bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Action Pattern of Amylomaltase from Escherichia coli
Authors: PALMER T. Norman , RYMAN Brenda E. , WHELAN W. J. 
Published: March 2005

Amylomaltase, the inducible 4‐α‐glucanotransferase of Escherichia coli strain ML, has been purified to homogeneity. Its specific activity with a commercial maltose substrate was 500 mkat/kg protein (30 μmol glucose formed min−1 mg protein−1). The purified enzyme, dependent on buffer concentration, exists in interconvertible low‐molecular‐weight (apparent molecular weight 71000) and high‐molecular‐weight (apparent molecular weight 370000) forms.The specificity of amylomaltase has been redefined. Hitherto, the enzyme was thought to be a glucosyltransferase, catalysing the transfer of single glucosyl units, and maltose has been regarded as its most important substrate. Amylomaltase is now shown to exhibit both glucosyl‐transfer and 4‐α‐glucanosyl‐transfer specificity. 4‐α‐Glucanosyl chains containing up to at least nine glucosyl units can be transferred. However, it is concluded that the transfer reaction by which amylomaltase action was originally expressed, does not take place, i.e.Maltose + maltose? Maltotriose + glucoseand that maltose has a restricted role as a substrate. This may be due to the inability of maltose to function as a donor substrate, serving only as an acceptor substrate. It is confirmed that when a maltodextrin serves as a donor, that portion of the molecule transfered by the enzyme is that containing the nonreducing‐end‐group.Enzyme action on chromatographically pure maltose is characterized by a lag phase in the time course of glucose release. The lag phase is overcome by addition of ‘priming’ (catalytic) concentrations of maltotriose or higher maltodextrins. An autocatalytic reaction mechanism involving the generation of primer molecules is proposed to explain the action of the enzyme on maltose.The redefined action pattern of amylomaltase is consistent with the redefined role of the enzyme in the utilization of exogenous and endogenous 1,4‐α‐glucans by E. coli.
Substrate Specificity of the Ultraviolet‐Endonuclease from Micrococcus luteus
Authors: TOMILIN Nikolai V. , PAVELTCHUK Elena B. , MOSEVITSKAYA Tatyana V. 
Published: March 2005

The ultraviolet‐endonuclease isolated from Micrococcus Iuteus, specific for pyrimidine dimers, is able to attack not only ultraviolet‐irradiated DNA (leading to 3′OH‐5′PO4 single‐strand breaks) but also superhelical covalently‐closed circular DNA of phage λ damaged by heating at 70°C, pH 5.93.The number of endonuclease‐sensitive defects in the DNA corresponds to the number of alkailabile bonds (apurinic sites) induced by heating. Competition between ultraviolet‐induced lesions and apurinic, sites for ultraviolet‐endonuclease is demonstrated; the affinity of the enzyme for pyrimidine dimers is about three times that for apurinic sites. Both activities of the ultraviolet‐endonuclease are inactivated at 50 °C at the same rate.The ultraviolet‐endonuclease is able to reduce the infectious activity of depurinated λ DNA towards Ca2+‐treated uvr+ and uvr A Escherichia coli cells.
Basic Charges on Mammalian R bonuclease Molecules and the Ability to Attack Double‐Stranded. RNA
Authors: LIBONATI Massimo , FURIA Adriana , BEINTEMA Jaap J. 
Published: March 2005

A ribonuclease recently isolated from the pancreas of the lesser rorqual or pike whale (Ba1aenoptera acutorostrata), definitely more basic than bovine ribonuclease A, degrades very efficiently double‐stranded RNA under conditions where the action of bovine pancreatic ribonuclease is minimal.On the contrary, a ribonuclease from the pancreas of reindeer, definitely less basic than bovine ribonuclease A, is also, significantly less active than the bovine enzyme at degrading the doublehelical RNA.Two ribonucleases (from the pancreas of guinea pig, the A component, and red deer), with a net charge and a number of basic amino acids similar to those of bovine pancreatic ribonuclease, show an activity on double‐stranded RNA which is indistinguishable from that of bovine ribonuclease A.Finally, a ribonuclease from the pancreas of rat, having a net charge equal to that of bovine ribonuclease A, but three basic residues more than the latter enzyme, shows a modest activity towards the double‐helical RNA.These results are compatible with the idea that the action on secondary structures of RNA by ribonucleases non‐specific for double‐stranded RNA may be related to the number (and possibly the position) of basic charges on the protein molecules.
The Amino‐Acid Sequence of a Fragment of Human‐Serum Albumin Containing Two of Its Antigenic Determinants
Authors: WALKER John E. 
Published: March 2005

The amino acid sequence of a fragment of human serum albumin (inhibitor), which contains two of the antigenic determinants of this protein, is described. It contains 90 amino acid residues and is derived from the carboxyl‐terminal region of human serum albumin.
From this sequence the sequence of a smaller fragment (F1), which has previously been shown to contain one antigenic determinant, has been deduced.
CO2 Reduction to Formate by NADH Catalysed by Formate Dehydrogenase from Pseudomonas oxalaticus
Authors: RUSCHING Ulrich , MÜLLER Ulrich , WILLNOW Peter , HÖPNER Thomas 
Published: March 2005

The direct reduction of CO2 to formate is catalysed by formate: NAD oxidoreductase in the presence of substrate amounts of NADH Proof for this reaction is supplied by the detection of a CO2‐dependent NADH oxidation, and by the identification of [14C]carbonate.The enzyme‐catalysed CO2 reduction by NADH attains the equilibrium predicted by thermodynamic consideration a state which is also reached from the formate side. The Michaelis constant for CO2 is about 40 mM indicating the low affinity of the enzyme for this substrate. The corresponding value for formate is 0.1 mM. Under the special conditions employed the enzyme catalyses the formate oxidation about 30 times faster than the CO2 reduction. That CO2 and not HCO3 is the active species in the reduction was shown by comparing the pH dependency of the velocities of the forward and back reactions and by observing the kinetics of CO2 reduction during the simultaneous attainment of the CO2‐HCO−3 equilibrium.
Metabolic Regulation of Steroidogenesis in Isolated Adrenal Cells of Rat
Authors: SHARMA Rameshwar K. , AHMED Nahed K. , SHANKER Gouri 
Published: March 2005

The data presented with the isolated adrenal cells, in the present study, show that adrenocorticotropin in the physiological concentration range stimulates the synthesis of guanosine 3′:5′‐monophosphate (cyclic GMP), protein kinase activity, and steroidogenesis in a concentration‐dependent manner without detectable rise in the levels of adenosine 3′:5′‐monophosphate (cyclic AMP). Millimolar concentrations of cyclic AMP and cyclic GMP, which stimulate corticosterone synthesis, also activate kinase activity and steroidogenesis in a sigmoid concentration‐response manner. The process of phosphorylation activated by corticotropin, cyclic AMP and cyclic GMP is not inhibited by eyeloheximide or actinomyin D. It is therefore proposed that the hormonal responses mediated by cyclic GMP and cyclic AMP are via the protein kinase enzymatic steps, and the inhibitory effect of' cycloheximide and actinomycin D in corticotropin‐stimulated steroidogenesis follows this step. In conjunction with our previous observations that the biosynthetic steps from (20S)‐20‐hydroxycholesterol to corticosterone are neither inhibited by cycloheximide nor affected by cyclic GMP, it is inferred that the rate‐limiting step of adrenal steroidogenesis is the transformation of cholesterol to (20S)‐20‐hydroxycholesterol and this very step is regulated by cyclic GMP and cyclic AMP.Of further significance are the findings that micromolar concentrations of cyclic AMP and cyclic GMP, which do not stimulate steroidogenesis, effectively stimulate protein kinase activity in a concentration‐dependent manner. It is therefore concluded that all cyclic‐nucleotide‐dependent protein kinase activities of the cell are not necessarily related to steroidogenesis.
Quantitative Estimates of Cytoplasmic and Nuclear Oestrogen Receptors in Chick Oviduct
Authors: SUTHERLAND Robert L. , BAULIEU Etienne‐Emile 
Published: March 2005

[3H]Oestradiol exchange techniques were developed for the determination of specific cestrogen receptor site concentrations in the cytoplasm and nuclei of chick oviduct cells. Non‐labelled receptor‐bound oestrogens were exchanged with [3H]oestradiol during a 24‐h incubation at 20 °C. 2 h at 30 °C or 45 min at 37 °C. Both ‘soluble’ and ‘insoluble’ nuclear receptors were stable for at least 6 h at 30 °C and 37 °C but a proportion (approx. 30%) of cytoplasmic sites from withdrawn chickens were inactivated after 2 h at 20 °C.The magnum of 4‐week‐old immature chickens (weight = 15 mg) contained 0.20 pmol of oestrogen receptor which corresponds to 4275 receptor sites/cell, when it is assumed that all magnum cells have equal concentrations of receptor. In primarily stimulated chickens of similar age which had received 10 × 1 mg of oestradiol benzoate/day, the magnum weighed approximately 800 mg and contained 8.65 pmol of oestrogen receptor (4610 sites/cell). Withdrawal from primary oestrogenic stimulation for 3–6 weeks resulted in a 110 mg magnum which contained 1.20 pmol of receptor (2225 sites/cell). Oviducts from immature and withdrawn chickens had the majority (73–77%) of their oestrogen receptor sites in the cytoplasmic fraction, while in primary stimulated chicken oviducts the majority (82%) of receptor sites were located in the nucleus.A single secondary injection of oestradiol, to oestrogen‐withdrawn chickens, resulted in apparent translocation of cytoplasmic receptors to the nucleus during the first hour after injection. The magnitude of the decline in cytoplasmic receptor, and the concurrent increase in nuclear receptor concentration, was dose‐dependent between 2 and 100 μg oestradiol‐ kg body weight. Larger doses of oestradiol up to 1 mg/kg did not increase the concentration of nuclear receptor above the maximum level seen at 100 μg oestradiol/kg. The initial rapid accumulation of nuclear receptor sites was followed by a period of progressive decline. By 15 h after an injection of 100 μg oestradiol kg, the concentration of nuclear sites had reached pre‐injection levels. During the same time period, the depleted cytoplasmic receptor levels were replenished such that they reached control values by 12 h and were about 150% of the pre‐injection level at 24 It.
Ca2+, K+‐Regulated Intramolecular Crosslinking of S‐100 Protein via Disulfide Bond Formation
Authors: CALISSANO Pietro , MERCANTI Delio , LEVI Andrea 
Published: March 2005

Reaction of the thiol reagent 5,5′‐dithio‐bis(2‐nitrobenzoic acid) (Nbs2) with the brain‐specific protein S‐100 favours stabilization of the quaternary structure of the protein via disulfide bond formation. This process is modulated by those cations (Ca2+ and K+) which are known to affect the conformation of the protein. Ca2+ markedly favours the reaction of S‐100 with Nbs2 but inhibits subsequent disulfide bond formation; K+, on the contrary, is much less effective in promoting interaction with Nbs2 but strongly stimulates disulfide bond formation. These findings are interpreted assuming that in presence of Ca2+ the three subunits forming the native S‐100 protein have two cysteine residues exposed to the solvent but mismatched to form disulfides while in presence of K+ the sulphydryl groups are in a less accessible position to Nbs2 but suitable for S‐S bond formation.Crosslinking of S‐100 subunits is characterized by the appearance in dodecylsulphate electrophoresis of two very close protein bands having a molecular weight almost identical to that of the native, undenatured protein but not of higher or lower‐molecular‐weight components. This finding, and the demonstration that both the crosslinked and native S‐100 proteins have identical profiles when analyzed by sucrose density centrifugation or gel chromatography indicate that disulfide bond formation occurs among subunits of the same molecule.
The Effect of Endogenous Phosphate on the H+/Mn2+ Ratio and the State of Mn2+ in the Mitochondrial Matrix
Authors: POZZAN Tullio , BRAGADIN Marcantonio , AZZONE Giovanni Felice 
Published: March 2005

Kinetics and stoichiometry of H+ extrusion and reuptake and of Mn2+ uptake and release have been measured in respiring liver mitochondria in the absence of external added Pi. H+ and Mn2+ fluxes are parallel during aerobic cation uptake but not during uncoupler induced cation release. The H+/Mn2+ is 1.24. Addition of SH reagents, in concentrations inhibiting the Pi carrier, modifies the kinetics of H+ extrusion and of Mn2+ uptake and release. The slow phase of uncoupler induced Mn2+ release is diminished. The H+/Mn2+ is increased to 1.72. Addition of SH reagents, after the phase of aerobic uptake is completed, results in a significant reduction of the extent of uncoupler‐induced Mn2+ release. The extent of reuptake of endogenous Pi during aerobic uptake of Mn2+ is about 8 nmol × mg protein−1.
Aerobic uptake of Mn2+ in the absence of external Pi results in an electron spin resonance spectrum which is the sum of two components. One, denoted as S, corresponds to Mn(H2O)62+. Another denoted as E, reflects spin exchange narrowing. In contrast to previous claims the following evidence suggests that the spin exchange component is due to Mn3(PO4)2 precipitate: (a) the dimension of the spin exchange spectrum is markedly reduced by abolition of Pi transport; (b) the spin exchange spectrum is released very slowly by addition of uncouplers under conditions where uncouplers cause a rapid deenergization of mitochondria, reuptake of H+ and release of cations; (c) the free matrix Mn2+ is released slowly after addition of uncoupler if there is a large spin exchange signal; however the free matrix Mn2+ is abolished rapidly by uncoupler when formation of the spin exchange signal is prevented by pretreatment with Ca2+; (d) the band width of the spin exchange fraction is independent of the Mn2+/protein ratio either under kinetic or steady state conditions; (e) the experimental spectrum recalls closely that obtained by computer simulation by assuming it as a combination of Mn(H2O)62+ and Mn3(PO4)2.
It is concluded that endogenous Pi affects the process of aerobic divalent cation uptake. A part of Mn2+ uptake in the absence of externally added anions, consists of a Mn3(PO4)2 precipitate. This accounts for a H+/Mn2+ ratio lower than 2.
Effect of Thyroid Hormones on Microsomal Fatty Acid Chain Elongation Synthesis in Rat Liver
Authors: LANDRISCINA Clemente , GNONI Gabriele V. , QUAGLIARIELLO Ernesto 
Published: March 2005

Evidence is presented that rat liver microsomal fatty acid chain elongation synthesis and desaturation, as well as acetyl‐CoA carboxylase and fatty acid synthetase, are strongly influenced by thyroid hormone level. Conversely, the fatty acid chain elongation system in mitochondria, unlike the oxidative capacity of palmitate, NADH, succinate and malate, does not seem significantly affected by the thyrotoxic state.In triiodothyronine‐induced or thyroxine‐induced hyperthyroidism, rat liver acetyl‐CoA carboxylase, fatty acid synthetase and microsomal chain elongation and desaturation reactions are not greatly affected after the first 10 days of treatment, while after longer intervals a respective increase in these activities is shown of up to 87, 116 and 65% after 22 days. In propylthiouracil‐induced hypothyroidism, all the above synthetic activities are strongly reduced immediately after three days of drug administration and diminished no further following longer periods.Although the pattern of synthesized fatty acids in the thyrotoxic state is similar to that obtained from normal subcellular rat fractions, the esterification process of fatty acids in microsomal lipids appears to be slightly inhibited in hypothyroid rats and increased following triiodothyronine or thyroxine administration. Finally, a reduction in the hepatic cyclic AMP level of about 41% is reported after 19 days of triiodothyronine‐administration to rats.On the basis of the observed insensitivity of the mitochondrial fatty acid chain elongation system to the thyrotoxic state, a tentative interpretation of its role in the hepatic cell is postulated.
Replenishment and Depletion of Citric Acid Cycle Intermediates in Skeletal Muscle.
Authors: SPYDEVOLD Øystein , DAVIS E. Jack , BREMER Jon 
Published: March 2005

The effects of various substrates on the concentrations of free amino acids, citric acid cycle intermediates and acylcarnitines were studied in perfused hindquarter of rat in presence of glucose and insulin in order to assess regulatory mechanisms of the level of citric acid cycle intermediates in skeletal muscle.

Acetate and acetoacetate effected a significant increase in the level of citrate cycle intermediates and accumulation of acetylcarnitine. These changes were accompanied by a reduction in the level of alanine. The concentration of AMP was significantly elevated.
Muscle mitochondria fixed 14CO2 in the presence of pyruvate. The products were identified as malate or citrate when whole and disintegrated mitochondria were used respectively. The fixation was greatly stimulated by acetylcarnitine.
Acetylcarnitine inhibited the production of pyruvate from malate by muscle mitochondria.
Perfusion with 2‐oxoisocaproate and 2‐oxoisovalerate promoted increases in the level of citric cycle intermediates, a drop in both alanine and glutamate, and accumulation of branched‐chain acylcarnitines. 2‐Oxoisocaproate also caused a reduction of alanine released from the muscle.
Perfusion with leucine and valine did not change the concentration of citric acid cycle intermediates, but elevated glutamate and still more the concentration of alanine.
It is concluded that citric cycle intermediate level in the perfused resting muscle is modified bya) conditions which change the concentration of acetyl‐CoA and thereby modify the rate of pyruvate carboxylation and decarboxylation of malate via malic enzymeb) conditions which change the concentration of pyruvate cause changes in alanine and cycle intermediates in the same direction via transmination reactionsc) conditions which change the concentrations of 2‐oxoacids which are converted to cycle intermediates via oxidation.
Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit
Authors: SHUSTER Robert C. , HOUDEBINE Louis‐Marie , GAYE Pierre 
Published: March 2005

The quantity of casein mRNA in the rabbit mammary gland was assayed during the course of pregnancy, by translation of casein mRNA in a reticulocyte lysate and by hybridization to DNA complementary to purified casein mRNA. Both methods indicated that the major increases in the concentration of casein mRNA in both polysomal and total cellular RNA occurred between the 18th and 25th day of pregnancy. The change in casein mRNA concentration during this period coincided with a sharp rise in casein synthesis in mammary gland explants suggesting that the levels of casein mRNA determine the rate of casein synthesis in the mammary gland.The sensitivity of the hybridization assay made it possible to detect the presence of casein mRNA in virgin animals and during the very early stages of pregnancy. At day 5, casein mRNA was found associated with polysomes indicating that there was probably some casein synthesis at this early stage of gestation. These results suggest that the hormones controlling lactogenesis in the rabbit may function by augmenting the rate of casein mRNA synthesis rather than initiating transcription of previously inactive genes.
Acetyl‐Coenzyme‐A Carboxylase of Candida lipolytica
Authors: MISHINA Masayoshi , KAMIRYO Tatsuyuki , NUMA Shosaku , TANAKA Atsuo , FUKUI Saburo 
Published: March 2005

Acetyl‐coenzyme‐A carboxylase has been isolated in homogeneous form from Candida lipolytica. The homogeneity of the enzyme preparation is evidenced by analytical ultracentrifugation, dodecylsulfate‐polyacrylamide gel electrophoresis and Ouchterlony double‐diffusion analysis. The purified enzyme exhibits a specific activity of 8.0 U/mg protein at 25°C and contains 1 mol biotin/263000 g protein. The sedimentation coefficient (S20, w) of the enzyme is 18 S. It has been shown by dodecyl‐sulfate‐polyacrylamide gel electrophoresis that the enzyme possesses only one kind of subunit with a molecular weight of 230000. This finding, together with the biotin content, indicates that the C. lipolytica enzyme has a highly integrated subunit structure.The C. lipolytica enzyme is very labile, but is stabilized by glycerol. The enzyme is markedly activated by poly(ethyleneglycol), the activation being due principally to a decrease in the Km values for substrates. Even in the presence of this activator, the Km value for acetyl‐CoA of the C. lipolytica enzyme is much higher than that of the enzyme from Saccharomyces cerevisiae and animal tissues. The C. lipolytica enzyme, unlike the enzyme from animal tissues, is not activated by citrate.
Nucleolar DNA‐Dependent RNA Polymerase from Rat Liver
Authors: MATSUI Takashi , ONISHI Toshio , MURAMATSU Masami 
Published: March 2005

DNA‐dependent RNA polymerase I (or A) was purified from rat liver nucleoli. DNA was effectively removed from the solubilized enzyme with a defined concentration of polyethyleneglycol. The enzyme was purified further with successive DEAE‐Sephadex and phosphocellulose column chromatography followed by glycerol gradient centrifugation. The procedure yielded an electro‐phoretically homogeneous enzyme with a specific activity 400 times that of the nucleolar extracts. The recovery of the activity was approximately 20%.The RNA polymerase I eluted as a single peak from DEAE‐Sephadex was separated into two distinct peaks by a phosphocellulose column. The first peak eluting at about 0.12 M ammonium sulfate was designated as RNA polymerase IA and the second peak eluting at about 0.18 M as RNA polymerase IB. In normal rat liver nucleoli IA enzyme comprised approximately 20% of the total RNA polymerase I activity and the IB enzyme comprised approximately 80%.On sodium dodecyl sulfate polyacrylamide gel electrophoresis, enzyme IB contained five subunits with molecular weights of 195000 (a), 130 000 (b), 65 000 (c), 40 000 (d), and 19 000 (e) at nearly equimolar amounts. The calculated molecular weight of the enzyme (449000) agreed well with that predicted from the sedimentation coefficient of the enzyme. Enzyme IA contained identical subunits except that subunit c was absent. Preliminary studies could not demonstrate any significant differences in template specificity between IA and IB enzyme.