bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proteolytic enzymes in sea urchin eggs: Characterization, localization and activity before and after fertilization
Authors: Krischer Kenneth N. , Chambers Edward L. 
Published: February 2005

AbstractThe pH versus proteinase activity curve (casein or hemoglobin plus urea substrate) for homogenates of unfertilized Lytechinus eggs reveals two regions of maximum activity: one between pH 3.5 and 4.3, and another of far greater magnitude from pH 8.0 to 11.0. The two classes of proteinases can be separated on a sucrose density gradient. Both the acid and alkaline proteinases in homogenates prepared in isotonic monovalent salt solutions are remarkably stable at pH 7.4 and 0°C. Using synthetic peptide substrates, an enzyme with the specific esterase activity of chymotrypsin was demonstrated; this enzyme accounts for the major part of the proteinase activity at alkaline pH. In addition, an enzyme with specific esterase activity of trypsin was shown to be present, but of low activity. The proteinase activity at acid pH is largely due to an enzyme resembling cathepsin D. The data also suggest the presence of cathepsin B and cathepsin IV (or catheptic carboxypeptidase).When eggs are homogenized in isotonic NaCl plus KCl at pH 7.4, 0.02 M tris buffer at 0°C, all of the alkaline proteinase, and 85–90% of the acid proteinase activity is sedimented at 10,000 g. The presence of any proteinase activity in the supernatant phase represents an artifact of the preparative procedures used. The granules which possess the proteinase activity are contained entirely in the yolk fractions; and the acid proteinase is contained in a population of granules which sediment more readily than those which contain the alkaline proteinase. The acid proteinase resembles the lysosomal acid hydrolases in that it is readily released from the particulates; in contrast, the alkaline proteinase is bound relatively firmly.In contradistinction to reports in the literature, no changes in proteinase activity nor intracellular distribution could be detected following fertilization.
Comparative aspects of poliovirus replication
Authors: Levintow Leon , Michael Bishop J. 
Published: February 2005

AbstractTo the extent that parallel experiments with picornaviruses and RNA bacteriophages can be compared, the results suggest that their mechanisms of RNA replication are basically similar, despite fundamental differences between the two groups of viruses with respect to the control of the expression of genetic information.The significance of the extracted multi‐stranded replicative forms of viral RNA is discussed and it is concluded that, if not identical to the corresponding, intracellular forms, the extracted structures are meaningful derivatives of specific native forms.
Differential temperature sensitivity of normal and cancer cells in culture
Authors: Levine Elliot M. , Robbins Elliott B. 
Published: February 2005

AbstractSerially‐propagated growing heteroploid and growing diploid cell cultures do not survive incubation at 42° for 24 hours, whereas contact‐inhibited diploid monolayers are still viable after at least nine days at this elevated temperature. Heat‐treated heteroploid HeLa cells and growing diploid cells exhibit a variety of morphologic abnormalities, but contact‐inhibited cells are only minimally affected. A similar differential temperature sensitivity exists in the synthesis of cellular macromolecular components such as DNA, RNA, and protein: incorporation of radioactive precursors is drastically reduced in growing diploid and heteroploid cells after 24 hours at 42°, but not in contact‐inhibited cells. Incorporation of labelled glucose, choline, or linolenic acid is actually enhanced in heat‐treated contact‐inhibited cells.
Modification of rabbit muscle aldolase in Vivo and in Vitro
Authors: Lai C. Y. , Horecker B. L. 
Published: February 2005

AbstractRabbit muscle aldolase in situ appears to undergo several modification reactions. One of these, specific deamidation of an asparagine residue near the COOH‐terminus, appears to account for the presence of two types of subunits in the enzyme isolated from the muscle of adult rabbits. Evidence for a second modification is the presence of approximately one equivalent of organic phosphorus in the crystalline enzyme preparations. The presence of this phosphate group may be related to the incomplete release of COOH‐terminal tyrosine residues from the enzyme protein with carboxypeptidase. Two reactions with substrate, both leading to the incorporation of organic phosphorus, have been demonstrated in vitro. A reaction with glyceraldehyde 3‐phosphate or erythrose 4‐phosphate leads to loss of catalytic activity and change in the susceptibility of COOH‐terminus to carboxypeptidase. The other reaction, with fructose 1,6‐diphosphate at low concentration, does not affect the activity of the enzyme, nor its susceptibility towards the action of carboxypeptidase. Either or both of these may be related to the changes which appear to occur during the life of the enzyme in vivo.
Biosynthesis of the α chains of collagen
Authors: Piez Karl A. 
Published: February 2005

AbstractThe α chains of collagen are synthesized like other proteins by the sequential addition of amino acids beginning at the amino‐terminal end and continuing for over 1000 amino acids. In addition to amino acid assembly, hydroxylation of certain prolyl and lysyl residues is required to complete the molecule. Approximately 4.8 minutes is necessary for the entire process. After extrusion from the cell, specific lysyl residues are oxidatively deaminated to the aldehyde allysine. An analogous conversion probably occurs with hydroxylysine. Cross‐linking results from the condensation of an aldehyde on one chain with an aldehyde or an ϵ‐amino group on another chain.
Control of macromolecular synthesis in proliferating and resting syrian hamster cells in monolayer culture. I. Ribosome function
Authors: Stanners C. P. , Becker H. 
Published: February 2005

AbstractThe rate of protein synthesis per cell in cultured hamster embryo fibroblasts in the stationary growth phase falls to about one third of the rate in the exponential growth phase. This reduction can be entirely accounted for by the following observations: (1) the average cell in stationary phase contains about one‐half the number of ribosomes per cell compared to the average cell in exponential phase; (2) only two thirds of the ribosomes are bound to polysomes in stationary phase, while nearly all of the ribosomes are polysome‐bound in exponential phase.In stationary phase, ribosomes which are polysome‐bound function with the same efficiency and produce proteins of approximately the same average length as in exponential phase. Experimental findings are presented which suggest that the generation of a higher proportion of free ribosomes in stationary phase in not due to a limitation in messenger RNA, but to a decreased attachment probability of ribosomes to messenger RNA.
Control of macromolecular synthesis in proliferating and resting syrian hamster cells in monolayer culture. II. Ribosome complement in resting and early G1 Cells
Authors: Becker H. , Stanners C. P. , Kudlow J. E. 
Published: February 2005

AbstractUsing a new, sensitive and quantitative technique for determining the ribosomal‐RNA content of a measured number of cells, the cellular ribosome complement was compared for cultured hamster embryo cells in the stationary growth phase and in the early G1 phase of the cell cycle. Cells from stationary phase cultures were found to contain less than 70% of the ribosome complement of the early G1 phase cells, though the volumes of the two cell types were similar. This would imply that the stationary phase cell is physiologically different from a cell merely arrested at some point in the cell cycle.
Characterization of the factor in L‐cell conditioned medium capable of stimulating colony formation by mouse marrow cells in culture
Authors: Austin P. E. , McCulloch E. A. , Till J. E. 
Published: February 2005

AbstractMedium harvested from cultures of mouse L‐cells contains “conditioning factor activity” (CFA) that may be detected by its ability to stimulate colony formation by mouse marrow cells in culture. The active material has been characterized and appears to be a glycoprotein with properties similar to those reported for the colony‐stimulating activity in human urine. Characterization of trypsin‐digested material indicated that only part of the molecule is essential for biological activity.The CFA has been partially purified from serum‐free L‐cell conditioned medium, and evidence has been obtained that radioactivity derived from labelled valine or glucosamine may be incorporated into the factor. L‐cell conditioned medium appears to be a convenient source of partially‐purified, highly active material, suitable for use in studies on its mechanism of action.
Cyclic AMP and calcium exchange in a cellular slime mold
Authors: Chi Yea‐Yuan , Francis David 
Published: February 2005

AbstractCyclic AMP is known to be an effective chemotactic agent for amebae of the cellular slime mold D. discoideum. A large amount of information from experiments on metazoa suggested that one cellular effect of cyclic AMP might be to alter the permeability of the cell membrane to Calcium or Sodium ions.On the basis of this information experiments were designed to test the effect of cyclic AMP on outflow of labeled Calcium or Sodium ions from amebae of D. discoideum. It was found that addition of cyclic AMP at 10−4M resulted in a large increase of Ca45 outflow from cells at the pre‐aggregative or aggregative stage of development. No effect was found on Na22 outflow.It is suggested that this effect on Calcium permeability of the membrane is related to the chemotactic influence of ATP by some action on the contractile mechanism for ameboid movement. The phenomenon may be distinct from the enzyme inductive activity of cyclic AMP known for bacteria, and perhaps occurring in the cellular slime molds as well.
Gene expression in synchronized lymphocytes: Studies on the control of synthesis of immunoglobulin polypeptides
Authors: Lerner R. A. , Hodge L. D. 
Published: February 2005

AbstractA concept has been suggested that the role of immunogen is to stimulate resting cells to enter a phase of the cell cycle in which the synthesis of immunoglobulin is obligatory. This process conceivably involves the initial union of cells with immunogen followed by a subsequent transition from resting to proliferating cell. Several aspects of an in vitro cellular transition have been investigated using cultured WIL2 lymphocytes which are shown to enter the G1 phase of the cell cycle upon release from rest. This transition is associated with phenotypic changes in the cells manifested by differences in density of individual cells and the amount and profile of polyribosomes. An increase in the rate of synthesis of total protein and specific immunoglobulin polypeptides accompanies the G0 to G1 transition. Agents useful in bacterial and other mammalian cell systems to probe translational versus transcriptional control mechanisms are active in these lymphocytes. This cellular model appears to offer unique opportunities to approach regulatory problems in cell biology because large numbers of synchronized cells are obtainable in which specific messenger‐RNAs and their corresponding polypeptides can be isolated in relatively pure form.
Studies on the regulation of granulopoiesis. V. Effect of marrow cells on colony stimulating activity in serum
Authors: Morley Alec , Rickard Kevin A. , Quesenberry Peter , Garrity Marianne , Stohlman Frederick 
Published: February 2005

AbstractSerum obtained from irradiated mice lost its colony stimulating activity when incubated with normal marrow cells. The loss of activity appeared to be due to absorption or inactivation of the active factor in the serum rather than to production of an inhibitor by the cells.
Energy transfer in a bioluminescent system
Authors: Morin James G. , Hastings J. W. 
Published: February 2005

AbstractMany (but not all) of the bioluminescent systems in coelenter‐ates involve energy transfer from an excited product molecule of the calcium activated photoprotein to a second species, the green fluorescent protein, with emission at 508 nm from its excited state. Although all the luminescent coelen‐terates studied possess photoproteins, not all of them have the green fluorescent protein. This green fluorescent molecule is localized in the luminescent cells; they can thus be easily distinguished by fluorescence microscopy. The active components occur in subcellular particles; these have been isolated in an active form by homogenization in isotonic (to sea water) salt solutions.
Viral‐induced fusion of human cells. II. Heterokaryocytes between human cells from different donors, and between human cells and those from other species: Formation and properties
Authors: Velázquez Antonio 
Published: February 2005

AbstractA simple method is described for effecting the formation of heterokaryocytes between different lines of human diploid fibroblasts, and between human diploid fibroblasts and cultured cells derived from other species. In the case of mixed monolayer cultures of human diploid fibroblasts exposed to UV‐inactivated Sendai virus, the proportion of nuclei in heterokaryocytes is between 25 and 35%. The heterokaryocytes engage in de novo protein synthesis. No evidence of hybrid enzymes was found in mixed cultures of human and mouse cells which had been exposed to Sendai virus and which therefore presumably contained mouse‐human heterokaryocytes. However, with the available data, it is not possible to distinguish between the absence of synthesis of hybrid enzymes and the synthesis of hybrid enzymes in amounts insufficient to permit their detection.
Enzyme kinetics in mammalian cells. III. Regulation of activities of galactokinase, galactose‐1‐phosphate uridyl transferase and uridine diphosphogalactose‐4‐epimerase in human erythrocytes
Authors: Hill Helene Z. 
Published: February 2005

AbstractThe sequential enzyme assay as previously described has been used to study various effects on the three enzymes in human red cells involved in the phosphorylation of galactose: galactokinase, galactose‐1‐phosphate uridyl transferase and uridine diphospho‐galactose‐4‐epimerase.
Enzyme activities in undiluted lysates appear to reflect the respective activities in whole cells.
Added extracellular Gal‐1‐P, G‐1‐P, UDPGal and UPDG do not affect enzyme activities in whole cells.
The kinase and transferase enzymes do not appear to be associated with the membrane fraction of the red cells.
Galactokinase activity is inhibited by G‐6‐P and Gal‐1‐P, but not by glucose, G‐1‐P, UDPG, UDPGal, UTP or NAD+. It is inhibited by ATP and ADP in high concentration.
Galactose‐1‐phosphate uridyl transferase activity is inhibited by G‐1‐P, G‐6‐P, UDPG, UDPGal, ATP, and ADP. It is not affected by UTP, NAD+, or galactose.
Uridine diphospho‐galactose‐4‐epimerase activity is inhibited by UDPG, ATP, ADP, UTP and NADH. It is stimulated by NAD+ and possibly by Gal‐1‐P. It is unaffected by G‐1‐P, G‐6‐P.
The rates of the three reactions decrease with decreasing temperature. The activities of transferase and epimerase are inactivated at the same rate, the kinase activity is inactivated more slowly.
Dilution experiments indicate the presence in lysates of a pool of UDPG (or, possibly UDPGal) which regulates the activities transferase and the epimerase enzymes.
Results of dilution experiments suggest that the radioactive product of the transferase enzyme is different from commercially available UDPGal‐u‐14C.
ATP, UTP and UDPG interact with some substance(s) in the red cell lysate to cause a time dependent inactivation of the epimerase. These interactions are the result of glucose metabolism.
Development of chick embryo liver during organ culture: Requirement for zinc‐insulin
Authors: Benzo Camillo A. , de la Haba Gabriel 
Published: February 2005

AbstractLivers from five‐day chick embryos maintained as organ cultures on Eagle's minimum essential medium (MEM) develop an ultrastructure similar to more mature liver cells, except for glycogen deposits and the smooth endoplasmic reticulum (SER) normally associated with such deposits. The enzymes, glycogen synthetase and glycogen phosphorylase, failed to develop in these cells. The addition of zinc‐free insulin (insulin‐HCl) to MEM promoted the development of small amounts of SER in the cultured cells, as well as an increase in both glycogen synthetase and phosphorylase activities. The addition of zinc‐insulin also stimulated an increase in the activities of both enzymes, and promoted the development of greater amounts of SER and the deposition of glycogen, as well. In addition, both forms of insulin not only prevented the fall of total tissue protein which occurs during organ culture on MEM, but also stimulated net protein synthesis in the explanted liver (Benzo and de la Haba, '71).
Isolation of inclusion bodies from rabbit lung parenchyma
Authors: Hoffman Lee 
Published: February 2005

AbstractThe mitochondrial‐plus‐lysosomal fraction of rabbit lung parenchyma was studied by equilibrium density centrifugation in continuous sucrose density gradients (specific gravity 1.035 to 1.250). High concentrations of lysosomal marker enzymes were found both in a broad band at density 1.15–1.18, a density typical for lysosomes, and in a band at density 1.06–1.07. This light density band also had the highest specific activity of phospholipid, which thin layer and gas‐liquid chromatography showed to be primarily lecithin with a high content of palmitic acid residues. Electron microscopy of material from the light density band showed a homogeneous array of particles which bear a strong resemblance to the inclusion bodies of the type II alveolar epithelial cell as seen in electron micrographs of rabbit lung tissue sections. These data suggest that the light density band is an isolation of intact type II alveolar epithelial cell inclusion bodies, which previous studies have implicated as the storage site of the phospholipid moiety of pulmonary surfactant.
Correlative secretion of protein, lactose and K+ in milk of the goat
Authors: Silcock W. Ross , Patton Stuart 
Published: February 2005

AbstractRates of secretion of milk constituents (fat, protein, lactose, Na+ and K+) in the lactating goat were measured under normal circumstances and after injections of ouabain. In all experiments a close association was noted in the secretion rates for protein, lactose and K+. Under the influence of ouabain, the concentration of Na+ in the milk tended to rise and that of K+ to fall. The rate of milk fat secretion varied independently from the rates for the other constituents. It is reasonably assumed that the principal mechanism of milk protein secretion is by emptying of Golgi vesicles through the plasma membrane. The close correlation in rates for protein, lactose and K+ supports the contention that all three are assembled in Golgi vesicles and secreted by the same mechanism.
Mechanisms of acquired resistance to acute heat shock in cultured mammalian cells
Authors: Reeves O. Raymond 
Published: February 2005

AbstractA clonal strain of mammalian cells with increased resistance to acute heat shock at 46° was compared with the heat‐sensitive parental line from which it was derived for possible differences that might account for this acquired resistance. Studies on synchronized populations of the two cell strains did not reveal any differential heat sensitivities in the various parts of the cell cycle (G1, S, G2) within either the sensitive or resistant populations. During thermal stress both cell types exhibited marked inhibition of ability to incorporate isotopically labeled precursors into macromolecular RNA, DNA, and protein.However, significant differences were observed between the sensitive and resistant cells in the amount of leakage of materials from the two cell types during heat stress and in their relative rates of recovery after stress. Sensitive cells pre‐labeled with 3H‐uridine released considerably more acid‐soluble (cold, 5% TCA) label‐containing materials during heat stress than did pre‐labeled resistant cells. This differential release of uridine‐containing materials was not paralleled by a generalized differential leakiness to other compounds. In addition, the resistant cells were found to regain the capacity to synthesize vital macromolecules sooner, and at initially faster rates, than the sensitive cells after stress.These results suggest that permeability changes causing decreased leakage of uridine‐containing materials during heat stress combined with accelerated rates of recovery of synthesis of essential macromolecules after stress may be important cellular mechanisms in resistance to heat shock.
The carbohydrate content of control and virus‐transformed cells
Authors: Hartmann J. F. , Buck C. A. , Defendi V. , Glick M. C. , Warren L. 
Published: February 2005

AbstractThe levels of carbohydrates were measured in cells before and after transformation with DNA and RNA‐containing oncogenic virus. The most consistent finding was a markedly lower content of L‐fucose in all transformed cells relative to their normal counterpart. The cell pellet from a line of Chinese hamster cells transformed with polyoma or SV‐40 viruses showed a marked decrease in the level of carbohydrates. However, when the carbohydrate levels were calculated for the whole system (cells plus wash) the transformed cells except for L‐fucose had almost the same amount of carbohydrate as the controls. The levels of various carbohydrates in cells transformed by Rous sarcoma virus were the same or were elevated above the controls. Here consideration of the washes did not alter the results. Possible explanations for the results and causes of error in these comparative studies are discussed.
Ontogeny of the human lymphoid system: Study of the cytological maturation and the incorporation of tritiated thymidine and uridine in the foetal thymus and lymph node and in the infantile thymus
Authors: Papiernik Martine 
Published: February 2005

AbstractThe study of the cytological evolution of the foetal thymus enables us to distinguish an early foetal period (up to 20 weeks) from a late foetal period. The cytological maturation is achieved at 20 weeks of gestation. The thymus in the late foetal phase is comparable to that of the child.The study of the lymphopoietic function shows a higher activity in the foetal thymus up to 20–22 weeks, lymphopoiesis is also slightly increased, in the thymus of the child up to the age of three years. The study of the contribution of the various cell types to the cellularity of the thymus, emphasizes the importance of the medium lymphocytes in the early foetal period. The small lymphocytes though to a lesser extent, are also capable of division in the foetal thymus and in the infantile thymus. Incorporation of uridine is also increased in the early foetal thymus.Cytological composition and lymphopoiesis of the foetal thymus and lymph node, have been compared.
Sedimentation of single human red blood cells. Differences between normal and glutaraldehyde fixed cells
Authors: Jay Alfred W. L. , Canham Peter B. 
Published: February 2005

AbstractThe sedimentation behaviour of single human red blood cells fixed with glutaraldehyde at pH 7.4 and 6.4 was studied and compared to resiflts previously reported for normal fresh cells. The cells fixed at pH 7.4 were observed to have normal shapes while those fixed at pH 6.4 were more spherical and less disc‐like. Fixation of glutaraldehyde removed “membrane flicker,” resulting in increased stability as indicated by a decrease in the number of orientation changes per minute from 2.93 ± 0.16 (SEM) to 1.74 ± 0.10 (SEM). An orientation change was defined as a change of 45° in any direction. Fixation also increased the edge‐to‐flat time preference ratio from 2.5 to 4.7, and increased the sedimentation velocities in all three orientations, despite a measured 2.5% decrease in mean cell density.Fixation of cells at pH 6.4 showed that the decrease in stability and preference for the on‐edge orientation was associated with an increase in the sphericity of the cell.