ◽  
Metal Ion ◽  
Chemical Degradation ◽  
Bivalent Metal ◽  
Ether Cleavage ◽  
Cleavage Process ◽  
Metal Atoms ◽  
Bivalent Metal Ions ◽  
Fomblin Z

Chemical degradation of lubricant fluids of perfluoropolyether (PFPE), such as Fomblin Z-DOL, Fomblin AM-2001, Fomblin Z-25, Demnum SP-3, and Demnum SA, with bivalent metal ions was examined. The respective reaction mechanisms involve an ether cleavage process which is caused by the coordination of metal ions with oxygen atoms in the main chains of the PFPE. Metal ions were evaluated for their ability to degrade the PFPE, and the results demonstrate that the ions ranking in terms of this ability is as follows: Cu2+ > Ni2+ > Co2+ > Fe2+ > Mn2+ > Mg2+. This trend can be explained by the ionization potentials of the metal atoms. For an identical metal ion, the Demnum lubricants showed a greater stability than the Fomblin lubricants.

scholarly journals Activation of membrane-bound high-affinity calcium ion-sensitive adenosine triphosphatase of human erythrocytes by bivalent metal ions

1975 ◽  
Vol 147 (2) ◽  
pp. 359-361 ◽  
Author(s):  
H Pfleger ◽  
H U Wolf
Keyword(s):  
Metal Ions ◽  
Calcium Ion ◽  
Metal Ion ◽  
Adenosine Triphosphatase ◽  
Erythrocyte Membranes ◽  
Bivalent Metal ◽  
High Affinity ◽  
Human Erythrocyte Membranes ◽  
Bivalent Metal Ions ◽  
Membrane Bound

The Ca2+-sensitive ATPase (adenosine triphosphatase) of human erythrocyte membranes is activated, not only by Ca2+ ions, but also by a series of other bivalent metal ions including Sr2+, Ba2+, Mn2+, Ni2+, Co2+, Cd2+, Cu2+, Zn2+ and Pb2+. The degree of activation is dependent on the radius of the ion rather than on its nature, in contrast with the dissociation constant of the enzyme--metal ion complex.

scholarly journals The kinetics of bivalent metal ion dissociation from myosin subfragments

1986 ◽  
Vol 233 (1) ◽  
pp. 173-177 ◽  
Author(s):  
A J Bennett ◽  
C R Bagshaw
Keyword(s):  
Metal Ions ◽  
Rate Constant ◽  
Metal Ion ◽  
Specific Site ◽  
Ph Change ◽  
Bivalent Metal ◽  
Skeletal Muscle Myosin ◽  
Adductor Muscles ◽  
Bivalent Metal Ions ◽  
Muscle Myosin

Bivalent metal ions have multiple roles in subunit association and ATPase regulation in scallop adductor-muscle myosin. To help elucidate these functions, the rates of Ca2+ and Mg2+ dissociation from the non-specific high-affinity sites on the regulatory light chains were measured and compared with those of rabbit skeletal-muscle myosin subfragments. Ca2+ dissociation had a rate constant of about 0.7 s-1 in both species, as measured by the time course of the pH change on EDTA addition. Mg2+ dissociation had a rate constant of 0.05 s-1, as monitored by its displacement with the paramagnetic Mn2+ ion. It is concluded that the exchange between Ca2+ and Mg2+ at the non-specific site, on excitation of both skeletal and adductor muscles, is too slow to contribute to the activation itself. The release of bivalent metal ions from the non-specific site is, however, the first step in release of the scallop regulatory light chain (Bennett & Bagshaw (1986) Biochem. J. 233, 179-186). In scallop myosin additional specific sites are present, which can bind Ca2+ rapidly, to effect activation of the ATPase. In the course of this work, Ca2+ dissociation from EGTA was studied as a model system. This gave rates of 1 s-1 and 0.3 s-1 at pH 7.0 and pH 8.0 respectively.

scholarly journals Metal-ion-promoted binding of triazine dyes to proteins. The interaction of Cibacron Blue F3G-A with yeast hexokinase

1982 ◽  
Vol 205 (2) ◽  
pp. 453-456 ◽  
Author(s):  
P Hughes ◽  
R F Sherwood ◽  
C R Lowe
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Difference Spectroscopy ◽  
Bivalent Metal ◽  
Cibacron Blue ◽  
Transition Series ◽  
Bivalent Metal Ions ◽  
A Site ◽  
Active Site Region ◽  
Yeast Hexokinase

Bivalent metal ions, particularly Zn2+ and other members of the first-row transition series, promote irreversible inactivation of yeast hexokinase by Cibacron Blue F3G-A at a site competitive with both ATP and D-glucose. Difference spectroscopy indicates that the protein-dye dissociation constant is decreased from 250 micrometers in the absence of metal ions to less than 100 micrometers in the presence of appropriate concentrations of metal ions, with specificity displayed in the sequence of Zn2+ greater than Cu2+ greater than Ni2+ greater than Mn2+. Quantitative inactivation of yeast hexokinase leads to the incorporation of approx. 1 mol of Cibacron Blue F3G-A/mol of subunit of mol. wt. 51 000 in both the presence and the absence of metal ion. These results suggest the formation of a highly specific ternary complex involving enzyme, dye and metal ion at the active-site region of the enzyme, and correlate well with the known effects of metal ions in promoting the binding of hexokinase to immobilized Cibacron Blue F3G-A.

scholarly journals A stereochemical investigation of the hydrolysis of cyclic AMP and the (Sp)-and (Rp)-diastereoisomers of adenosine cyclic 3′:5′-phosphorothioate by bovine heart and baker's-yeast cyclic AMP phosphodiesterases

1982 ◽  
Vol 203 (2) ◽  
pp. 461-470 ◽  
Author(s):  
R L Jarvest ◽  
G Lowe ◽  
J Baraniak ◽  
W J Stec
Keyword(s):  
Cyclic Amp ◽  
Phosphorus Atom ◽  
Metal Ion ◽  
Baker’S Yeast ◽  
Baker's Yeast ◽  
Bivalent Metal ◽  
Cyclic Amp Phosphodiesterase ◽  
Bovine Heart ◽  
Hydrolysis Of

Bovine heart cyclic AMP phosphodiesterase, which has a requirement for Mg2+, hydrolyses cyclic AMP with inversion of configuration at the phosphorus atom, but only the (Sp)-diastereoisomer of adenosine cyclic 3′:5′-phosphorothioate is hydrolysed by this enzyme. By contrast, the low-affinity yeast cyclic AMP phosphodiesterase, which contains tightly bound Zn2+, hydrolyses both the (Sp)- and the (Rp)-diastereoisomers of adenosine cyclic 3′:5′-phosphorothioate, the (Rp)-diastereoisomer being the preferred substrate under V max. conditions. Both of the diastereoisomers of adenosine cyclic 3′:5′-phosphorothioate, as well as cyclic AMP, are hydrolysed with inversion of configuration at the phosphorus atom by the yeast enzyme. It is proposed that, with both enzymes, the bivalent metal ion co-ordinates with the phosphate residue of the substrate, and that hydrolysis is catalysed by a direct ‘in-line’ mechanism.

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