bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of fluxes at low concentrations of l-tri-iodothyronine with rat liver cells and their plasma-membrane vesicles. Evidence for the accumulation of the hormone against a gradient
Authors: Rao Govind S. , Rao Marie Luise , Thilmann Astrid , Quednau Hans D.
Published: August 2015

1. Influx and efflux of l-tri-[125I]iodothyronine with isolated rat liver parenchymal cells and their plasma-membrane vesicles were studied by a rapid centrifugation technique. 2. At 23°C and in the concentration range that included the concentration of free l-tri-iodothyronine in rat plasma (3–5pm) influx into cells was saturable; an apparent Kt value of 8.6±1.6pm was obtained. 3. At 5pm-l-tri-[125I]iodothyronine in the external medium the ratios of the concentrations inside to outside in cells and plasma-membrane vesicles were 38:1 and 366:1 respectively after 7s of incubation. At equilibrium (60s at 23°C) uptake of l-tri-[125I]iodothyronine by cells was linear with the hormone concentration, whereas that by plasma-membrane vesicles exhibited an apparent saturation with a Kd value of 6.1±1.3pm. 4. Efflux of l-tri-[125I]iodothyronine from cells equilibrated with the hormone (5–123pm) was constant up to 21 s; the amount that flowed out was 17.7±3.8% when cells were equilibrated with 5pm-hormone. When plasma-membrane vesicles were equilibrated with l-tri-[125I]iodothyronine (556–1226pm) 66.8±5.8% flowed out after 21 s. 5. From a consideration of the data on efflux from cells and binding of l-tri-[125I]iodothyronine to the liver homogenate, as studied by the charcoal-adsorption and equilibrium-dialysis methods, it appears that 18–22% of the hormone exists in the free form in the cell. 6. Vinblastine and colchicine diminished the uptake of l-tri-[125I]iodothyronine by cells but not by plasma-membrane vesicles; binding to the cytosol fraction was not affected. Phenylbutazone, 6-n-propyl-2-thiouracil, methimazole and corticosterone diminished the uptake by cells, plasma-membrane vesicles and binding to the cytosol fraction to different extents. 7. These results suggest that at low concentrations of l-tri-[125I]iodothyronine rat liver cells and their plasma-membrane vesicles accumulated the hormone against an apparent gradient by a membrane-mediated process. Contribution of cytoplasmic proteins to uptake by plasma-membrane vesicles was negligible. The amount of l-tri-[125I]iodothyronine required to achieve half-maximal uptake agrees with that occurring in the free form in the blood, conferring physiological importance to the transporting system in the plasma membrane of the liver cell.
Adsorptive pinocytosis of 125I-labelled lactate dehydrogenase isoenzymes H4 and M4 by rat yolk sacs incubated in vitro
Authors: Kooistra T , Williams K E
Published: August 2015

The pinocytic uptake of 125I-labelled porcine lactate dehydrogenase isoenzymes H4 and M4 by 17.5-day rat visceral yolk sac incubated in vitro was saturable and binding obeyed Michaelis-Menten kinetics. The uptake characteristics of the two isoenzymes were very similar. For the H4 and the M4 isoenzymes, the dissociation constants of the protein-plasma-membrane complex were 0.62 microM and 0.84 microM respectively, and the maximum rates of uptake 0.13 and 0.26 nmol/mg of yolk-sac protein per h respectively. These findings contrast with those from studies in vivo, which show the M4 form is taken up by rat liver sinusoidal cells at a much higher rate than the H4 form, and point to different recognition systems for the adsorptive pinocytosis of simple non-conjugate proteins in yolk-sac epithelial cells and liver sinusoidal cells. Competition experiments indicate that binding of the H4 isoenzyme to the yolk-sac cells is restricted to hydrophobic interactions, whereas the binding of the M4 isoenzyme involves hydrophobic as well as positively charged sites on the protein molecules.
Activation of adenylate cyclase in bovine corpus-luteum membranes by human choriogonadotropin, guanine nucleotides and NaF
Authors: Lydon Nicholas B. , Young John L. , Stansfield David A.
Published: August 2015

1. Preincubation of luteal membranes with human choriogonadotropin results in the formation of an activated state of adenylate cyclase which is not reversed by washing and which is limited only by the absence of guanine nucleotides, whereas preincubation with GTP yields only a partially activated adenylate cyclase which requires the presence of both GTP and human choriogonadotropin during assay to demonstrate maximal activity. 2. Preincubation of luteal membranes with GTP and human choriogonadotropin does not lead to a synergistic increase in wash-resistant activity. 3. Luteal membranes that had been preincubated with GTP and hormone exhibited a decreasing rate of cyclic AMP synthesis during the adenylate cyclase assay incubation; addition of GTP during the assay incubation reversed the decrease. 4. Membranes that had been preincubated in the absence of guanine nucleotide and hormone showed a ‘burst’ phase of cyclic AMP synthesis when GTP was present in the assay incubation and a ‘lag’ phase with p[NH]ppG (guanosine 5′-[β,γ-imido]triphosphate) present in the assay. The presence of human choriogonadotropin with either nucleotide in the assay incubation eliminated the curvatures in plots observed with guanine nucleotides alone. 5. Luteal adenylate cyclase was persistently activated by preincubation with p[NH]ppG alone or in combination with human choriogonadotropin; the activation caused by p[NH]ppG alone was still increasing after 70min of preincubation, whereas that caused by p[NH]ppG in the presence of hormone was essentially complete within 10min of preincubation. 6. Luteal adenylate cyclase that had been partially preactivated by preincubation with p[NH]ppG was slightly increased in activity by the inclusion of further p[NH]ppG in the adenylate cyclase assay incubation, but more so with p[NH]ppG and hormone. Human choriogonadotropin alone caused no further increase in the activity of the partially stimulated preparation unless p[NH]ppG was also added to the assay incubation. 7. GTP decreased the activity of adenylate cyclase in membranes that had been partially preactivated in the presence of p[NH]ppG; the decrease in activity was greater when GTP and hormone were present simultaneously in the assay. 8. The results indicate that stable activation states of adenylate cyclase can be induced by preincubation of luteal membranes in vitro with human choriogonadotropin or p[NH]ppG, and that in the presence of p[NH]ppG the hormone may accelerate events subsequent to guanine nucleotide binding. Stable activation of luteal adenylate cyclase by prior exposure to GTP is not achieved. The involvement of GTPase activity and of hormone-promoted guanine nucleotide exchange in the modulation of luteal adenylate cyclase activity is discussed.
Heterogeneity of the molecular defect in human dihydropteridine reductase deficiency
Authors: Firgaira F A , Choo K H , Cotton R G H , Danks D M
Published: August 2015

Radioimmunoassay, immunoprecipitation, affinity chromatography and two-dimensional gel electrophoresis were used to test cultured cells from three families with dihydropteridine reductase deficiency for a catalytically incompetent product of the mutant gene. No mutant enzyme was detected in one dihydropteridine reductase-deficient homozygote or in her parents. A second homozygote and both her parents had easily detectable concentrations of inactive mutant enzyme. In a third family one parent fitted into each of these categories.
Chemical and physical characterization of a proline-rich polypeptide from sheep colostrum
Authors: Janusz M , Starościk K , Zimecki M , Wieczorek Z , Lisowski J
Published: August 2015

A proline-rich polypeptide isolated from sheep colostrum is described. The molecular weight of the polypeptide determined by gel filtration is 17 200. However, in the presence of guanidinium chloride the molecular weight found is about 6000. The polypeptide contains about 22% of proline, a high proportion of non-polar amino acids, a low percentage of glycine, and no alanine, arginine and cysteine residues. The only N-terminal amino acid found is leucine. C.d. spectra in water and in 50% (v/v) trifluoroethanol suggest the presence of block sequences of proline residues forming helices of polyproline II type. The proline-rich polypeptide is soluble at 4 degrees C but is reversibly precipitated on warming to room temperature. Maximal precipitation is observed at pH 4.6 and at ionic strength above 0.6. The precipitation depends on the concentration of the polypeptide. No effect of other proteins, Ca2+ and Zn2+ ions on the precipitation of the polypeptide was found. The proline-rich polypeptide is not an amphipathic protein. The lack of effect of the polypeptide on proteolytic enzymes ruled out the possibility that it is an inhibitor of proteinases.
Isoelectric-focusing patterns of cyclic nucleotide phosphodiesterase from rat heart
Authors: Némoz G , Prigent A F , Pageaux J F , Pacheco H
Published: August 2015

1. Isoelectric focusing on a flat gel bed of the rat heart cytosolic fraction resolved cyclic nucleotide phosphodiesterase activity into several forms, characterized by their substrate specificity, kinetic constants and dependence towards Ca2+ and calmodulin. A peak of pI 4.9 displayed 20 times more affinity for cyclic GMP than for cyclic AMP and was markedly inhibited by EGTA. A less substrate-specific form, only slightly sensitive to EGTA inhibition, focused at pH 5.45. Several overlapping peaks detected between pH 5.55 and pH6 specifically hydrolysed cyclic AMP, with non-Michaelian kinetics; these peaks were insensitive to Ca2+ chelation. 2. Isoelectric focusing did not dissociate enzyme-calmodulin complexes, as none of the resulting peaks was activatable by calmodulin plus Ca2+. 3. Some new information on rat cardiac phosphodiesterase is obtained with this technique, which is convenient for routine analytical studies of phosphodiesterase, as well as for preparative purposes.
Kinetics of plasmin inhibition in the presence of a synthetic tripeptide substrate. The reaction with pancreatic trypsin inhibitor and two forms of α 2-plasmin inhibitor
Authors: Petersen L C , Clemmensen I
Published: August 2015

The progressive inhibition of plasmin by pancreatic trypsin inhibitor and by alpha 2-plasmin inhibitor in the presence of D-valyl-L-leucyl-L-lysine 4-nitroanilide was investigated. The kinetics with plasmin were compared with those with miniplasmin. The kinetic properties of two functionally different forms of alpha 2-plasmin inhibitor described by Clemmensen [(1979) in The Physiological Inhibitors of Coagulation and Fibrinolysis (Collen. D., Wiman, B & Verstraete, M., eds.), pp 131-136, Elsevier, Amsterdam] were characterized. The two forms differ in their plasminogen-binding capability, and this difference can account for a difference in secondary site interaction suggested from the kinetics. The binding of inhibitor to miniplasmin is a simple pseudo-first-order reaction with both pancreatic trypsin inhibitor and the two alpha 2-plasmin inhibitor forms. Such simple kinetics are also observed for the reaction between plasmin and the non-plasminogen-binding form of alpha 2-plasmin inhibitor. More complicated kinetics are obtained for the reaction between plasmin and the alpha 2-plasmin inhibitor form that binds to plasminogen. With both forms of the alpha 2-plasmin inhibitor, a complex stable to acetic acid/urea and gel electrophoresis is present and fully developed 15 s after initiation of the reaction with plasmin.
Estimation of deuteration levels in whole cells and cellular proteins by 1H n.m.r. spectroscopy and neutron scattering
Authors: Perkins S J
Published: August 2015

Methods using conventional Fourier transform 1H n.m.r. spectroscopy at 250 MHz for the determination of the overall deuteration levels of cells cultured in media containing 2H2O or deuterated carbon sources are described. These were developed for Escherichia coli as a model, and extended to Neurospora crassa hyphae and mouse myeloma cells P815. The results were investigated by 1H n.m.r. and neutron scattering measurements on deuterated proteins that were obtained from E. coli. It is concluded that 1H n.m.r. is able to observe the soluble proteins of E. coli in certain cases, that deuteration levels can be determined by 1H n.m.r. for small quantities of proteins in their native state, and that glycerol is a more efficient carbon source than glucose for the deuteration of E. coli proteins.
A rapid purification of bovine testicular hyaluronidase by chromatography on dermatan sulphate-substituted 1,6-diaminohexane–sepharose 4B
Authors: Lyon M , Phelps C F
Published: August 2015

The binding of bovine testicular hyaluronidase to AH-Sepharose (1,6-diaminohexane--Sepharose) gels substituted with (1) dermatan sulphate, (2) desulphated dermatan sulphate, (3) heparin and (4) de-N/O-sulphated, re-N-acetylated heparin was investigated. Hyaluronidase was found to bind to (1) and (3), but not (2) and (4). On the basis of these observations a preparative scheme for the purification of testicular hyaluronidase was developed. This consisted of two steps: (i) chromatography on dermatan sulphate-substituted AH-Sepharose 4B; (ii) chromatography on acetylated AH-Sepharose 4B. This procedure gave hyaluronidase with a specific activity of 19.1 units (mumol/min)/mg in high yield. Polyacrylamide-gel electrophoresis at pH 4.3 revealed two components, both possessing hyaluronidase activity. Sodium dodecyl sulphate polyacrylamide-gel electrophoresis likewise revealed two close bands with approximate molecular weights of 61000 and 67200.
The conversion of human complement component C5 into fragment C5b by the alternative-pathway C5 convertase
Authors: DiScipio R G
Published: August 2015

The cleavage of human complement component C5 to fragment C5b by the alternative pathway C5 convertase was studied. The alternative-pathway C5 convertase on zymosan can be represented by the empirical formula zymosan--C3b2BbP. Both properdin-stabilized C3 and C5 convertase activities decay with a half life of 34 min correlating with the loss of the Bb subunit. The C5 convertase functions in a stepwise fashion: first, C5 binds to C3b and this is followed by cleavage of C5 to C5b. The capacity to bind C3b is a stable feature of component C5, as C5b also has this binding capacity. Component C5, unlike component C3, does not form covalent bonds with zymosan after activation, and C5 is not inhibited by amines. Therefore C5, although similar in structure to C3, does not appear to contain the internal thioester group reported for C3 and C4.
Receptor-mediated vitellogenin binding to chicken oocytes
Authors: Yusko S , Roth T F , Smith T
Published: August 2015

The specific binding of vitellogenin to chicken oocyte membranes was characterized. This major hen serum phospholipoglycoprotein and one of its lower-molecular-weight components, phosvitin, bound to oocyte membranes with KD values of approx. 6 x 10-7 M. The optimum pH for binding was 6.0, the same as the pH of yolk contents. Phosvitin and vitellogenin compete with each other for binding; other proteins tested do not compete to the same degree. Phosvitin, which contains 10% phosphate by weight, appears to be the polypeptide recognized by the receptor. RNA failed to compete with either vitellogenin or phosvitin for binding, suggesting that the binding specificity may require more than polymeric phosphate. The binding was tissue-specific in that phosvitin and vitellogenin bound to oocyte surfaces (at both pH 6.0 and 7.5), but not to chicken erythrocytes (at either pH).
On the formation of amino acids deriving from spermidine and spermine
Authors: Seiler N , Knödgen B , Gittos M W , Chan W Y , Griesmann G , Rennert O M
Published: August 2015

Evidence obtained from experiments with rats and mice is presented suggesting that the naturally occurring amino acids putreanine and N8-(2-carboxyethyl)spermidine, and most probably also related compounds deriving from the polyamines spermidine and spermine by oxidative metabolism, are formed within two anatomical compartments. In the first step polyamines are converted into aldehydes by serum spermine oxidase in the circulation. A certain portion of these aldehydes can be taken up by liver and other organs and transformed by aldehyde dehydrogenase into the corresponding amino acids. Putreanine is not only derived from spermidine, but can also be formed from N8-(2-carboxyethyl)spermidine by oxidative deamination, catalysed by serum spermine oxidase, and subsequent spontaneous elimination of acrolein.
The hypothesis of localized chemiosmosis is unsatisfactory
Authors: Westerhoff H V , Simonetti A L M , Van Dam K
Published: August 2015

The hypothesis of ‘localized’ chemiosmosis have been put to an experimental test in the system of oxidative phosphorylation by rat liver mitochondria. We find that the variation of the ratio of phosphate potential to delta muH with delta muH does not depend on how delta muH is varied. This is in conflict with hypotheses of localized chemiosmosis. Of all coupling hypotheses, only the parallel-coupling hypothesis can explain the observations, unless variation of the H+/ATP stoichiometry of the ATPase proton pump is accepted. In the latter case. ‘macroscopic’ chemiosmosis can explain the observations equally well as hypotheses of localized chemiosmosis. It is concluded that either variation of H+/ATP stoichiometries must be accepted, or that the parallel-coupling hypothesis should be reformulated so that it becomes open to experimental tests.
Whole-cell uptake and nuclear localization of 1,25-dihydroxycholecalciferol by breast cancer cells (T47 D) in culture
Authors: Sher Elizabeth , Eisman John A. , Moseley Jane M. , Martin T. John
Published: August 2015

Specific high-affinity receptors for 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] have been described recently in broken-cell preparations of several cultured human breast cancer cell lines including the T47 D line. It was necessary to determine whether intact breast cancer cells in culture would bind 1,25-(OH)2D3 specifically and whether the next step in the proposed scheme of action, i.e. nuclear translocation, occurred. The following results were obtained. (1) Specific uptake of 1,25-(OH)2D3 by T47 D cells occurs in intact cells in culture. (2) The rate of uptake is proportional to medium 1,25-(OH)2D3 concentration but is slow compared with that of other steroid hormones, e.g., oestradiol, under identical conditions. Even at 0.5nm-1,25-(OH)2D3 in the medium, at least 4h are required to reach maximum compared with less than 1h for oestradiol binding. (3) Estimation of binding characteristics by Scatchard analysis indicates a single class of binding sites with Kd of 68pm and 11800 binding sites/cell, which are similar results to those obtained with broken-cell preparations. (4) Inclusion of various vitamin D metabolites in the incubation medium decreased specific binding of 1,25-(OH)2D3 by the intact cells in a manner identical with their effects in the broken-cell preparation and with potencies similar to their potency on Ca2+ transport and bone resorption in vivo. Order of potency was 1,25-(OH)2D3>(24R)-1,24,25-trihydroxycholecalciferol »25-hydroxycholecalciferol>(25R)-24,25-dihydroxycholecalciferol »(25R)-25,26-dihydroxycholecalciferol. (5) In the 1,25-(OH)2D3-depleted state, 80% of the 1,25(OH)2D3 receptor is found in the cytosol fraction of the cells even when the subcellular fractionation is performed under low-salt conditions. By contrast after incubation with [3H]1,25-(OH)2D3, 59% of the specific 1,25-(OH)2D3 binding is found in the partially purified nuclei fraction. These data indicate that nuclear translocation of the receptor–hormone complex takes place in the intact T47 D cell. The results also support the hypothesis that the 1,25-(OH)2D3 receptor is functional in this cultured breast cancer cell line, which may provide a useful model for further study of the early biochemical events in 1,25-(OH)2D3 action.
Labelling of membrane glycoproteins on rat spermatozoa collected from different regions of the epididymis
Authors: Jones R , Pholpramool C , Setchell B P , Brown C R
Published: August 2015

The major glycoprotein on the plasma membrane of testicular spermatozoa labelled with the galactose oxidase/NaB3H4 technique has mol.wt. 110 000. As spermatozoa pass through the epididymis, labelling of this glycoprotein disappears and is replaced by labelling of a 32 000-mol.wt. protein. The latter protein is a major component of epididymal secretions. The evidence suggests that it is inserted into or absorbed on to the plasma membrane, and since its appearance on spermatozoa correlates with the acquisition of fertilizing capacity it should serve as a good marker for assessing maturation in vitro.
Heterologous desensitization of the cyclic AMP-independent glycogenolytic response in rat liver cells
Authors: Bréant B , Keppens S , De Wulf H
Published: August 2015

Vasopressin and alpha-adrenergic agonists are known to be potent cyclic AMP-independent Ca2+-dependent activators of liver glycogen phosphorylase. When hepatocytes are pre-incubated with increasing concentrations of vasopressin or of the alpha-agonist phenylephrine, they become progressively unresponsive to a second addition of the respective agonist. The relative abilities of six vasopressin analogues and of five alpha-agonists to activate glycogen phosphorylase and to cause subsequent desensitization are highly correlated, indicating that the same vasopressin and alpha-adrenergic receptors are involved in both responses. About 5-times-higher peptide concentrations are needed to desensitize the cells than to activate their glycogen phosphorylase, whereas the concentrations of alpha-agonists required for the desensitization are only twice those needed for the activation of phosphorylase. The desensitization is not mediated by a perturbation in the agonist-receptor interaction. It is clearly heterologous, i.e. it is not agonist-specific, and must therefore involve a mechanism common to both series of agonists. The evidence for a role of Ca2+ movements or phosphatidylinositol turnover is briefly discussed.
Mitochondrial respiratory chain and thioredoxin reductase regulate intermembrane Cu,Zn-superoxide dismutase activity: implications for mitochondrial energy metabolism and apoptosis
Authors: Iñarrea Pedro , Moini Hadi , Han Derick , Rettori Daniel , Aguiló Ignacio , Alava Maria Angeles , Iturralde María , Cadenas Enrique
Published: August 2015

IMS (intermembrane space) SOD1 (Cu/Zn-superoxide dismutase) is inactive in isolated intact rat liver mitochondria and is activated following oxidative modification of its critical thiol groups. The present study aimed to identify biochemical pathways implicated in the regulation of IMS SOD1 activity and to assess the impact of its functional state on key mitochondrial events. Exogenous H2O2 (5 μM) activated SOD1 in intact mitochondria. However, neither H2O2 alone nor H2O2 in the presence of mitochondrial peroxiredoxin III activated SOD1, which was purified from mitochondria and subsequently reduced by dithiothreitol to an inactive state. The reduced enzyme was activated following incubation with the superoxide generating system, xanthine and xanthine oxidase. In intact mitochondria, the extent and duration of SOD1 activation was inversely correlated with mitochondrial superoxide production. The presence of TxrR-1 (thioredoxin reductase-1) was demonstrated in the mitochondrial IMS by Western blotting. Inhibitors of TxrR-1, CDNB (1-chloro-2,4-dinitrobenzene) or auranofin, prolonged the duration of H2O2-induced SOD1 activity in intact mitochondria. TxrR-1 inactivated SOD1 purified from mitochondria in an active oxidized state. Activation of IMS SOD1 by exogenous H2O2 delayed CaCl2-induced loss of transmembrane potential, decreased cytochrome c release and markedly prevented superoxide-induced loss of aconitase activity in intact mitochondria respiring at state-3. These findings suggest that H2O2, superoxide and TxrR-1 regulate IMS SOD1 activity reversibly, and that the active enzyme is implicated in protecting vital mitochondrial functions.
Postnatal changes in dolichol-pathway enzyme activities in cerebral cortex neurons
Authors: Idoyaga-Vargas V , Carminatti H
Published: August 2015

Neuronal perikarya were isolated from rat cerebral cortex at different stages of postnatal development. Membranes sedimenting at 100000 g were obtained from these neurons to study several glycosyltransferases of the dolichol pathway. Enzyme activities from stages before and during synapse formation were compared (days 5 and 15 respectively). Dolichyl diphosphate (Dol-P-P) N-acetylglucosamine, dolichyl phosphate mannose and dolichyl phosphate glucose synthases and the enzymes catalysing Dol-P-P-GlcNAc2Man9Glc3 formation were higher at day 15 of postnatal development. The glycosyl transfer of the latter compound to endogenous protein(s) as well as to a dinitrophenyl-heptapeptide was also measured. The activity was higher at day 15. Furthermore, the activity of dolichyl phosphate mannose synthase was also measured during the time when the number of synapses ceased to increase (day 36) and in the adult stage. The activity of dolichyl phosphate mannose synthase was higher at day 36 than at day 15, and declined in the adult stage. From these results it may be concluded that there is an increase in the glycosylation of asparagine-type glycoproteins during synapse formation in the neurons of the cerebral cortex.
Microvillar iron-binding glycoproteins isolated from the rabbit small intestine
Authors: O'Donnell M W , Cox T M
Published: August 2015

Rabbit intestinal microvillus membranes possess high-affinity receptors for iron whose activity reflects homeostatic changes in mucosal iron transport. To isolate and characterize these membrane components, purified microvilli were radiolabelled with 59Fe(II) and solubilized in Triton X-100. 59Fe in 105000g supernatants co-eluted with a major broad protein peak (Mr approx. 100000) on gel-permeation chromatography and was rendered diffusible by Pronase digestion but not mild periodate degradation. Fluorescence studies with castor-bean lectin conjugates showed specific binding of this affinity probe exclusively to brush-border membranes in the intestinal epithelium. Affinity chromatography of solubilized membrane proteins showed binding to columns of immobilized lectin. Elution with D(+)-galactose released glycoprotein-bound 59Fe purified up to sevenfold over initial membrane extracts. The lectin bound up to 82% of protein-bound 59Fe. In contrast polyspecific antisera raised against rabbit microvilli in guinea-pigs precipitated less than 10% of solubilized radioactivity. Significantly more protein-bound 59Fe in detergent extracts of microvilli purified from bled animals interacted specifically with the lectin, suggesting that membrane glycoprotein receptors are involved in the homeostatic control of intestinal iron transport.
Extensive destruction of newly synthesized casein in mammary explants in organ culture
Authors: Razooki Hasan Huthama , White David A. , Mayer R. John
Published: August 2015

1. Explants of mammary glands of mid-pregnant rabbits that had been cultured for 18h in the presence of insulin, prolactin and cortisol were incubated at 37°C for 2h in Medium 199 containing l-[4,5-3H]leucine. After a wash procedure at 4°C, explants were re-incubated at 37°C in fresh medium and the radioactivity of casein polypeptides isolated by isoelectric focusing (at pH 4.6) was followed with time. Casein radioactivity rose during the first hour of re-incubation, but fell markedly during the subsequent hour. 2. Loss of radioactivity represented casein degradation, since less than 10% of newly synthesized casein was found in the incubation medium. 3. Such a loss of radioactivity was not due solely to hydrolysis of signal peptides, since similar results were obtained when l-[5-3H]proline, which is not part of casein signal peptides, was the radiolabelled precursor. 4. A dual-isotope experiment using l-[U-14C]proline and N-[3H]acetyl-d-mannosamine gave similar profiles of radioactivity loss from isoelectrically focused casein, indicating that degradation of mature casein was occurring. 5. Analysis of total pellet and particle-free-supernatant fractions prepared by centrifugation of explant homogenates at 115000gav. for 1h did not show loss of radioactivity on re-incubation. Total pellet-protein radioactivity remained constant, whereas total soluble-protein radioactivity increased during the 2h re-incubation period. 6. Radioactivity in a specific particle-free-supernatant polypeptide, the subunit of fatty acid synthetase, mimicked that of the total soluble protein. 7. Addition of cycloheximide (20μg/ml) during the re-incubation period completely blocked the incorporation of radioactivity from l-[5-3H]proline into casein and the subsequent fall, indicating that observations were being made on newly synthesized casein. 8. Addition of chloroquine (50μm) did not prevent the increase in radioactivity from l-[5-3H]proline into casein during the first hour of re-incubation, but did prevent the loss of radioactivity in the second hour. 9. The intracellular degradation of a newly synthesized milk protein is discussed in relation to the known intracellular degradation of other secretory polypeptides.
Effects of protein-degradation inhibitors on the inactivation of tyrosine aminotransferase, tryptophan oxygenase and benzopyrene hydroxylase in isolated rat hepatocytes
Authors: Grinde B , Jahnsen R
Published: August 2015

The following three potent inhibitors of hepatocytic proteolysis were investigated to see if they would inhibit the intracellular inactivation of enzymes: chymostatin and leupeptin (proteinase inhibitors) and methylamine (a lysosomotropic weak base). Chymostatin inhibited the inactivation of two of the three enzymes tested: tyrosine aminotransferase (EC 2.6.1.5) and tryptophan oxygenase (tryptophan 2,3-dioxygenase, EC 1.13.11.11). Leupeptin had no effect on any of the enzymes, whereas methylamine had only a weak inhibitory effect on tyrosine aminotransferase inactivation. Apparently proteolytic cleavage (probably by a non-lysosomal proteinase, since only chymostatin is effective) is involved in the inactivation of tyrosine aminotransferase and tryptophan oxygenase. The third enzyme, benzopyrene hydroxylase (flavoprotein-linked mono-oxygenase, EC 1.14.14.1), is probably inactivated by a non-proteolytic mechanism.
Polyamines in mycoplasmas and in mycoplasma-infected tumour cells
Authors: Alhonen-Hongisto L , Veijalainen P , Ek-Kommonen C , Jänne J
Published: August 2015

Three out of four different mycoplasma strains analysed for the polyamine contents contained relatively high concentrations of putrescine, cadaverine, spermidine and spermine. In addition to ornithine decarboxylase (EC 4.1.1.17) activity, the mycoplasmas also exhibited comparable or higher lysine decarboxylase (EC 4.1.1.18) activity fully resistant to the action of 2-difluoromethylornithine, an irreversible inhibitor of eukaryotic ornithine decarboxylase. 2-Difluoromethylornithine did not modify the polyamine pattern of actively growing mycoplasmas. Ehrlich ascites carcinoma cells and L1210 mouse leukemia cells infected with any of the four mycoplasma strains contained, in addition to putrescine, spermidine and spermine, and also easily measurable concentrations of cadaverine; the latter diamine was absent in uninfected cultures. When the infected cells were exposed to difluoromethylornithine, the accumulation of cadaverine was markedly enhanced. The modification of cellular polyamine pattern by mycoplasmas, especially in the presence of inhibitors of eukaryotic ornithine decarboxylase, could conceivably be used as an indicator of mycoplasma infection in cultured animal cells.
The role of lysosomes in exercise-induced hepatic protein loss
Authors: Kasperek G J , Dohm G L , Barakat H A , Strausbauch P H , Barnes D W , Snider R D
Published: August 2015

Previous reports have shown that exercise causes a loss of liver protein. The purpose of the present study was to elucidate the mechanism of this exercise-induced protein loss. Exercise caused: (1) an increase in mechanical and osmotic lysosomal fragility; (2) a significant loss of hepatic water, glycogen, protein, phospholipid and RNA; (3) loss of protein from the soluble, mitochondrial and microsomal fractions: (4) loss of mitochondrial, microsomal and cytosolic, but not lysosomal, enzyme activity; (5) an increase in the number of autophagic vacuoles; (6) an increase in the lysosomal size. Taken together, these results suggest that the autophagolysosomal system is responsible for the exercise-induced hepatic protein loss.
Copper metabolism in mottled mouse mutants. The effect of copper therapy on lysyl oxidase activity in brindled (Mobr) mice
Authors: Royce P M , Camakaris J , Mann J R , Danks D M
Published: August 2015

Lysyl oxidase activity in extracts of skin from 1-day-old Mobr/Y mice was found to be between 50 and 60% of that in corresponding extracts from littermate +/Y mice of the same age. It was increased to 84-150% of that in the latter by prior treatment of the Mobr/Y mice at 7 days of age with a single subcutaneous injection of 50 micrograms of copper, retained as Cu+ in an alkyl polyether/sebacic acid solution. This suggests that in this form the copper is able to by-pass the block in copper metabolism and is deliverable to copper-requiring processes.
Progesterone therapy results in partial reversibility of uterine abnormalities of the adult anovulatory rat
Authors: White J O , Moore P A , Elder M G , Lim L
Published: August 2015

The effects of progesterone therapy (5 mg, administered subcutaneously daily for 6 days) on the abnormal uterus of adult anovulatory Wistar rats have been studied. These rats, rendered anovulatory by neonatal treatment with testosterone propionate or clomiphene citrate, displayed severe hyperplasia and metaplasia of the uterine luminal epithelium and a disproportionately high content of nuclear oestrogen receptor, as a result of constant oestrogen stimulation unrelieved by progesterone [White, Moore, Elder & Lim (1981) Biochem. J. 196, 557-565]. Progesterone therapy resulted in the virtual elimination of the hyperplasia and metaplasia and a corresponding decrease in the content of nuclear oestrogen receptor with the proportion of the unoccupied nuclear receptor being increased to values exhibited by normal cyclic females. There was also a decrease in the content of progestin receptors, a putative index of oestrogenic stimulation. Further, in the testosterone-treated group, progesterone therapy resulted in the restoration of oestrogen receptor translocational responses to oestradiol stimulation. Progesterone treatment of these anovulatory rats thus provides a model system for investigating the biochemical mechanisms underlying progestin antagonism and regulation of oestrogen-stimulated cell proliferation.
Evidence for a mechanism for the initiation of acid hydrolase secretion by macrophages that is functionally independent of alternative pathway complement activation
Authors: Riches D W H , Stanworth D R
Published: August 2015

A mechanism for the initiation of selective acid hydrolase secretion with macrophages by weak bases that is functionally independent of complement activation is proposed on the basis of the following findings. (1) The release of beta-galactosidase from macrophages exposed to methylamine and chloroquine was found to be highly dependent on the pH of the incubation medium; the degree of lysosomal secretion correlated closely with the amount of free base in solution at each pH investigated. (2) The secretion of beta-galactosidase induced by methylamine was additively enhanced by a fixed dose of zymosan; likewise, chloroquine additively enhanced the secretion of beta-galactosidase during exposure to zymosan. By contrast, chloroquine did not additively enhance the release of lysosomal enzyme affected by exposure to methylamine. (3) Two new secretagogues, imidazole and benzamidine, like chloroquine, failed to initiate any activation of the alternative complement pathway. The possible relationship between secretagogue induced vacuolization and lysosomal secretion is discussed.
Primary structure of major outer-membrane protein I (ompF protein, porin) of Escherichia coli B/r
Authors: Chen R , Krämer C , Schmidmayr W , Chen-Schmeisser U , Henning U
Published: August 2015

In the outer membrane of Gram-negative bacteria hydrophilic pores exist, allowing the diffusion of various low-molecular-weight solutes. These pores are formed by proteins, the porins. In a preliminary communication [Chen, Krämer, Schmidmayr & Henning (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 5014-5017] we presented the primary structure of one of these porins, the 340-amino-acid-residue protein I (ompF protein) from Escherichia coli B/r. In the present paper we give the experimental evidence for this sequence. Two tryptophan positions, one valine position, two aspartic acid positions and nine out of 82 amide determinations have been corrected. To aid further studies on this class of transmembrane proteins, the isolation of most of the constituent peptides is documented.
Rat mammary-gland fatty acid synthase. A simple purification procedure and stoicheiometry of CoA ester binding
Authors: Ahmad P M , Feltman D S , Ahmad F
Published: August 2015

A simple procedure was devised which allows purification of rat lactating-mammary-gland fatty acid synthase to a high degree of purity, with recoveries of activity exceeding 50%. Over 50 mg of enzyme was isolated from 60 g of mammary tissue. The specific activity of the purified enzyme was about 2.5 mumol of NADPH oxidized/min per mg of protein at 37 degrees. The enzyme appeared homogeneous by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and by immunodiffusion analysis. Each mol (Mr 480 000) of the enzyme bound 3 mol of acetyl and 3-4 mol of malonyl groups when the binding experiments were performed at 0 degrees for 30 s. The presence of NADPH did not influence the binding stoicheiometry for these acyl-CoA derivatives. Approx. 2 mol of taurine was found per mol of the performic acid-oxidized enzyme, suggesting that there were 2 mol of 4′-phosphopantetheine in the native enzyme. Rat mammary-gland fatty acid synthase required free CoA for activity.
The SalGI restriction endonuclease. Mechanism of DNA cleavage
Authors: Maxwell A , Halford S E
Published: August 2015

The cleavage of supercoiled DNA of plasmid pMB9 by restriction endonuclease SalGI has been studied. Under the optimal conditions for this reaction, the only product is the linear form of the DNA, in which both strands of the duplex have been cleaved at the SalGI recognition site. DNA molecules cleaved in one strand at this site were found to be poor substrates for the SalGI enzyme. Thus, both strands of the DNA appear to be cleaved in a concerted reaction. However, under other conditions, the enzyme cleaves either one or both strands of the DNA; the supercoiled substrate is then converted to either open-circle or linear forms, the two being produced simultaneously rather than consecutively. We propose a mechanism for the SalGI restriction endonuclease which accounts for the reactions of this enzyme under both optimal and other conditions. These reactions were unaffected by the tertiary structure of the DNA.
Isolation and characterization of β- and γ-caseins from horse milk
Authors: Visser S , Jenness R , Mullin R J
Published: August 2015

Three groups of casein components were isolated from horse milk. Group I is almost insoluble at acid and neutral pH, and is rather heterogeneous on alkaline gels with or without sodium dodecyl sulphate. Group II shows strong similarity to beta-casein from other species, as concluded from its amino acid composition and its N- and C-terminal sequences. This group consists of five electrophoretically distinguishable forms, all containing ester phosphate groups but no carbohydrate. Group III is composed of C-terminal fragments of the beta-like (group II) fraction and probably arises from the action of a plasmin-like enzyme present in horse milk. It does not contain phosphate or carbohydrate. Homology of this group with bovine gamma-caseins is demonstrated. Both beta- and gamma-like caseins are more soluble at 4 degrees C than at room temperature.
Cytochrome P-450 induction by clofibrate. Purification and properties of a hepatic cytochrome P-450 relatively specific for the 12- and 11-hydroxylation of dodecanoic acid (lauric acid)
Authors: Gibson G. Gordon , Orton Terry C. , Tamburini Paul P.
Published: August 2015

Hypolipidaemic drugs induce peroxisomal proliferation in the liver and many induce the formation of the hepatic endoplasmic reticulum in general and the formation of cytochrome P-450 in particular. We have induced the formation of rat liver microsomal cytochrome P-450 by the administration of the hypolipidaemic drug clofibrate, isolated the endoplasmic reticulum, solubilized the cytochrome P-450 from these membranes and subdivided the cytochrome P-450 into four fractions by the use of hydrophobic, anionic, cationic and adsorption chromatography. One of these fractions (cytochrome P-450 fraction 1) was highly purified to a specific content of 17nmol of cytochrome P-450/mg of protein and the protein was active in a reconstituted enzyme system towards the 12- and 11-hydroxylation of the fatty acid, dodecanoic (lauric) acid, with preferential activity towards the 12-hydroxy metabolite. This reconstituted activity was absolutely dependent on NADPH, NADPH-cytochrome P-450 reductase and cytochrome P-450, indicating the role of the mixed-function oxidase system in the metabolism of lauric acid. Another fraction of the haemoprotein (cytochrome P-450 fraction 2) preferentially formed 11-hydroxylauric acid, whereas a third fraction (cytochrome P-450 fraction 3) exhibited only trace laurate oxidase activity and was similar to the phenobarbitone form of the haemoprotein in that these last two cytochromes rapidly turned-over the drug benzphetamine. The molecular weights and spectral properties of these cytochrome P-450 fractions are reported, along with the phenobarbitone-induced form of the enzyme and the nature of the cytochrome(s) induced by clofibrate pretreatment are discussed in the terms of possible haemoprotein heterogeneity.
Structural features of the first component of human complement, C1, as revealed by surface iodination
Authors: Villiers C L , Chesne S , Lacroix M B , Arlaud G J , Colomb M G
Published: August 2015

Lactoperoxidase-catalysed surface iodination and sucrose-gradient ultracentrifugation were used to investigate the structure of human complement component C1. 1. Proenzymic subcomponents C1r and C1s associated to form a trimeric C1r2-C1s complex (7.6 S) in the presence of EDTA, and a tetrameric Clr2-C1s2 complex (9.1 S) in the presence of Ca2+. Iodination of the 9.1 S complex led to a predominant labelling of C1r (70%) over C1s (30%), essentially located in the b-chain moiety of C1r and in the a-chain moiety of C1s. 2. Reconstruction of proenzymic soluble C1 (15.2 S) from C1q, C1r and C1s was partially inhibited when C1s labelled in its monomeric form was used and almost abolished when iodinated C1r was used. Reconstruction of fully activated C1 was not possible, whereas hybrid C1q-C1r2-C1s2 complex was obtained. 3. Iodination of proenzymic or activated C1 bound to IgG-ovalbumin aggregates led to an equal distribution of the radioactivity between C1q and C1r2-C1s2. With regard to C1q, the label distribution between the three chains was similar whether C1 was in its proenzymic or activated form. Label distribution in the C1r2-C1s2 moiety of C1 was the same as that obtained for isolated C1r2-C1s2, and this was also true for the corresponding activated components. However, two different labelling patterns were found, corresponding to the proenzyme and the activated states.
Structurally inherent antigenic sites. Localization of the antigenic sites of the α-chain of human haemoglobin in three host species by a comprehensive synthetic approach
Authors: Kazim A L , Atassi M Z
Published: August 2015

The antigenic structure of the alpha-chain of human haemoglobin was studied by a synthetic approach consisting of the synthesis of a series of consecutive overlapping peptides that together systematically represent the entire primary structure of the protein. This approach enabled the identification of a full profile of immunochemically active alpha-chain peptides and the localization of its major ‘continuous’ antigenic sites. Antibodies to haemoglobin raised in each of three different species (goat, rabbit and mouse) recognize similar sites on the alpha-chain. Further, the molecular locations of these sites coincide with alpha-chain regions extrapolated from antigenic sites of the conformationally similar myoglobin molecule. These findings support our earlier proposed concept of ‘structurally inherent antigenic sites’, namely that antigenicity is conferred on certain surface regions of proteins by virtue of their three-dimensional locations. Thus the antigenic sites of conformationally related proteins are likely to have similar molecular locations.
Titration and steady-state behaviour of the 830 nm chromophore in cytochrome c oxidase
Authors: Nicholls P , Chanady G A
Published: August 2015

Titration of cyanide-incubated cytochrome c oxidase (ox heart cytochrome aa3) with ferrocytochrome c or with NNN'N'-tetramethyl-p-phenylenediamine initially introduces two reducing equivalents per mol of cytochrome aa3. The first equivalent reduces the cytochrome a haem iron; the second reducing equivalent is not associated with reduction of the 830 nm chromophores (e.p.r.-detectable copper) but is probably required for reduction of the e.p.r.-undetectable copper. Excess reductant introduces a third reducing equivalent into the cyanide complex of cytochrome aa3. During steady-state respiration in the presence of cytochrome c and ascorbate, the 830 nm chromophore is almost completely oxidized. It is reduced more slowly than cytochrome a on anaerobiosis. In the presence of formate or azide, some reduction at 830 nm can be seen in the steady state; in an oxygen-pulsed system, a decrease in steady-state reduction of cytochromes c and a is associated with ab increased reduction of the 830 nm species. In the formate-inhibited system the reduction of a3 on anaerobiosis shows a lag phase, the duration of which corresponds to the time taken for the 830 nm species to be reduced. It is concluded that the e.p.r.-undetectable copper (CuD) is reduced early in the reaction sequence, whereas the detectable copper (CUD) is reduced late. The latter species is probably that responsible for reduction of the cytochrome a3 haem. The magnetic association between undetectable copper and the a3 haem may not imply capability for electron transfer, which occurs more readily between cytochrome a3 and the 830 nm species.