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PubMed1982

Divergence of the two albumins of X. laevis. Evidence for the glycosylation of the major 74K albumin.

The mRNAs coding for the 68,000 and 74,000 dalton serum albumins of Xenopus laevis were purified by hybridisation to their corresponding cloned cDNA and translated using the reticulocyte lysate. The primary translational product of the 68,000 dalton albumin has a molecular weight of 70,000 daltons suggesting that it is synthesised with a signal peptide which is cleaved during secretion. In contrast, the primary translational product of the 74,000 dalton albumin has a molecular weight of 72,000 daltons suggesting that it must be posttranslationally modified to account for the increased molecular weight of the mature protein. X. laevis oocytes injected with albumin mRNA secrete proteins of the same molecular weights as the mature albumins. When these translational products were chromatographed on concanavalin A Sepharose, the 74,000 dalton albumin was bound suggesting that it is glycosylated. Comparison of X. laevis and X. tropicalis albumins suggests that the 68,000 dalton albumin is similar to the primitive Xenopus albumin and that since the genome duplication which occurred in X. laevis, differences have arisen in both the length and processing of the primary translational product to account for the current difference in the molecular weights of the two X. laevis albumins.

Animals↗
PubMed1982

The renal clearance of albumin following intravenous loading of homologous albumin in conscious rats.

Tubular reabsorption of albumin was studied in conscious rats by measuring the renal excretion at various plasma concentrations. The plasma albumin concentration was raised by loading the animals with homologous serum albumin. By using this procedure an average plasma concentration of 54 g/l could be reached, which is about twice the physiological plasma albumin concentration in untreated rats. Throughout the experiments the glomerular filtration rate was determined by the total plasma slope clearance of 51Cr-EDTA. Following the albumin load, the 51Cr-EDTA clearance remained at 54.8 +/- 12.2 ml/min/m2 body surface. By correlating renal albumin excretion and plasma albumin concentration, the sieving coefficient of albumin, phi, of 2.35 x 10(-4), the renal albumin threshold of 38 +/- 5 g/l, and the maximal tubular transport rate of albumin of 9.6 +/- 2.6 micrograms/min/g kidney weight could be calculated (mean +/- SD). There were some variations among the animals, resulting in a fairly large standard deviation. However, these values are in agreement with recent micropuncture data.

Animals↗
PubMed1992

Preferential interaction of albumin-binding proteins, gp30 and gp18, with conformationally modified albumins. Presence in many cells and tissues with a possible role in catabolism.

Albumin binding to the endothelial surface apparently initiates its transcytosis via plasmalemmal vesicles and also increases capillary permselectivity. Several albumin-binding proteins, which, we call gp60, gp30, and gp18, have been identified; however, their functional relationship to each other is unclear. In this study, we show that gp30 and gp18 are both variably expressed by cultured rat fibroblasts, smooth muscle cells, and endothelial cells and are present in all tissues examined (heart, lung, skeletal muscle, diaphragm, duodenum, kidney, fat, brain, adrenal, pancreas, and liver). The binding of albumin-gold complexes (A-Au) to gp30 and gp18 was compared with that of native and modified albumins. Monomeric native bovine serum albumin (BSA) interacted much less avidly than A-Au and BSA that was chemically modified by formaldehyde (Fm-BSA) or maleic anhydride (Mal-BSA). Mal-BSA and A-Au have similar affinity constants for gp30 and gp18 (KD approximately 3-7 micrograms/ml (50-100 nM)), which is 1000-fold greater than BSA. These interactions were Ca(2+)-independent but sensitive to pH (< 6.0) and high salt concentrations (> or = 1.0 M). Comparative biochemical characterization provided evidence of conformational changes for Mal-BSA, Fm-BSA, and A-Au. Anti-native BSA serum recognizes BSA much more avidly than modified BSA. Mal-BSA, Fm-BSA, and A-Au are much more sensitive to trypsin digestion than BSA. Cellular processing was also examined. A-Au and Mal-BSA bound at the endothelial cell surface were degraded, whereas BSA was not. Our results indicate that: (i) gp30 and gp18, unlike gp60, are expressed in all tissues tested regardless of the type of endothelia lining the microvasculature and the local mechanism of transendothelial albumin transport; (ii) BSA conformationally modified by either surface adsorption or chemical means not only interacts more avidly with gp30 and gp18 than native albumin but also is preferentially degraded by the cells; (iii) A-Au and native albumin are not equivalent probes for detecting albumin interaction sites; and (iv) gp30 and gp18 exhibit binding behavior resembling scavenger receptors. The possible roles of gp30 and gp18 in albumin binding, transcytosis, endocytosis, and even protein catabolism are discussed.

Animals↗
PubMedDate not supplied

Binding properties of glycosylated albumin and acetaldehyde albumin.

Glucose and acetaldehyde react covalently with albumin to form the post-translationally modified group of proteins, the glycosylated albumins and the acetaldehyde albumins, respectively. This study contrasts the binding ability of a major acetaldehyde albumin fraction synthesized in vitro with glycosylated albumin. A microdialysis rate method, using either [14C]monoacetyldiaminodiphenyl sulfone (MADDS), a deputy ligand for bilirubin, or [14C]diazepam, was employed to evaluate binding at these two sites. Our results indicate that prolonged exposure of purified human serum albumin to acetaldehyde results in a major acetaldehyde albumin fraction that lacks the ability to bind MADDS and diazepam. This fraction migrates identically to albumin on SDS polyacrylamide gel electrophoresis, but exhibits microheterogeneity with a more acidic pI band as seen on analytical isoelectric focusing. We suggest that altered drug binding in alcoholics may be partially explained by altered binding ability of acetaldehyde albumins.

Acetaldehyde↗
PubMed1991

The effect of varying albumin concentration and hydrostatic pressure on hydraulic conductivity and albumin permeability of cultured endothelial monolayers.

An in vitro model of the endothelial transport barrier was developed using bovine aortic endothelial cell monolayers cultured on a porous polycarbonate substrate. Hydraulic conductivity (Lp) was measured by a bubble tracking technique at varying pressure differentials and albumin concentrations. The effective albumin permeability (Pc) was determined by measuring the flux of fluorescent-labeled albumin across monolayers at varying hydrostatic pressures. Lp determined at pressure differentials between 5.0 and 10 cm H2O demonstrated a strong dependence on albumin concentration, decreasing approximately 10-fold from 21.3 x 10(-7) +/- 3.18 x 10(-7) cm/sec/cm H2O (mean +/- SEM) at 0.0 g/dl to 2.35 x 10(-7) +/- 0.20 x 10(-7) cm/sec/cm H2O at 1.0 g/dl albumin. Increasing the albumin concentration from 1.0 to 4.0 g/dl reduced Lp by an additional 16% to 1.97 x 10(-7) +/- 0.17 x 10(-7) cm/sec/cm H2O. Furthermore, Lp was moderately dependent on the pressure differential, increasing by about a factor of two with a doubling of the pressure differential. The effective permeability (Pc) was also dependent on the pressure differential. At an albumin concentration of 4.0 g/dl, Pc increased from 1.37 x 10(-6) +/- 0.26 x 10(-6) cm/sec at 0.0 cm H2O to 5.06 x 10(-6) +/- 1.92 x 10(-6) cm/sec at 10 cm H2O. Analysis of Pc and Jv data, however, demonstrates that water and albumin do not share a common pathway in crossing the endothelial monolayer. These data suggest the existence of a large pore pathway for albumin. Thus, the in vitro system has many of the transport characteristics of intact vessels in vivo and should be useful for physiological studies of the endothelial transport barrier.

Albumins↗
PubMed1983

Studies of albumin binding to rat liver plasma membranes. Implications for the albumin receptor hypothesis.

To characterize a previously proposed hepatocyte albumin receptor, we examined the binding of native and defatted 125I-labeled rat albumin to rat liver plasma membranes. After incubation for 30 min, binding was determined from the distribution of radioactivity between membrane pellet and supernatant following initial centrifugation (15000 X g for 15 min), and after repeated cycles of washing with buffer and re-centrifugation. 125I-labeled albumin recovered in the initial membrane pellet averaged only 4% of that incubated. Moreover, this albumin was only loosely associated with the membrane, as indicated by recovery in the pellet of under 0.5% of the counts after three washes. Binding of 125I-labeled albumin to the plasma membranes was no greater than to erythrocyte ghosts, was not inhibited by excess unlabeled albumin, and was not decreased by heat denaturation of the membranes, all suggestive of a lack of specific binding. Failure to observe albumin binding to the membranes was not due to a rapid dissociation rate or 'off-time', as incubations in the presence of sufficient ultraviolet light to promote covalent binding of ligands to receptors did not increase 125I counts bound to the membrane. Finally, affinity chromatography over albumin/agarose gel of solubilized membrane proteins provided no evidence of a membrane protein with a high affinity for albumin. These studies, therefore, do not support the hypothesis that liver cell plasma membranes contain a specific albumin receptor.

Animals↗
PubMed1983

Interstitial albumin mass and transcapillary extravasation rate of albumin in DMBA-induced rat mammary tumours.

Transcapillary extravasation rate for radio-iodinated human serum albumin (I-HSA) from plasma to interstitial fluid, interstitial albumin mass and interstitial albumin concentration have been determined in dimethyl-benz-alpha-anthracene (DMBA)-induced mammary tumours in rats. The plasma radioactivity of tracer was kept constant in awake, freely moving rats by a continuous infusion of I-HSA from 1 to 72 h after an initial priming dose. Capillary leakiness for I-HSA was calculated as the plasma equivalent volume of I-HSA located extravascularly after 1 h infusion divided by the blood volume in the tissue, i.e. as the fractional extravasation rate (FER). The experiments showed that FER was highest in tumours while intestine and skin had FER of about 70% and 25% that of tumour respectively. Heart and skeletal muscle had similar FER about 1/8 that of tumour. Interstitial albumin concentration in tumour averaged 42% of plasma albumin concentration in tumour. Intestine, heart and skeletal muscle had interstitial albumin concentrations between 34 and 37% of plasma albumin concentration while skin had an albumin concentration averaging 20% that of plasma. Lymph flow was calculated as the product of the fractional turnover rate constant for interstitial albumin and interstitial volume (extravascular 51Cr-EDTA volume) and averaged 36.7 X 10(-3) mg/g X h in tumour while intestine and heart had lymph flows of 19.1 X 10(-3) and 14.1 X 10(-3) ml/g X h respectively. In muscle and skin lymph flow was 2.4 X 10(-3) and 18.3 X 10(-3) ml/g X h respectively. It is suggested that the high interstitial fluid pressure previously observed in these tumours will contribute in maintaining interstitial volume in a steady state by opposing fluid filtration into the interstitium and maintaining a lymph flow high enough to remove excess fluid and protein from the interstitium.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Electrophoretic and chromatographic differentiation of two forms of albumin in equilibrium at neutral pH: new screening techniques for determination of ligand binding to albumin.

Analysis of normal human serum by crossed hydrophobic interaction immunoelectrophoresis with Phenyl-Sepharose revealed a biphasic appearance of the albumin peak. The molecular mechanism behind this apparent albumin heterogeneity was investigated. Analysis of defatted purified albumin showed that a major fraction bound to the Phenyl-Sepharose and that addition of ligands (e.g. long-chain fatty acids, bilirubin, sulfonamides and warfarin) before electrophoresis blocked this binding to different degrees. A quantitative relation between ligand binding and the amount of nonbinding albumin was found. Thus the technique might be suitable for screening of ligand binding to albumin. Analysis of serum samples from newborns with hyperbilirubinemia revealed a positive correlation between the fraction of the nonretarded albumin and the bilirubin concentration. By chromatography on Phenyl-Sepharose, defatted albumin was separated into a binding and a nonbinding form and this technique was subsequently used to determine the kinetics of the intramolecular conversion. After rechromatography, each of the fractions could again be separated into two fractions, indicating the presence of an equilibrium. By varying the passage time for albumin on the column or varying the period between the first and the second separation it was possible to calculate the conversion rates. The half-life for the conversion was found to be as long as 1 1/4 h. It is the first time that a conformational change for albumin with such a long conversion time has been described experimentally.

Bilirubin↗
PubMed1982

A comparative study of some physico-chemical properties of human serum albumin samples from different sources--I. Some physico-chemical properties of isoionic human serum albumin solutions.

Human serum albumin samples from different sources were investigated. The fatty acid content of the albumin before and after deionization on a mixed bed ion-exchange column varied from sample to sample. When an albumin sample from one source was deionized under standard conditions the amount of fatty acid bound by the albumin was reduced to a reproducible amount. In samples from different sources, however, the amount bound varied considerably. Also the isoionic pH of the albumin varied from sample to sample. This variation could be attributed to the difference in the fatty acid content and the different number of titratable histidines and acid amino-acid residues in the albumin from different sources. It can be concluded from the specific conductance of these isoionic solutions that ions other than H-, OH and protein are effectively removed by a mixed bed ion-exchange column. The specific conductance of the albumin samples is directly related to the isoionic pH. Therefore, the isoionic pH and the specific conductance of the albumins reflect the heterogeneity of the albumin samples with respect to their primary structure and fatty acid content.

Chemical Phenomena↗
PubMed1989

Mechanism by which warfarin binds to human serum albumin. Stopped-flow kinetic experiments with two large fragments of albumin.

In order to obtain information about the kinetics of the process by which warfarin binds to human serum albumin at a molecular level, we performed stopped-flow kinetic experiments on albumin and on a large peptic fragment (residues 1-387) and a large tryptic fragment (residues 198-585) of albumin. From these experiments it can be concluded that the first interaction between warfarin and the proteins is almost certainly diffusion-controlled and is dependent on the net charges of the reactants. The next step in the binding process involves the formation of an activated warfarin-protein complex, whereafter the final complex is formed. The warfarin-albumin complex forms more slowly than the warfarin-fragment complexes, because the formation is sterically hindered by the albumin structure. We think it very unlikely that albumin has an oblate ellipsoid structure; it is much more likely to have a U-shaped structure, where the domains make contact with each other. If this hypothesis is correct, then this indicates that the domains do not act independently of each other. The formation of the activated warfarin-albumin complex is further influenced by the conformational state of the albumin molecule, i.e. the N-B transition. The possible role of this N-B transition in albumin-mediated transport of drugs through cellular membranes is discussed.

Humans↗
PubMed1975

Evidence for the coupling of biosynthesis and secretion of serum albumin in the rat. The effect of colchicine on albumin production.

1. By using isotopic-dilution techniques it was found that colchicine causes a slight increase in the proalbumin content of liver, from 0.63+/-0.06 to 0.83+/-0.10mg/g of liver, but has no effect on albumin content (0.50+/-0.05mg/g of liver). All the proalbumin and 67% of the albumin is found in vesicles from which they are liberated by detergents. 2. Colchicine inhibits secretion of albumin, decreases the rate of conversion of proalbumin into albumin and decreases the rate of incorporation of l-[1-(14)C]leucine into proalbumin. 3. Balance studies in vivo show that all the (14)C appearing in serum albumin can be accounted for by the flow of (14)C through the proalbumin, in the presence or absence of colchicine. 4. When cycloheximide is given to the rats, 2min after [(14)C]leucine, further synthesis of protein stops. The label in proalbumin disappears and the proalbumin content of the liver falls, so as to account for the albumin appearing in the plasma. This occurs both in the presence and in the absence of colchicine. By contrast, there is little change in liver albumin. Studies with isolated perfused livers are in agreement with the above. Lumicolchicine has no effect on any of these systems at doses at which colchicine exerts its action. 5. These results suggest that biosynthesis and conversion of proalbumin into albumin, and secretion of serum albumin are controlled at each step.

Amino Acids↗
PubMed1996

Cross-antigenicity of horse serum albumin with dog and cat albumins: study of three short peptides with significant inhibitory activity towards specific human IgE and IgG antibodies.

Horse serum albumin is present in the near vicinity of the animal, while dog and cat serum albumins are very common allergens present in house dust. Human patients clinically defined as allergic to horse could react with horse serum albumin by means of IgE or IgG antibodies. Studies regarding the specificities of these antibodies by inhibition enzyme-linked immunosorbent assay (ELISA) and depletion experiments have demonstrated that they are directed against dog serum albumin and cross-react not only with horse serum albumin but with other serum albumins from different origins. To investigate these observations further, we isolated and characterized three tryptic peptides (P1, P2 and P3) from horse serum albumin. The peptide P1 contains loops 1 and 2 of the first domain, P2 is derived from loop 4 of the second domain, and P3 contains the disulphide loop 9 of the third domain. These were able to inhibit the binding of the patients' IgE and IgG antibodies to horse albumin as well as to dog and cat serum albumins. This indicates that these peptides are involved in the observed cross-reactions. They also shared common epitopes, as revealed by human IgE antibodies. After reduction and alkylation, they totally lost their inhibitory capacity, suggesting that the intra-chain disulphide bridges, essential for the preservation of the loop structure, probably maintain their allergenic/antigenic reactivity.

Allergens↗
PubMed2002

Predicting the decrease of conjugated bilirubin with extracorporeal albumin dialysis MARS using the predialysis molar ratio of conjugated bilirubin to albumin.

Extracorporeal albumin dialysis with the molecular adsorbent recirculating system (MARS) machine is a new supportive intervention for patients with liver failure. It removes bilirubin and other albumin-bound toxins from the patient and has been shown by preliminary studies of liver failure patients to be beneficial. Our study examines the ability of predialysis molar ratio of bilirubin to albumin to predict the decrease of bilirubin by MARS. We had 5 patients and results from 29 treatments. The results showed a significant correlation between the predialysis molar ratio of bilirubin (total and conjugated) to albumin to the reduction in bilirubin (total and conjugated): R(2) = 0.27 and 0.62 respectively, P <.005 for both. There was no significant correlation with the predialysis molar ratio of unconjugated bilirubin to albumin to the reduction in unconjugated bilirubin. The ratio of change in total bilirubin (micromol/L) to the predialysis molar ratio of total bilirubin to albumin and the ratio of change in conjugated bilirubin (micromol/L) to the predialysis molar ratio of conjugated bilirubin to albumin were 6.2 (+/- 4.2) and 10.8 (+/- 4.3), respectively (mean (+/- SD)). The results enable us to predict the likely reduction in bilirubin (especially conjugated) after each MARS treatment and also suggest to us that albumin infusion before MARS treatment may reduce the efficacy of bilirubin removal. Whether this ratio applies to other albumin-bound toxins remains open for investigation.

Bilirubin↗
PubMed1986

A sensitive routine assay for urinary albumin based on the competitive binding to anti-albumin antibodies in solid phase.

The detection of microalbuminuria has a high prognostic value in diabetic patients with no symptoms of clinical nephropathy. Attention has been focused on the development of a simple, reproducible, specific, and, above all, sensitive method to detect albuminuria in the urine. The method is based on the competitive binding between albumin in the urine to be tested and a fixed amount of radiolabelled albumin to anti-albumin immunoglobulins in solid phase. The immunoglobulin C fraction of a rabbit anti-human albumin antiserum was left to coat highly adsorbent polystyrene microtitre tubes. While the aspecific tube binding was overcome by saturation with a solution of gelatine, increasing dilutions of standard albumin or the diluted urine samples to be tested were left to incubate with an equal volume of radiolabelled albumin at room temperature for 1 hour. The cold/hot albumin mixture was added to anti-albumin immunoglobulin-coated tubes, which had been repeatedly washed, and left to incubate. After washing, radioactivity was assessed. This assay has proved to be fast, simple and highly sensitive since it detects up to 25 ng of albumin per ml and is of value in large-scale screening for microalbuminuria in diabetic patients.

Albumins↗
PubMed1982

Presence of albumin mRNA precursors in nuclei of analbuminemic rat liver lacking cytoplasmic albumin mRNA.

Analbuminemic rats, which lack serum albumin, were previously found to have no albumin mRNA in the cytoplasm of the liver. In the present study, the existence of nuclear albumin mRNA precursors in the liver of analbuminemic rats was examined by RNA X cDNA hybridization kinetics. Albumin mRNA precursors were present in the nuclei of analbuminemic rat liver at almost normal levels, despite the absence of albumin mRNA from the cytoplasm. Nuclear RNA of analbuminemic rat liver was subjected to electrophoresis on 1% agarose gel in parallel with nuclear RNA of normal rat liver. RNA was transferred from the gel to diazobenzyloxymethyl-paper and hybridized to cloned cDNA. Several bands of putative albumin mRNA precursors were obtained with nuclear RNA of analbuminemic rat liver and some of them were indistinguishable from those of normal rat liver. Nuclear RNA of analbuminemic rats was hybridized to 3'-end-labeled cloned cDNA under the conditions of RNA excess and then digested completely with S1 nuclease and subjected to electrophoresis on polyacrylamide gel. By this technique, nuclear RNA that could hybridized to cDNA was found to have the albumin mRNA sequence in at least the 3' half of the mRNa that was covered by cloned cDNA. For comparison of the structures of the albumin genes of analbuminemic and normal rats, DNAs from rat livers of both types were digested completely with EcoRI, HindIII, and Pst I; the fragments were separated by electrophoresis on 1% agarose gel, transferred to nitrocellulose paper, and hybridized to cloned cDNA. The intensities of the corresponding bands and the digestion patterns of the analbuminemic and normal rat genes were indistinguishable. From these data, it is concluded that analbuminemic rats have a unique type of mutation(s) affecting albumin mRNA maturation.

Animals↗
PubMed1976

Effect of albumin and methylated albumin on the glucose permeability of lipid membranes.

The diffusion of glucose from phospholipid membranes has been measured in the presence of serum albumin or methylated serum albumin. At neutral pH, serum albumin enhanced the rate at which glucose diffused from liposomes containing more than a certain amount of lysolecithin. Net charge of the membrane is not important for the reaction, since positively charged membranes containing stearylamine showed almost the same reactivity as negatively charged liposomes containing dicetyl phosphate. Carboxylmethylated albumin showed enhancement of the diffusion rate of glucose from negatively but not from positively charged liposomes. The amount of methylated albumin required to affect liposomes was much smaller than the amount of albumin required to damage liposomes containing lysolecithin. Cholesterol incorporation suppressed the sensitivity of liposomes to both proteins, albumin and methylated albumin. The effect of temperature and fatty acid composition of phospholipids on the sensitivity of liposomes to proteins suggests the importance of the fluidity of the membrane, especially in the case of methylated albumin.

Binding Sites↗
PubMed1991

Albumin binding properties in relation to bilirubin and albumin concentrations during the first week of life.

In 19 non-jaundiced and 22 jaundiced neonates, the serum albumin and bilirubin concentrations were measured during the first week of life. Some of the neonates were followed longitudinally. The albumin binding properties were evaluated by determining the reserve albumin concentration for monoacetyldiaminodiphenyl sulphone (MADDS), a deputy ligand for bilirubin. The reserve albumin concentration for MADDS increased with postnatal age. The reason for this increase is still unexplained. There was an inverse relation between the bilirubin and the reserve albumin concentrations, but when the bilirubin concentration increased by 1 mumol/l, the reserve albumin concentration for MADDS decreased by only 0.2 mumol/l. This shows that the reserve albumin concentration for MADDS does not give a direct measure of the bilirubin binding ability of the serum albumin molecule. In spite of this, it is still possible that a low reserve albumin concentration for MADDS is a risk factor for bilirubin encephalopathy.

Bilirubin↗
PubMed1987

Albumin-coated polyester arterial prostheses: is xenogenic albumin safe?

This paper adds a new dimension to the series of studies concerned with the development of an albumin-coated polyester vascular prosthesis by addressing the question of the origin of the albumin. Previous experiments in dogs have used canine albumin-coated polyester arterial grafts. This study evaluated the biocompatibility of xenogenic material by implanting in dogs prostheses coated with bovine albumin and cross-linked with glutaraldehyde. Two series of albuminated grafts, one gamma radiation sterilized, the other ethylene oxide sterilized, as well as a preclotted control series were undertaken. The origin of the albumin did not appear to be significant. In fact, the healing pattern of the xenogenic albumin coated grafts was identical to that found previously with isogenic albumin. Nor did the method of sterilization produce significantly different pathological results. However, a slower rate of healing with the coated grafts compared to the preclotted controls did appear to be related to the slow rate of albumin erosion and the potentially cytotoxic effect of the glutaraldehyde cross-linking agent.

Albumins↗