bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nucleotide Sequences from Specific Areas of the 16S and 23S Ribosomal RNAs of E. coli
Authors: Fellner P. 
Published: March 2005

The primary structures of the 16S and 23S ribosomal RNAs of Escherichia coli have been studied. Nucleotide sequences have been determined which occur in specific areas close to the small numbers of methylated nucleotides which are present in these molecules. Fragments containing these methylated nucleotides were obtained by digestion of radioactive RNA substrates with T1 ribonuclease. Such digestion products were fractionated by high‐voltage electrophoresis in two dimensions.The 23S RNA yielded predominantly 11 methylated oligonucleotides on digestion, and the 16S RNA gave rise to 6 methylated components. Nucleotide sequence analysis of these products was carried out, and the nature of the modified nucleotides occurring in each product was also examined. It was found that some of the sequences contained several modified components positioned close to each other. Quantitative studies indicate that each of the methylated sequences is probably present twice in a molecule of the 23S RNA, so that these sequences encompass about 5% of the nucleotides present in the entire molecule. It is postulated that extensive repetition of nucleotide sequences occurs within the 23S RNA.
Heterogeneity of Erythrocyte Catalase
Authors: Mörikofer‐Zwez S. , Cantz M. , Kaufmann H. , von Wartburg J. P. , Aebi H. 
Published: March 2005

Human and horse erythrocyte catalase is separated into three fractions (A, B and C) upon chromatography on DEAE‐cellulose. Fractions B and C are formed out of fraction A by oxidation of sulfhydryl groups during preparation.
A purification method, including chromatographies on DEAE‐ and CM‐cellulose was devised. The whole procedure was carried out under nitrogen and in presence of EDTA, yielding the pure native enzyme (fraction A).
Both the human and horse enzyme contain 16 cysteine residues per molecule, determined by titration with p‐chloromercuribenzoate and amino acid analysis of the fully carboxymethylated or the performic acid oxidized protein.
The transition of the chromatographic fraction A to fraction C is characterized either by a conformational change or by an irreversible oxidation of sulfhydryl groups to higher oxidation products.
Yeast Alcohol Dehydrogenase: –SH Groups, Disulfide Groups, Quaternary Structure, and Reactivation by Reductive Cleavage of Disulfide Groups
Authors: Bühner M. , Sund H. 
Published: March 2005

Storage of yeast alcohol dehydrogenase in crystal suspension causes a decrease of the enzymatic activity which is strongly related to the number of free –SH groups. With a rate slower than the rate of inactivation the enzyme molecule (molecular weight reinvestigated from hydrodynamic measurements to be 141000) dissociates into four polypeptide chains (molecular weight 35000) which are enzymatically inactive. By sulfitolysis in 4 M urea and amperometric titration it was shown that free –SH groups are oxidized mainly to disulfide groups during inactivation.The formation of disulfide bonds does not occur between –SH groups of different polypeptide chains. It is assumed that the inactivation process from the fully active enzyme molecule to the inactive polypeptide chains is not an all‐or‐none process but passes through three stages: 141000 (fully active) → 141000 (partially active) → 141000 (inactive) → 4 → 35000 (inactive). The more inactive the alcohol dehydrogenase, the more sensitive it is to heat denaturation and peptidase attack.By treatment with mercaptoethanol or Cleland's reagent the disulfide bonds could be reduced and the enzymatic activity was recovered partially. The undissociated inactive molecules could be fully reactivated. With one of the investigated enzyme preparations which contains a peptidase it was also possible to reactivate and reassociate alcohol dehydrogenase from the polypeptide chains.
Elektronenspinresonanz‐Untersuchungen an Hämin‐Mercaptan‐Komplexen
Authors: Röder A. , Bayer E. 
Published: March 2005

The oxidized cytochrome P‐450 shows an ESR‐spectrum with g‐values at 2.41, 2.26 and 1.91.An attempt has been made to simulate these properties by studying the products of the reaction of a series of thiols with heminechloride in various solvents. g‐values have been obtained around g3= 2.4, g2= 22 and g1= 1.9, depending on the chemical nature of the thiol and the solvent.The structure of the heme site in the oxidized cytochrome is discussed.
18O‐Studies with Citrate Synthase and Malate Synthase
Authors: Wunderwald P. , Eggerer H. 
Published: March 2005

The labelling pattern of a β‐hydroxyacid, synthesized on nucleophilic enzymatic reaction of acetyl‐CoA with an α‐oxoacid in H218O, yields information about the mechanism of this type of enzyme action. Two related reactions catalyzed by citrate synthase and malate synthase were investigated in H218O. Malate was formed as the product in both cases.
A micro‐scale procedure is described for the stepwise and specific removal of the oxygen groups present in malate, by enzymatic degradation.
Mass spectrometric analyses of the enzymatically obtained 18O‐labelled malates and of their degradation products revealed the labelling of one oxygen atom of one carboxyl group of malate. The significance of this result is discussed.
Ribonucleotide Reductase from Regenerating Rat Liver
Authors: Larsson A. 
Published: March 2005

Ribonucleotide reductase was purified 150‐fold from crude extracts of 48 hour regnerating rat liver using centrifugation at 100 000 ×g, pH 5 precipitation, ammonium sulfate fractionation, and Cγ‐alumina adsorption. The enzyme activity was assayed by the conversion of [3H]cytidine nucleotides to deoxycytidine nucleotides. For optimal activity the enzyme required addition of ATP, Mg ions, Fe ions, and a dithiol reducing agent.Ribonucleotide reductase could be demonstrated in crude extracts of regenerating livers but not in livers of normal or sham operated rats. After purification, however, all three types of livers were found to contain the enzyme, regenerating livers having the highest levels. After partial hepatectomy ribonucleotide reductase activity increased approximately 20‐fold with a maximum at 50 hours after operation. Within the next 50 hours the enzyme levels decreased to those of normal liver tissue.
Relative Proportions of Mitochondrial and Nuclear DNA in Yeast under Various Conditions of Growth
Authors: Fukuhara H. 
Published: March 2005

The relative proportions of mitochondrial and nuclear DNA were compared between various types of cells including anaerobically grown cells, aerobically grown glucose‐repressed and highly derepressed cells. The comparison was made by the use of a labelled reference yeast, which was mixed with various types of cells before extraction of DNA, so that the results could not be influenced by any unequal losses of DNA components during extraction.Relative proportions of mitochondrial DNA and nuclear DNA were estimated from the specific radioactivities of the two DNA components which were separated by column chromatography on hydroxyapatite.Contrary to the previous observation by other authors, no major differences were found between completely derepressed cells grown aerobically on galactose up to the stationary phase and cells grown on high glucose under strict anaerobiosis or cells growing under strong aerobic glucose repression.By the same technique, the mitochondrial DNA content of some other strains including a δ– mutant was examined.
Oxidative Phosphorylation and Compartmentation of Fatty Acid Metabolism in Brown Fat Mitochondria
Authors: Hittelman K. J. , Lindberg O. , Cannon B. 
Published: March 2005

Mitochondria freshly isolated from brown adipose tissue by a standard procedure consistently fail to display normal oxidative phosphorylation. Incubation of these particles with ATP and carnitine in the absence of exogenous substrate results in a rapid burst of respiration which eventually slows to a low resting rate. Oxidation of the endogenous substrate is absolutely dependent upon the presence of both ATP and carnitine and is completely inhibited by rotenone. In the absence of added CoASH, respiration is also inhibited by atractyloside, and this inhibition in completely released by addition of CoASH.
After the ATP + carnitine‐induced respiration has slowed to a low resting rate, oxidative phosphorylation is observed during the oxidation of added α‐ketoglutarate, succinate, or α‐glycerophosphate.
If the mitochondria are incubated with ATP and carnitine in the presence of rotenone, coupled behavior is also observed upon subsequent oxidation of succinate or α‐glycerophosphate.
Under appropriate conditions, the time‐course of appearance of oxidative phosphorylation corresponds closely to the time‐course of appearance of significant levels of acylcarnitine.
It is concluded that the endogenous substrate of brown fat mitochondria is free fatty acids which lie initially outside the acyl‐CoA barrier, and that these are responsible for the uncoupled behavior of the freshly isolated particles. By providing the mitochondria with the appropriate components for activation and transport of free fatty acids, the redistribution which occurs relieves the uncoupling and hence both oxidative phosphorylation and classical sensitivities to inhibitors become evident.
The significance of the fatty acid transport mechanism in these mitochondria is discussed with respect to a possible role in regulating the degree of uncoupling which may occur during active thermogenesis by brown adipose tissue.
Brain Lipid Analysis of a Myelin Deficient Mutant, the “Quaking” Mouse
Authors: Jacque C. M. , Harpin M. L. , Baumann N. A. 
Published: March 2005

The “Quaking” mouse is a mutant which has an inherited disease involving the process of myelination in the central nervous system.Fractionation of brain lipids and fatty acid methyl ester analysis of each lipid isolated have been performed. No qualitative abnormalities have been detected, either in ethanolamine, serine and choline phosphoglycerides, or in cholesterol. Proof has now been obtained that the considerable reduction in long chain fatty acids (C24), occurs in cerebrosides, sulphatides (where they are normally major constituents) and in sphingomyelin. Long chain hydroxylated fatty acids are comparatively less diminished than non‐hydroxylated one. This metabolic defect, detected in all the sphingolipids that contain this type of fatty acids could be in favour of a mutation related to fatty acid elongation which is very important at the time of myelin formation.
Biosynthesis of Salmonella Lipopolysaccharide. The in vitro Transfer of Phosphate to the Heptose Moiety of the Core
Authors: Mühlradt P. 
Published: March 2005

An enzyme involved in the biosynthesis of the core part of Salmonella lipopolysaccharide, an ATP‐dependant lipopolysaccharide phosphorylating enzyme, has been studied in an in vitro system. The system requires as acceptor the heated 20 000 ×g cell wall fraction from Salmonella minnesota mR5, a mutant which lacks the phosphotransferase (P–), and as enzyme source 1000 00 ×g supernatant of protein extracts from rough P+ mutants of either S. minnesota or S. typhimurium. Phosphate donor is ATP labelled with 32P in the γ‐position. The enzyme system requires a high concentration of Mg++ ions (0.1 M) for optimal functioning.The phosphotransferase is solubilised by repeated washings of cell debris obtained after lysis of the cells by EDTA and lysozyme with dilute Tris buffer.Isolation and characterisation of two fractions consisting of heptose phosphate from the lipopolysaccharide of S. minnesota mRz, a UDP‐synthetase‐less P+ mutant, is described. Products of partial hydrolysis of acceptor after 32P‐incorporation were compared with these fractions and found to be identical. In this way the incorporation product was identified to be core‐lipopolysaccharide (glycolipid) which is phosphorylated at the heptose moiety.
Structure covalente de la myoglobine de cheval
Authors: Dautrevaux M. , Boulanger Y. , Han K. , Biserte G. 
Published: March 2005

The complete sequence (153 amino acids) of horse heart myoglobin has been established.The sequence of a peptide isolated from chymotrypsin hydrolyzates of globin allowed to fill a gap in the tentative sequence previously proposed; this peptide was studied by means of pepsin hydrolysis, action of N‐bromosuccinimide on histidyl bonds, and Edman degradation method associated with dansylation.After hydrolysis of globin by chymotrypsin treated by TLCK, the same major peptides were found as after hydrolysis by non‐treated chymotrypsin. These peptides were identified by ion‐exchange resins and bidimensional paper chromatography, and also by the determination of their amino‐acid composition.The suppression of secondary cuts explains the presence of new peptides, whose the composition and N‐terminal sequences were determined. It was then possible to confirm several sequences which could be previously deduced from the study of split products after cyanogen bromide treatment. The specificity of chymotrypsin towards certain types of peptide bonds is discussed.Horse myoglobin, as compared with sperm whale myoglobin, contains 18 differences: 17 substitutions and one inversion. The major part of the substitutions are located in N‐ and C‐terminal sequences; they are all punctiform, resulting from the replacement of only one base in each codon.
Pyruvate Formate‐Lyase Reaction in Escherichia coli
Authors: Knappe J. , Schacht J. , Möckel W. , Höpner Th. , Vetter H. , Edenharder R. 
Published: March 2005

Fractionation of the cell extract led to partial isolation of four protein fractions that are involved in the dissimilation of pyruvate into acetyl‐CoA and formate: Enzyme I, molecular weight about 140000; enzyme II, molecular weight about 30000, which requires an activation by ferrous ion and dithiols; enzyme III, molecular weight 25000, which is a flavorprotein with flavin‐monoucleotide as coenzyme; and a hitherto less characterized fraction IV. The system in addition comprises the cofactors S‐adenosylmethionine and thiamine diphosphate.Enzyme III, fraction IV, and thiamine diphosphate could be replaced by the reagents cobaltous ion and thiols which form complexes of high reducing power. This part of the enzyme system obviously plays an auxiliary role, most likely by providing an appropriate redox potential via pyruvate as electron donor.The ability to dissimilate pyruvate was found to arise only and specifically from an interaction between enzyme I, ferrous ion‐activated enzyme II and adenosylmethionine, in presence of either of the above auxiliary systems. Enzyme I is thereby converted into an active form, possibly by reduction, which alone is responsible for the catalysis of the pyruvate dissimilation reaction. The identification of this pyruvate formate‐lyase was accomplished by sedimentation experiments in anaerobic sucrose gradients.
On the Duplication of Ribosomal RNA Cistrons in Chinese Hamster Cells
Authors: Amaldi F. , Giacomoni D. , Zito‐Bignami R. 
Published: March 2005

Because of the redundancy of ribosomal RNA cistrons and in analogy with a few known special cases, one may postulate that a few “master genes” for rRNA direct the synthesis of multiple copies of themselves per cell cycle. We have shown that in Chinese hamster cells rRNA cistrons duplicate like the bulk of DNA, once in a cell cycle. The time during the S‐phase at which rRNA genes duplicate has also been determined by means of RNA‐DNA hybridization studies.The time of duplication of rRNA genes occurs between t= 1.5 and t= 3.0 hours from the beginning of the S‐phase.
The dAMP‐Ag+ Complex and the Solubilization of Benzo[a]pyrene
Authors: Green B. , Homer R. B. , Mcdonough G. R. 
Published: March 2005

The solubilization of the polycyclic hydrocarbon benzo[a]pyrene by aqueous solutions of dAMP‐Ag+ complexes has been investigated. At high pH solubilization is efficient at Ag+/dAMP ratios not more than 1 but is markedly diminished when the ratio of total silver ions added per base residue is greater than 2. The components separately show little solubilizing activity.The ultraviolet absorption and circular dichroism spectra of silver complexes of dAMP and poly A under various conditions have been compared.
Intracellular Localization of Phosphodiesterases I and II in Rat Liver
Authors: Erecińska Maria , Sierakowska Halina , Shugar David 
Published: March 2005

Differential and density gradient centrifugation techniques have been employed to study the intracellular distribution of phosphodiesterases I and II in rat liver, using as specific substrates the p‐nitrophenyl esters of thymidine‐5′‐phosphate and thymidine‐3′‐phosphate. Some of the results for phosphodiesterase I were also examined with the use of a 5′‐terminated DNA core as substrate.Phosphodiesterase I was found to be largely (>80%) localized in the plasma membrane, whereas purified nuclei, rough microsomes, and the inner mitochondrial membrane are essentially free of this enzyme. The possible sources of apparent phosphodiesterase I activity of the outer mitochondrial membrane, the lysosomes and the smooth microsomal membrane are discussed.Phosphodiesterase II is localized largely in the soluble fraction of the lysosomes, and exhibits the latency typical of lysosomal hydrolases.The overall findings are examined in relation to those of other investigators. Possible reservations regarding the absolute specificities of the substrates employed, and their bearing on the localization results, are discussed.
Enzymic Flux Rates within the Mononucleotides of the Mouse Liver
Authors: Zahn D. , Klinger R. , Frunder H. 
Published: March 2005

Within the first 30 sec after intravenous injection of [32P]Pi the P‐flux was measured within the mononucleotide pool of the normal mouse liver. It is only in this short time interval that the dynamic phase of tracer kinetics is met, permitting proper calculations of flux rates of the mononucleotides with high turnover.The simplified model applied for the calculation of the stated flux rates describes fairly adequately the main pathways within the complex network of possible mononucleotide interconversions.The P‐flux from the β‐P of ADP to the β‐P of ATP, catalyzed preferentially by oxidative and substrate phosphorylation amounts to 33 μmoles per g fresh liver per min.12, 0.7, 0.3 and 0.01 μmoles γ‐P of ATP are transfered per g per min to the β‐P of ADP, UDP, GDP and CDP, respectively, via the group nucleoside monophosphate kinases. These flux rates are 1–2 orders of magnitude less than expected from the kinetics behaviour of the involved enzymes in vitro. The reverse reaction of the nucleoside monophosphate kinases is probably small.9, 4 and 0.5 μmoles of the γ‐P of ATP are transferred per g per min to the γ‐P of GTP, UTP and CTP via nucleoside diphosphate kinase.
Studies on the Bacteriophage MS2
Authors: Vandenberghe A. , van Styvendaele B. , Fiers W. 
Published: March 2005

Undegraded, uniformly 32P‐labelled replicative form and replicative intermediate were prepared and fractionated according to sedimentation rate.

For each fraction the amount of 5′‐terminal residues, which after alkaline hydrolysis are released as 5′‐triphosphoryl, 3′(2′)‐phosphoryl nucleosides (nucleoside tetraphosphates), was quantitatively determined. The replicative form contained O, and the replicative intermediate 2.5 nascent chains, if the assumption is made that the latter are on the average half completed. The number of nascent chains apparently increases with increasing sedimentation constant of the replicative intermediate molecules.
The nucleoside tetraphosphate, released from each fraction, was identified as exclusively pppGp. This is interpreted as evidence for a 5′ to 3′ polarity in the synthesis of viral RNA, i.e. a growing 3′OH end.
The replicative form and replicative intermediate were also prepared from cells, in which the 32P‐label was chased for 5 min before harvest. The amount of nucleoside tetraphosphate released agreed with a single end group per complete chain. Presumably 50 to 100% of the residual labelled terminal was derived from the complementary strand, and again only pppGp was found. It follows that the 3′‐terminal adenosine residue of the viral RNA is presumably not part of the genetic information transferred during replication.
Relationship between Age and Properties of Human and Rabbit Erythrocyte Glucose‐6‐Phosphate Dehydrogenase
Authors: Fornaini G. , Leoncini G. , Segni P. , Calabria G. A. , Dacha M. 
Published: March 2005

The properties of human and rabbit erythrocyte glucose‐6‐phosphate dehydrogenase have been investigated during aging in vivo. The erythrocytes of different age have been prepared by 2 procedures: (a) by inducing a reticulocytosis by phenylhydrazine administration to rabbits and (b) by separating the young and old red cells of man and rabbit according to the different resistence to osmotic lysis.During aging, human and rabbit glucose‐6‐phosphate dehydrogenase shows a decrease of the catalytic activity and some marked modifications of its properties. Thermolability and NADPase‐dependent inactivation increase; the protective effect of NADP and the affinity for both glucose‐6‐phosphate and NADP substrates are decreased; no modifications have been demonstrated as regards pH optimum and electrophoretic patterns in starch gel. It is possible that these modifications begin after the expulsion of ribosome material.According to the literature concerning the behaviour of other enzymes in the physiological state and of glucose‐6‐phosphate dehydrogenase of some pathological conditions, it is possible that the modified properties of the enzyme during aging in vivo can be related to some structural modifications of the protein.
The Reversible Removal of one Specific Copper(II) from Fungal Laccase
Authors: Malkin R. , Malmström B. G. , Vänngård T. 
Published: March 2005

One of the four copper atoms of fungal laccase forms a Cu1+‐chelate with bathocuproine disulfonate at pH 4.0 in 1 M guanidine hydrochloride and in the presence of excess ascorbate.
Electron paramagnetic resonance (EPR) analysis of the native and copper‐depleted proteins has shown that one of the two Cu2+ in the protein has been removed under these conditions. The Cu2+ removed has been identified as the Type 2 or “non‐blue” Cu2+. The spectral characteristics of the other Cu2+ present in the molecule (the Type 1 Cu2+) appear unchanged after removal of the second Cu2+.
The copper‐depleted protein is almost completely devoid of enzymic activity after removal of the Type 2 Cu2+ but both the activity and original copper content can be restored after incubation of the copper‐depleted protein with Cu2+ and ascorbate under anaerobic conditions. No activity is restored by the addition of Cu2+ alone.
The rate of removal of the Type 2 Cu2+ closely parallels the rate of decrease of enzymic activity of the protein during the reaction with the chelating agent. These results show that the Type 2 Cu2+ is an integral part of the laccase molecule and has a functional role in the catalytic reaction.
Partial Purification and some Properties of the (R)‐Citrate Synthase from Clostridium acidi‐urici
Authors: Gottschalk G. 
Published: March 2005

The enzyme (R)‐citrate synthase which catalyzes essentially the same biochemical reaction as the citrate synthase but differs in its stereospecificity, has been studied. From cell‐free extracts of Clostridium acidi‐urici the enzyme has been purified 80‐fold by isoelectric precipitation and by chromatography on DEAE‐cellulose and DEAE‐Sephadex. The purification is made difficult by the instability of the enzyme. With the aid of the stereospecific cleavage of citrate by citrate lyase it was demonstrated that the purified (R)‐citrate synthase is not contaminated by the usual citrate synthase.The (R)‐citrate synthase differs in some properties from the usual citrate synthase: it is inactivated by exposure to oxygen, anaerobic conditions and a sulfhydryl compound being required for maximum activity. (R)‐citrate synthase has a specific requirement for manganese ions, the enzyme is inhibited by EDTA, and this inhibition can be reversed by manganese ions but not by magnesium ions.