Human fetal liver fatty acid binding proteins. Role on glucose-6-phosphate dehydrogenase activity.
03 Apr 1989-Biochimica et Biophysica Acta (Elsevier)-Vol. 1002, Iss: 2, pp 164-172
TL;DR: F fetal liver FABPs play a regulatory role in critical aspects of cellular physiology during human embryogenesis and protect glucose-6-phosphate dehydrogenase from the feed-back inhibition exerted by added palmitoyl-CoA and oleate.
Abstract: Fatty acid binding proteins (FABPs) may play an important role in the transport and metabolism of fatty acids during human embryogenesis. Three fractions of FABP, namely, DE-I, DE-II and DE-III, having Mr 14 200 Da each and pI values 7.8, 6.9 and 5.4, respectively, have been detected in human fetal liver. These proteins were purified by heat and butanol precipitation of fetal liver supernatant as well as by gel filtration and ion-exchange chromatography. Fetal liver FABPs are immunochemically identical to each other. Concentrations of DE-I, DE-II and DE-III increase gradually from early gestation to term. DE-I is almost lipid-free, DE-II binds long-chain fatty acids nonspecifically and DE-III transports mainly arachidonic acid. DE-II and DE-III protect glucose-6-phosphate dehydrogenase, which furnishes NADPH for fatty acid synthesis, from the feed-back inhibition exerted by added palmitoyl-CoA and oleate. In the absence of exogenous inhibitors, this enzyme is stimulated by FABPs. DE-I has no effect on such inhibition. Thus, FABPs play a regulatory role in critical aspects of cellular physiology during human embryogenesis.
TL;DR: Article de synthese sur les donnees recentes de caracteristiques structurales et physicochimiques de divers types of proteines de liaison aux acides gras, avec la signification physiologique de ces diversites.
Abstract: Article de synthese sur les donnees recentes de caracteristiques structurales et physicochimiques de divers types de proteines de liaison aux acides gras, avec la signification physiologique de ces diversites
TL;DR: A considerable body of indirect evidence is provided supporting a broad role for the FABP in the intracellular transport and metabolism of long-chain fatty acids and the existence of structure- and tissue-specific specialization of function among different members of the F ABP gene family.
Abstract: Cytosolic fatty acid binding proteins (FABP) belong to a gene family of which eight members have been conclusively identified. These 14–15 kDa proteins are abundantly expressed in a highly tissue-specific manner. Although the functions of the cytosolic FABP are not clearly established, they appear to enhance the transfer of long-chain fatty acids between artificial and native lipid membranes, and also to have a stimulatory effect on a number of enzymes of fatty acid metabolism in vitro. These findings, as well as the tissue expression, ligand binding properties, ontogeny and regulation of these proteins provide a considerable body of indirect evidence supporting a broad role for the FABP in the intracellular transport and metabolism of long-chain fatty acids. The available data also support the existence of structure- and tissue-specific specialization of function among different members of the FABP gene family. Moreover, FABP may also have a possible role in the modulation of cell growth and proliferation, possibly by virtue of their affinity for ligands such as prostaglandins, leukotrienes and fatty acids, which are known to influence cell growth activity. FABP structurally unrelated to the cytosolic gene family have also been identified in the plasma membranes of several tissues (FABPpm). These proteins have not been fully characterized to date, but strong evidence suggests that they function in the transport of long-chain fatty acids across the plasma membrane.
TL;DR: Which FABPs form biochemically defined or true isoforms versus FABP that form additional forms, operationally defined as isoforms, is critically evaluated.
Abstract: Although structural aspects of cytosolic fatty acid binding proteins (FABPs) in mammalian tissues are now well understood, significant advances regarding the physiological function(s) of these proteins have been slow in forthcoming. Part of the difficulty lies in the complexity of the multigene FABP family with nearly twenty identified members. Furthermore, isoelectric focusing and ion exchange chromatography operationally resolve many of the mammalian native FABPs into putative isoforms. However, a more classical biochemical definition of an isoform, i.e. proteins differing by a single amino acid, suggests that the operational definition is too broad. Because at least one putative heart H-FABP isoform, the mammary derived growth inhibitor, was an artifact (Specht et al. (1996) J. Biol. Chem. 271: 1943-49), the ensuing skepticism and confusion cast doubt on the existence of FABP isoforms in general. Yet, increasing data suggest that several FABPs, e.g. human intestinal I-FABP, bovine and mouse heart H-FABP, rabbit myelin P2 protein and bovine liver L-FABP may exist as true isoforms. In contrast, the rat liver L-FABP putative isoforms may actually be due either to bound ligand, post-translational S-thiolation and/or structural conformers. In any case, almost nothing is known regarding possible functions of either the true or putative isoforms in vitro or in vivo. The objective of this article is to critically evaluate which FABPs form biochemically defined or true isoforms versus FABPs that form additional forms, operationally defined as isoforms. In addition, recent developments in the molecular basis for FABP true isoform formation, the processes leading to additional operationally defined putative isoforms and insights into potential function(s) of this unusual aspect of FABP heterogeneity will be examined.
TL;DR: The identity, nature, function, and pathobiology of these fascinating newly discovered long-chain fatty acyl-CoA binding proteins are explored.
Abstract: The physiological role of long-chain fatty acyl-CoA is thought to be primarily in intermediary metabolism of fatty acids. However, recent data show that nM to μM levels of these lipophilic molecules are potent regulators of cell functionsin vitro. Although long-chain fatty acyl-CoA are present at several hundred μM concentration in the cell, very little long-chain fatty acyl-CoA actually exists as free or unbound molecules, but rather is bound with high affinity to membrane lipids and/or proteins. Recently, there is growing awareness that cytosol contains nonenzymatic proteins also capable of binding long-chain fatty acyl-CoA with high affinity. Although the identity of the cytosolic long-chain fatty acyl-CoA binding protein(s) has been the subject of some controversy, there is growing evidence that several diverse nonenzymatic cytosolic proteins will bind long-chain fatty acyl-CoA. Not only does acyl-CoA binding protein specifically bind medium and long-chain fatty acyl-CoA (LCFA-CoA), but ubiquitous proteins with multiple ligand specificities such as the fatty acid binding proteins and sterol carrier protein-2 also bind LCFA-CoA with high affinity. The potential of these acyl-CoA binding proteins to influence the level of free LCFA-CoA and thereby the amount of LCFA-CoA bound to regulatory sites in proteins and enzymes is only now being examined in detail. The purpose of this article is to explore the identity, nature, function, and pathobiology of these fascinating newly discovered long-chain fatty acyl-CoA binding proteins. The relative contributions of these three different protein families to LCFA-CoA utilization and/or regulation of cellular activities are the focus of new directions in this field.
TL;DR: Rat L-FABP isoforms differ markedly in both structure and ligand binding function, and displacement studies indicated that each isoform displayed distinct specificities for fatty acid/fatty acyl CoA chain length and unsaturation.
Abstract: Although native rat liver fatty acid binding protein (L-FABP) is composed of isoforms differing in isoelectric point, their comparative structure and function are unknown. These properties of apo- ...
TL;DR: Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
Abstract: Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins, a number of modified analytical procedures utilizing this reagent have been reported for the determination of proteins in serum, in antigen-antibody precipitates, and in insulin. Although the reagent would seem to be recommended by its great sensitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard to effects of variations in pH, time of reaction, and concentration of reactants, permissible levels of reagents commonly used in handling proteins, and interfering substances. Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
TL;DR: In this paper, the authors described a simplified version of the method and reported the results of a study of its application to different tissues, including the efficiency of the washing procedure in terms of the removal from tissue lipides of some non-lipide substances of special biochemical interest.
Abstract: Work from this laboratory resulted in the development of a method for the preparation and purification of brain lipides (1) which involved two successive operations. In the first step, the lipides were extracted by homogenizing the tissue with 2: 1 chloroform-methanol (v/v), and filtering the homogenate. In the second step, the filtrate, which contained the tissue lipides accompanied by non-lipide substances, was freed from these substances by being placed in contact with at least 5-fold its volume of water. This water washing entailed the loss of about 1 per cent of the brain lipides. This paper describes a simplified version of the method and reports the results of a study of its application to different tissues, including the efficiency of the washing procedure in terms of the removal from tissue lipides of some non-lipide substances of special biochemical interest. It also reports some pertinent ancillary findings. The modifications introduced into the method pertain only to the washing procedure. A chloroformmethanol extract of the tissue, prepared as described in the original version of the method, is mixed with 0.2 its volume of water to which, for certain purposes, different mineral salts may be added. A biphasic system without any interfacial fluff is obtained (2). The upper phase contains all of the non-lipide substances, most of the strandin, and only negligible amounts of the other lipides. The lower phase contains essentially all the tissue lipides other than strandin. In comparison with the original method, the present version has the advantage of being simpler, of being applicable to any scale desired, of substantially decreasing the losses of lipides incidental to the washing process, and, finally, of yielding a washed extract which can be taken to dryness without foaming and without splitting of the proteolipides (3).
TL;DR: Pulse-chase experiments in wild-type and mutant phage-infected cells provide evidence that the following particles called prohead I, II and III are successive precursors to the mature heads as discussed by the authors.
Abstract: Pulse-chase experiments in wild-type and mutant phage-infected cells provide evidence that the following particles called prohead I, II and III are successive precursors to the mature heads. The prohead I particles contain predominantly the precursor protein P23 and possibly P22 (mol. wt 31,000) and IP III (mol. wt 24,000) and have an s value of about 400 S. Concomitantly with the cleavage of most of P23 (mol. wt 55,000) to P23∗ (mol. wt 45,000), they are rapidly converted into prohead II particles which sediment with about 350 S. The prohead II particles contain, in addition to P23∗, the major constituents of the viral shella—a core consisting of proteins P22 and IP III. In cell lysates, prohead I and prohead II particles contain no DNA in a DNase-resistant form and are not bound to the replicative DNA. We cannot, however, positively rule out the possibility that these particles may have contained some DNA while in the cells. The prohead II particles are in turn converted into particles which sediment with about 550 S after DNase treatment (prohead III). During this conversion about 50% of normal DNA complement becomes packaged in a DNase-resistant form, and roughly 50% of the core proteins P22 and IP III are cleaved. In lysates the prohead III particles are attached to the replicative DNA. The prohead III particle appears to be the immediate precursor of the full mature head (1100 S). Cleavage of protein P22 to small polypeptides and conversion of IP III IP III∗ are completed at this time. No precursor proteins are found in the full heads. Studies with various mutant phage showed that the prohead II to III conversion is blocked by mutations in genes 16 and 17 and that the conversion of the prohead III particles to the mature heads is blocked by mutations in gene 49. Cleavage of the head proteins, however, occurs normally in these mutant-infected cells. We conclude that the cleavage of the major component of the viral shell, P23, into P23∗ precedes the DNA packaging event, whereas cleavage of the core proteins P22 and IP III appears to be intimately linked to the DNA packaging event. Models relating the cleavage processes to DNA encapsulation are discussed.
TL;DR: A protein of molecular weight ∼ 12,000 which binds long-chain fatty acids and certain other lipids has been identified in cytosol of intestinal mucosa, liver, myocardium, adipose tissue, and kidney and appears to be identical with the smaller of two previously described cytoplasmic anion-binding proteins.
Abstract: A protein of molecular weight approximately 12,000 which binds long-chain fatty acids and certain other lipids has been identified in cytosol of intestinal mucosa, liver, myocardium, adipose tissue, and kidney. Binding is noncovalent and is greater for unsaturated than for saturated and medium-chain fatty acids. This protein appears to be identical with the smaller of two previously described cytoplasmic anion-binding proteins. Binding of long-chain fatty acids by this protein is greater than that of other anions tested, including sulfobromophthalein, and does not depend on negative charge alone. The presence of this binding protein may explain previously observed differences in intestinal absorption among fatty acids, and the protein may participate in the utilization of long-chain fatty acids by many mammalian tissues.
TL;DR: Two hepatic cytoplasmic protein fractions, designated Y and Z, which bind sulfobromophthalein (BSP), bilirubin, and other organic anions, have been separated by G75 Sephadex gel filtration and appear to be important in the transfer of Organic anions from plasma into the liver.
Abstract: Two hepatic cytoplasmic protein fractions, designated Y and Z, which bind sulfobromophthalein (BSP), bilirubin, and other organic anions, have been separated by G75 Sephadex gel filtration. The physiologic role of these protein fractions has been investigated. They are present in the 110,000 g supernatant fraction from the livers of all the species tested (rats, mice, guinea pigs, Rhesus monkeys, sheep, and man). Tissues which do not preferentially extract BSP or bilirubin from plasma do not contain these fractions, with the exception of small intestinal mucosa which contains Z. Anion binding by Y and Z fractions is not due to contamination with albumin. These fractions are responsible for the cytoplasmic localization of bilirubin in Gunn rats, and the fractions bind bilirubin, BSP, or indocyanine green (ICG), whether given in vivo or added in vitro to liver supernate from normal rats. Flavaspidic acid-N-methylglucaminate, bunamiodyl, and iodipamide, drugs known to interfere with the hepatic uptake mechanism, compete with bilirubin and BSP for binding to Z. These proteins appear to be important in the transfer of organic anions from plasma into the liver and provide a tool for the investigation of hepatic uptake mechanisms.