bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interconvertible Forms of Phosphofructokinase of Rabbit Liver
Authors: Ramaiah Abburi , Tejwani Gopi A. 
Published: March 2005

When the phosphofructokinase reaction was started with the addition of stock rabbit liver phosphofructokinase its activity declined rapidly, at low concentrations of fructose 6‐phosphate or at high concentrations of ATP. The rate of this decline is independent of enzyme concentration and it could be prevented by the presence of positive effectors of the enzyme or by high concentration of fructose 6‐phosphate.When the reaction rate was measured in the first few seconds after addition of stock enzyme, the activity of the enzyme and its [S]0.5 value (concentration of fructose 6‐phosphate for half maximal velocity) were not affected significantly by the presence of positive effectors of the enzyme.The stock enzyme, which was routinely stored in the presence of 0.7 M (NH4)2SO4, 10 mM K2HPO4, 10 mM ATP, 50 mM Tris‐HCl pH 7.5 and 0.33 mM EDTA, was transformed to a less active form of enzyme, which had a very high [S]0.5 value and low intrinsic activity on dilution or when freed of effectors by passing the enzyme solution through a Sephadex G‐25 column. This form can be converted back to the active form by the positive effectors of the enzyme. The rate of this conversion of less active form to the active form of enzymes is again independent of enzyme concentration.The rate‐limiting step in the interconversions of active form to less active form of enzyme or vice versa is a first‐order process and there appears to be no aggregation or disaggregation of the enzyme during these interconversions.A variety of [S]0.5 values and maximal velocities were observed for the enzyme depending on the preincubation, prior dilution and removal of the effectors of enzyme suggesting the existence of at least two conformational states of enzyme in varying proportions differing widely in their [S]0.5 values and their intrinsic activities.These results are interpreted in terms of the model of Monod et al. for allosteric enzymes with minor modifications and the hysteretic concept of Frieden.
The Active Hexose‐Uptake System of Chlorella vulgaris
Authors: Komor Ewald , Haass Dieter , Komor Brunhild , Tanner Widmar 
Published: March 2005

The Km value for 6‐deoxyglucose influx into Chlorella vulgaris was found to be 0.21 mM and for efflux it was 21 mM. The sugar was accumulated up to 1500‐fold, an accumulation which cannot be explained by the difference in Km values.Using these Km values together with estimated relative translocation constants for carrier and carrier‐substrate it was possible to determine Ks values. The Ks value thus obtained for the carrier at the inner side of the membrane was 70 times larger than that on the outer side.Although different Km values to the ones given above for influx as well as for efflux were obtained when the measurements were carried out in the presence of high sugar concentrations at the opposite side of the membrane, the calculations yielded almost identical Ks values (Table 3).The experimentally observed accumulation of 6‐deoxyglucose can be well explained when the different Ks values and the estimated difference of 25‐fold between the translocation constants for outward as compared to inward “movement” of free carrier is considered.
Transport of Hexoses in Streptomyces violaceoruber
Authors: Sabater Bartolomé , Asensio Carlos 
Published: March 2005

Transport of glucose, mannose and fructose has been studied in spores and mycelia of Streptomyces violaceroruber grown under a variety of nutritional conditions.
Each of the three sugars is transported into mycelial cells by a specific, constitutive transport system. The apparent Michaelis constants of these systems for glucose, mannose and fructose are 1, 1.5 and 3 mM, respectively. At least in the case of mannose and fructose, transport seems to be of the non‐active type.
In contrast with vegetative cells, spores of Streptomyces appreciably transport only glucose, with a Km of 1 mM, but not mannose and fructose. This observation can be related to the lag for growth of Streptomyces spores on mannose or fructose with respect to growth on glucose.
Tryptophanyl‐Transfer Ribonucleic‐Acid Synthetase from Beef Pancreas
Authors: Iborra François , Dorizzi Mireille , Labouesse Julie 
Published: March 2005

Binding of tryptophan, tryptamine and ATP to tryptophanyl‐tRNA synthetase was studied by equilibrium dialysis experiments. There are two binding sites per mole of enzyme both for tryptophan and for tryptamine. Ks for tryptophan is 0.95 μM and for tryptamine is 1.8 μM. In the case of ATP no binding could be measured over the range of concentrations examined. The Scatchard plots of tryptophan and tryptamine binding do not shown any cooperativity between the subunits.Dissociation of the dimeric enzyme was studied at very low protein concentration. Upon dilution of the enzyme both the [32P]PPi‐ATP isotope exchange activity and the tRNA charging activity are lost simultaneously. Kinetic evidence demonstrates that the inactivation is primarily due to the dissociation of the active dimer into inactive monomers. The dissociation is strongly promoted by alkaline pH and is inhibited by the presence of tryptophan or tryptophanyladenylate but not by that of tRNA. The dissociation constant of the dimer‐monomer equilibrium at pH 8.5 is 15 nM at 25 °C. The dissociation form is more susceptible to denaturation than the dimeric species.The results reported in the paper suggest that even if there are not binding interactions between the subunits, the active conformation of the enzyme depends on their associated state.
Evolution of Ribosomal Proteins
Authors: Delaunay Jean , Creusot Francine , Schapira Georges 
Published: March 2005

We have studied the evolution of ribosomal proteins over a spectrum of 13 species ranging from man to plants using a two‐dimensional polyacrylamide gel electrophoresis technique. We tried to quantify the proximity of these species by coelectrophoresing the proteins from various combinations of two species. The following tentative conclusions have been reached.

For reptiles and birds which diverged 300 million years ago from the line leading to mammals, ribosomal proteins display the same fingerprints as mammals.
For amphibians and fish which diverged 350–400 and 440–500 million years ago respectively, the fingerprints show limited differences compared with mammals. Those of fish show some diversity within the species.
For lower species (crustaceans, molluscs) and plants, the fingerprints exhibit a great diversity.
The Role of Histidine Residues in Yeast Hexokinase
Authors: Grouselle Michel , Thiam Abdul Aziz , Pudles Julio 
Published: March 2005

Specific acylation of the histidine residues of yeast hexokinase with diethylpyrocarbonate at pH 6.1 or 7.5 leads to a partial and reversible inactivation of the enzyme.The carboethoxylation of the histidine residues at pH 7.5 was faster than at 6.1 and the loss in activity was also higher.However the difference in the amount of inactivation was related to a greater instability of the carboethoxylated enzyme at pH 7.5.When the carboethoxylation was carried out at pH 7.5 and at 0 °C, only the histidines residues were modified (nine residues per enzyme subunit) and still 40% of the activity was left. d‐Glucose protects the enzyme activity in the course of the carboethoxylation at pH 7.5, but has no effect at pH 6.1. However the rate and number of histidines acylated were the same as when the experiments were carried in absence of the substrate.All these results clearly indicate that the histidine residues are not implicated either in the catalytic or in the substrate binding site of yeast hexokinase.This was also confirmed by showing that the 60% inactivated enzyme had the same Km as the native enzyme for both substrates d‐glucose and Mg · ATP. Only v was affected.The inactivation effect of the carboethoxylation was not related to a displacement of the pH optimum of the activity, since the enzymes species having five and eight histidine residues modified‐respectively in absence and presence of d‐glucose at pH 7.5 gave the same pH profile of activity as the native enzyme.Absorption spectroscopy, fluorescence and ultracentrifugation studies have shown that the loss of enzymic activity in the course of the modification of the histidine residues is only related to changes of the protein conformation.
A Small‐Angle X‐Ray Scattering Study on Poly[d(A‐T) · d(A‐T)], Poly[d(A‐s4T) · d(A‐s4T)] and Poly[d(A‐s4U) · d(A‐s4U)]
Authors: Zipper Peter 
Published: March 2005

A small‐angle X‐ray scattering study was performed with solutions of the alternating polydeoxynucleotide poly[d(A‐T) · d(A‐T)] and its analogs poly[d(A‐s4T) · d(A‐s4T)] and poly[d(A‐s4U) · d(A‐s4U)]. At low concentration of NaCl and neutral pH almost identical results were obtained for these polydeoxynucleotides. At small scattering angles the same cross section radius of gyration Rc= 0.92 ± 0.03 nm for all three polydeoxynucleotides was derived from the scattering curves. At larger scattering angles a second cross‐section radius of gyration Rc2 could be determined which amounts to 0.855 ± 0.02 nm for poly[d(A‐T) · d(A‐T)], 0.86 ± 0.01 nm for poly‐[d(A‐s4T) · d(A‐s4T)] and 0.82 ± 0.01 nm for poly[d(A‐s4U) · d(A‐s4U)], respectively. The length per nucleotide pair, 0.33 ± 0.03 nm, was found to be the same for all three polydeoxynucleotides. These results are similar to those for natural DNA.The above results for poly[d(A‐s4T) · d(A‐s4T)] and poly[d(A‐s4U) · d(A‐s4U)] refer to the modification of these polydeoxynucleotides which prevails at low concentrations of 1:1 electrolytes and was designated as helix I. The length per nucleotide pair obtained in this study appears to be consistent with the presence of strong 0 0 8 and 0 0 16 reflections in the high‐humidity X‐ray fibre diffraction patterns for the sodium salt of poy[d(A‐s4T) · d(A‐s4T)]. The values for the cross‐section radii of gyration, on the other hand, seem to be inconsistent with the reversed Hoogsteen base‐pairing scheme proposed for poly[d(A‐s4T) · d(A‐s4T)] and poly[d(A‐s4U) · d(A‐s4U)], because the similarity of these values to those for poly[d(A‐T) · d(A‐T)] and natural DNA is contrary to the results of theoretical calculations on models built up from reversed Hoogsteen base‐pairs. According to these calculations, the cross‐section radius of gyration of poly‐[d(A‐s4T) · d(A‐s4T)] ought to be smaller than that of natural DNA by about 0.16–0.2 nm if this polydeoxynucleotide really were of the reversed Hoogsteen type.
Presence of a Single Essential Histidyl Residue in Octopine Dehydrogenase as Shown by Photooxidation
Authors: Thoméa‐Beau Françoise , Olomucki Anna 
Published: March 2005

Octopine dehydrogenase of Pecten maximus photooxidized in the presence of Rose Bengal was irreversibly inactivated following first‐order kinetics. The coenzyme and its analogues do not protect significantly against the photoinactivation whereas the substrates in the presence of coenzyme give an almost complete protection. About one –SH group was lost in the two cases. Moreover the native enzyme and the enzyme in which three –SH groups (including the essential one) were reversibly substituted were photoinactivated at the same rate. This suggests that the loss of the –SH group does not contribute to the photoinactivation of octopine dehydrogenase.About two histidines were destroyed in the photoinactivated enzyme and only one in the fully protected enzyme. It seems therefore that in octopine dehydrogenase only one histidine is essential and this residue can be protected in the ternary complexes. The partial protection effects of argi‐nine or pyruvate are additive when the two substrates are used together. This fact and the lack of protective effect of the coenzyme suggest that the essential histidine residue is near the substrates binding site.
The Isolation and Properties of Two Prephospholipases A2 from Porcine Pancreas
Authors: Nieuwenhuizen Willem , Steenbergh Paul , de Haas Gerard H. 
Published: March 2005

Prephospholipase A2, when isolated via the procedure described previously, by us in 1968, has pyroglutamic acid as the N‐terminal amino acid. However, this could be an artifact due to the drastic conditions of one of the early stages of the purification. Therefore a milder procedure has been developed in order to check whether or not pyroglutamic acid is artifactual. During these experiments two forms of prephospholipase A2 were purified: one (form II) being identical with the one already described, the other (form I) having a shorter activation peptide, i.e. Ser‐Ser‐Arg instead of <Glu‐Glu‐Gly‐Ile‐Ser‐Ser‐Arg.Evidence is given that this is the only difference between forms II and I and that elastase can be responsible for the specific conversion of form II to form I by release of the N‐terminal tetra‐peptide of form II.No carbohydrates could be detected in any of the preparations.
Studies on the Inhibition of the L‐Serine O‐Sulphate‐Degrading System of Pig Liver and the Topography of Its Active Site
Authors: Tudball Norman , Thomas Peter 
Published: March 2005

The inhibition of the l‐serine O‐sulphate‐degrading activity of pig liver has been investigated. compounds that acted as competitive inhibitors all possessed the basic stereochemistry associated with the l‐serine O‐sulphate molecule.
In general the most efficient competitive inhibitors were those possessing an interproton distance of 0.75 nm, with two electronegative ends or alternatively one electronegative end and the negative end of a dipole.
O‐Phospho‐l‐serine is an atypical inhibitor since it obeys non‐competitive inhibitor kinetics even though from theoretical considerations it should act as a competitive inhibitor.
3‐Chloro‐l‐alanine methyl ester is a substrate for the enzyme.
4‐Iodoacetamidosalicylic acid acts as an irreversible inhibitor of the system.
The probable topography of the active site and the disposition of the substrate at the active site is discussed.
Transfert du mannose, à partir de GDP‐mannose, à des accepteurs lipidiques chez Aspergillus niger
Authors: Létoublon Robert C. P. , Comte Jane , Got René 
Published: March 2005

Microsomal preparations from Aspergillus niger mediate transfer of mannosyl units from GDP‐mannose to endogenous lipids. Mannosyltransferases require divalent cations for activity. Optimum pH, temperature maximal activity and optimal metal ion concentration are different whether Mn2+ or Mg2+ are used. K
m value for GDP‐mannose is 0.2 μM in presence of Mg2+, while, with Mn2+, two values are obtained: 0.2 μM and 10 μM for low and high‐substrate concentration.The lipid acceptor is purified by fractionation of the lipid extract on silicic‐acid column followed by thin‐layer chromatography on silica gel.Chromatographic properties, presence of phosphorus, coloration with the anisaldehyde reagent and acid lability of the lipid suggest that this compound is a polyprenol‐phosphate.
The Substrate Specificity of Pantethinase
Authors: Duprè Silvestro , Rosei Maria Anna , Bellussi Luisa , Del Grosso Elena , Cavallini Doriano 
Published: March 2005

The substrate specificty of pantethinase, the mammalian enzyme which has been isolated from horse kidney cortex, has been studied. The real substrate has been found to be pantetheine in the reduced form, and the involvement of one or more—SH groups of the enzyme is also considered.A number of other compounds, chemically related to pantetheine, has also been tested as substrates. Pantethinase is able to metabolise pantetheine‐4′‐phosphate, with an activity about 10% of that exhibited for pantetheine; it is inactive on the other substances tested (pantothenoyl‐cysteine‐4′‐phosphate, pantothenoylcysteine, pantetheine thiazoline, CoA).The metabolic role of pantethinase seems to be, in the light of the above results, connected with a degradative pathway of pantetheine‐4′‐phosphate, which is known to be one of the intermediates in the biosynthesis of CoA.
Purification and Properties of a Coupling Factor (Ca2+‐Dependent Adenosine Triphosphatase) from Rhodospirillum rubrum
Authors: Johansson Bo C. , Baltscheffsky Margareta , Baltscheffsky Herrick , Baccarini‐Melandri Assunta , Melandri Bruno A. 
Published: March 2005

A coupling factor has been purified from an acetone powder extract of Rhodospirillum rubrum chromatophores. This restores to decoupled chromatophores (extracted with respect to coupling factor) both photophosphorylation and Mg2+‐dependent ATPase activities. The coupling factor had been partially purified by gel filtration through a Sepharose 6B column, and further purified by ultra‐filtration and sucrose‐density‐gradient centrifugation. At each stage of purification, the coupling factor activity was coincident with a Ca2+‐dependent ATPase activity, increasing in total activity during the purification. Mg2+, Mn2+, Co2+ or Zn2+ could not substitute for Ca2+ in activation of this soluble ATPase, but these four metals strongly inhibited the activity of the Ca2+‐dependent ATPase.
By incubation with decoupled chromatophores, the soluble Ca2+‐dependent ATPase was rebound to the membrane in the presence of either Mg2+ or Ca2+. This binding resulted in a partial masking of the Ca2+‐dependent ATPase activity of the soluble enzyme.
The purified ATPase has a Km value of 1.2 mM for ATP. The Ki values for inhibition of the soluble Ca2+‐dependent ATPase by Mg2+ (170 μM), and by ADP (42 μM) are in close agreement with the corresponding Km values for Mg2+‐dependent ATPase and photophosphorylation, respectively, as measured with chromatophores.
The membrane‐bound Mg2+‐ or Ca2+‐dependent ATPase activities were inhibited by oligomycin. Azide and parahydroxymercuribenzoate inhibited both the soluble and the membrane‐bound ATPase activities. Treatment with phospholipase A inhibited both the membrane‐bound ATPase, but had no effect on the soluble Ca2+‐dependent ATPase.
The sedimentation constant at 1 mg protein/ml of the extensively purified coupling factor is s20, w= 13.1 × 10−13 s, and the approximate molecular weight 350000.
Effects of Deoxyribonucleases I and II on Rat‐Liver‐Chromatin Transcription in vitro
Authors: Pays Etienne , Ronsse Annie 
Published: March 2005

The hydrolysis by DNAase I or II of DNA in chromatin remains limited even after prolonged incubation.
This limitation might be due to a redistribution under the action of DNAase of f l histone
With large amounts of DNAase, all of the chromatin DNA may however be digested.
A comparison is made between the extent of DNA hydrolysis by DNAase and the resulting inhibition of chromatin template activity for endogenous, Escherichia coli or rat liver (form II) RNA polymerases. Our results are not in favour of a greater sensitivity to DNAase for the euchromatic sequences than for the repressed ones. prolonged incubation. on chromatin DNA.
Further Investigations of the Specificity of an Acid Deoxyribonuclease from Helix aspersa (Müll.)
Authors: Devillers‐Thiery Anne , Bernardi Giorgio , Ehrlich Stanislav D. 
Published: March 2005

Linear relationships were found to hold between the percentages of the 3′‐P terminal and 5′‐OH terminal and penultimate nucleotides released by snail acid DNAase from bacterial DNAs and the (dG + dC) contents of the latter. This finding is similar to previous results obtained on spleen acid DNAase; as in the case of this enzyme, the composition of the termini released by the snail DNAase from calf thymus DNA devite from the linear relationships mentioned above.The snail enzyme appears to recognize a sequence of at least two nucleotides, namely those which will be released as 3′‐P and 5′‐OH terminlas, respectively.
Fluorescence Study of Liver‐Alcohol‐Dehydrogenase Complexes with Berberine and Other Ligands
Authors: Kovář Jan , Skurský Ladislav 
Published: March 2005

The dissociation constant of the enzyme · berberine complex has been determined by various fluorescence titration methods. The good agreement of the dissociation constants supplied by the titration of the complex by NADH, o‐phenanthroline, pelargonic and capric acids gives additional support for the previously made assumption that berberine binds to the active centre of the enzyme.The lipophilic character of both partners is essential for the ability to bind. Nevertheless other results support the view that more specific interactions, possibly with the Zn atom and the –SH groups, are involved also.A preliminary judgement about steric factors of the studied interaction is supplied by the ability of adenosine diphosphate‐ribose to form a ternary complex with the enzyme and berberine. Also NAD itself, although competing with berberine in lower concentrations, seems to form a ternary complex at high NAD concentrations. Both pyrazole and ethnol compete with berberine. The corresponding fluorescence titrations of the enzyme · berberine complex enable us to evaluate the dissociation constants of the binary complexes of the enzyme with pyrazole and alcohol.Attempts have been done to measure the denaturation rates of the enzyme in acid media by following the disappearance of the fluorescent enzyme · berberine complex.
Lipid Requirement of Membrane‐Bound ATPase
Authors: Roelofsen Ben , van Deenen Laurens L. M. 
Published: March 2005

The (Na++ K+)‐stimulated ATPase of human erythrocyte ghosts is completely inactivated by treatment with pure phospholipase A2 or phospholipase C.
These phospholipases also cause considerable or even complete loss of Mg2+‐dependent ATPase activity.
Enzymatic hydrolysis of sphingomyelin does not significantly influence either of the ATPase activities.
Conversion of the glycero‐phospholipids into phosphatidic acid by phospholipase D causes a drastic decrease in the Mg2+‐dependent ATPase activity, whereas the (Na++ K+)‐stimulated activity is increased.
Enzymatic decarboxylation of the phosphatidylserine fraction of the ghosts does not influence the (Na++ K+)‐stimulated ATPase, unless the last 13% of this fraction is converted into phosphatidyethanolamine, when there is a complete loss of this particular ATPase activity. On the other hand, the Mg2+‐dependent activity tends to be increased by this treatment.
The (Na++ K+)‐stimulated ATPase activity of erythrocyte ghosts treated with phospholipase C and subsequently extracted with dry ether, can be completely reconstituted by the addition of phosphatidylserine. Phosphatidylcholine, phosphatidylethanolamine and phospholipid mixtures are found to be ineffective. Phosphatidic acid produced a partial restoration of activity.
It is concluded that the (Na++ K+)‐stimulated ATPase activity strongly depends upon the presence of phosphatidylserine, of which only a minor fraction in the erythrocyte membrane is directly involved. It cannot be concluded from the experiments described in this paper that the Mg2+‐dependent ATPase also requires a specific phospholipid. However, a direct involvement of either cholesterol or sphingomyelin in this activity can be precluded.
The Anatomy of the Mitochondrial DNA
Authors: Porcher Harald H. , Koch Jürgen 
Published: March 2005

The distribution of the mitochondrial DNA among the allomorphic forms, supercoiled circle, open circle and linear rod is a characteristic feature of each cell line. After pulse‐chase labeling with [Me‐3H]thymidine the bulk of the radioactivity can be located either in the supercoiled circular mitochondrial DNA (monkey Vero, ATCC; CCL 81) or in the open circular mitochondrial DNA (mouse NCTC 929, ATCC; CCL 1).The open circular mitochondrial DNA from Vero cells contains one single nick, which is located in the heavy strand (alkaline CsCl gradient). In contrast, the open circular mitochondrial DNA from mouse cells contains one nick in one strand and at least two nicks in the opposite strand.The bulk of the supercoiled Vero mitochondrial DNA has a heat‐labile site in the heavy strand and one site in both strands at which the phosphodiester backbone can be hydrolyzed by pancreatic RNAase.