Rat liver preproalbumin: in vitro synthesis and partial amino acid sequence

Albumin, an interesting and functionally diverse protein, varies from 'native' to 'effective' (Review)

Human serum albumins (HSAs) are synthesized in the liver and are the most abundant proteins in plasma of healthy human. They play an important role in the pathophysiological processes of the liver and even the whole organism. Previous studies have mainly focused on the regulation of HSAs' expression. However, with the progress of research in recent years, it has been found that the content of circulating albumin cannot fully reflect the biological function of albumin itself. Given the aforementioned fact, the concept of serum 'effective albumin concentration' has been proposed. It refers to the content of albumin that is structurally and functionally intact. Alterations in the molecular structure and function of albumin have been reported in a variety of diseases, including liver disease. Moreover, these changes have been verified to affect the progression of oxidative stress‑related diseases. However, the link between albumin structure and function has not been fully elaborated, and the mechanisms by which different forms of albumin affect disease also need to be further investigated. In this context, the present review mainly expounded the biological characteristics and functions of albumin, summarized the different types of post‑translational modification of albumin, and discussed their functional changes and possible mechanisms in non‑alcoholic fatty liver disease, alcoholic hepatitis, viral hepatitis and different stages of cirrhosis. This will help to improve understanding of the role of albumin in disease development and provide a more comprehensive physiological basis for it in disease treatment.

Long-term albumin treatment in patients with cirrhosis and ascites

Although proposed for the first time several decades ago, the possibility that long-term human albumin could be effective for the treatment of patients with cirrhosis and ascites has become a topic of scientific and clinical discussion in the last decade. Long-term albumin administration represents a completely different treatment perspective compared to acute or short-term uses of albumin. Results from the ANSWER and the MACHT studies indicate that long-term albumin treatment can be effective, safe and able to modify the course of the disease provided that albumin is given at a sufficient dose and for a sufficient time to restore physiological levels and functions of the circulating molecule, which are compromised, at least partially, in patients with decompensated cirrhosis. Further clinical studies and randomised trials are warranted to confirm the clinical benefits of long-term albumin therapy. Important areas for further research include determining the precise target population, the biomarkers of response, the optimal dose and frequency of albumin infusions, the stopping rules, and the cost-effectiveness of treatment in different healthcare systems across the world, particularly in those where the logistical issues and costs related to the periodic intravenous infusions may represent an important limitation to the implementation of this innovative approach in clinical practice. In this review, we will critically analyse the available data on long-term albumin treatment, focusing on the differences that exist between studies, the controversial issues and the future perspectives.

Role of albumin in the treatment of decompensated liver cirrhosis

PURPOSE OF REVIEW

Albumin has been used primarily as a plasma expander, since it leads to an increase in the circulating blood volume. Current generally recommended indications for albumin therapy in cirrhotic patients are the prevention of circulatory dysfunction after large-volume paracentesis, the prevention of hepatorenal syndrome (HRS) in patients with spontaneous bacterial peritonitis (SBP), and the management of HRS in combination with vasoconstrictors. Yet, new indications for albumin have been tested in the recent years and are outlined in this short review.

RECENT FINDINGS

New data show that albumin both supports the circulation and reduces systemic inflammation. In addition, to its oncotic function, it acts as an antioxidant, radical scavenger, and immune modulator. These nononcotic properties explain why long-term albumin administration in patients with decompensated cirrhosis may be useful in the prevention of associated complications (acute-on-chronic liver failure, infections). New data show that long-term albumin therapy in patients with cirrhosis and ascites improves survival, prevents complications, simplifies ascites management, and lowers hospitalization rates. The so-called disease-modifying effects of long-term albumin therapy may have a favorable effect on the course of the disease. Nevertheless, the optimal dosage and administration intervals have not yet been finally defined.

SUMMARY

Albumin therapy is effective in the indications already recommended by the guidelines. A possible extension of the indication for albumin administration in non-SBP infections and as long-term therapy is promising, but should be confirmed by further studies.

Albumin Substitution in Decompensated Liver Cirrhosis: Don't Forget Zinc

Decompensated liver cirrhosis has a dismal prognosis, with patients surviving on average for 2-4 years after the first diagnosis of ascites. Albumin is an important tool in the therapy of cirrhotic ascites. By virtue of its oncotic properties, it reduces the risk of cardiovascular dysfunction after paracentesis. Treatment with albumin also counteracts the development of hepatorenal syndrome and spontaneous bacterial peritonitis. More recently, the positive impact of long-term albumin supplementation in liver disease, based on its pleiotropic non-oncotic activities, has been recognized. These include transport of endo- and exogenous substances, anti-inflammatory, antioxidant and immunomodulatory activities, and stabilizing effects on the endothelium. Besides the growing recognition that effective albumin therapy requires adjustment of the plasma level to normal physiological values, the search for substances with adjuvant activities is becoming increasingly important. More than 75% of patients with decompensated liver cirrhosis do not only present with hypoalbuminemia but also with zinc deficiency. There is a close relationship between albumin and the essential trace element zinc. First and foremost, albumin is the main carrier of zinc in plasma, and is hence critical for systemic distribution of zinc. In this review, we discuss important functions of albumin in the context of metabolic, immunological, oxidative, transport, and distribution processes, alongside crucial functions and effects of zinc and their mutual dependencies. In particular, we focus on the major role of chronic inflammatory processes in pathogenesis and progression of liver cirrhosis and how albumin therapy and zinc supplementation may affect these processes.

Optimal Management of Cirrhotic Ascites: A Review for Internal Medicine Physicians

Clinical history of liver cirrhosis is characterised by two phases: the asymptomatic phase, also termed 'compensated cirrhosis', and the phase of complications due to the development of portal hypertension and liver dysfunction, also termed 'decompensated cirrhosis', in which patients may develop ascites, the most frequent and clinically relevant complication of liver cirrhosis. Ascites can be classified into uncomplicated and complicated according to the development of refractoriness, spontaneous bacterial peritonitis (SBP) or the association with hepatorenal syndrome (HRS). In this narrative review, we will extensively discuss the optimal pharmacological and non-pharmacological management of cirrhotic ascites with the aim to offer an updated practical guide to Internal Medicine physicians. According to the amount of fluid in the abdominal cavity, uncomplicated ascites is graded from 1 to 3, and the cornerstone of its management consists of restriction of salt intake, diuretics and large-volume paracentesis (LVP); in recent years, long-term administration of human albumin has acquired a new interesting role. Refractory ascites is primarily managed with LVP and transjugular intrahepatic portosystemic shunt (TIPS) placement in selected patients. The occurrence of renal impairment, especially HRS, worsens the prognosis of patients with cirrhotic ascites and deserves a specific treatment. Also, the management of SBP faces the rising and alarming spread of antibiotic resistance. Hepatic hydrothorax may even complicate the course of the disease and its management is a challenge. Last but not least, liver transplantation (LT) is the ultimate and more effective measure to offer to patients with cirrhotic ascites, particularly when complications occur.

Albumin in decompensated cirrhosis: new concepts and perspectives

The pathophysiological background of decompensated cirrhosis is characterised by a systemic proinflammatory and pro-oxidant milieu that plays a major role in the development of multiorgan dysfunction. Such abnormality is mainly due to the systemic spread of bacteria and/or bacterial products from the gut and danger-associated molecular patterns from the diseased liver triggering the release of proinflammatory mediators by activating immune cells. The exacerbation of these processes underlies the development of acute-on-chronic liver failure. A further mechanism promoting multiorgan dysfunction and failure likely consists with a mitochondrial oxidative phosphorylation dysfunction responsible for systemic cellular energy crisis. The systemic proinflammatory and pro-oxidant state of patients with decompensated cirrhosis is also responsible for structural and functional changes in the albumin molecule, which spoil its pleiotropic non-oncotic properties such as antioxidant, scavenging, immune-modulating and endothelium protective functions. The knowledge of these abnormalities provides novel targets for mechanistic treatments. In this respect, the oncotic and non-oncotic properties of albumin make it a potential multitarget agent. This would expand the well-established indications to the use of albumin in decompensated cirrhosis, which mainly aim at improving effective volaemia or preventing its deterioration. Evidence has been recently provided that long-term albumin administration to patients with cirrhosis and ascites improves survival, prevents complications, eases the management of ascites and reduces hospitalisations. However, variant results indicate that further investigations are needed, aiming at confirming the beneficial effects of albumin, clarifying its optimal dosage and administration schedule and identify patients who would benefit most from long-term albumin administration.

Structural investigations of stereoselective profen binding by equine and leporine serum albumins

Serum albumin, the most abundant transport protein of mammalian blood, interacts with various nonsteroidal anti-inflammatory drugs (NSAIDs) affecting their disposition, metabolism, and excretion. A big group of chiral NSAIDs transported by albumin, profens, is created by derivatives of 2-arylpropionic acid. The chiral center in the structures of profens is adjacent to the carboxylate moiety and often determines different pharmacological properties of profen enantiomers. This study describes crystal structures of two albumins, isolated from equine and leporine serum, in complexes with three profens: ibuprofen, ketoprofen, and suprofen. Based on three-dimensional structures, the stereoselectivity of albumin is discussed and referred to the previously published albumin complexes with drugs. Drug Site 2 (DS2) of albumin, the bulky hydrophobic pocket of subdomain IIIA with a patch of polar residues, preferentially binds (S)-enantiomers of all investigated profens. Almost identical binding mode of all these drugs clearly indicates the stereoselectivity of DS2 towards (S)-profens in different albumin species. Also, the affinity studies show that DS2 is the major site that presents high affinity towards investigated drugs. Additionally, crystallographic data reveal the secondary binding sites of ketoprofen in leporine serum albumin and ibuprofen in equine serum albumin, both overlapping with previously identified naproxen binding sites: the cleft formed between subdomains IIIA and IIIB close to the fatty acid binding site 5 and the niche created between subdomains IIA and IIIA, called fatty acid site 6.

Targeted expression of human serum albumin to potato tubers

Complementary DNA expression of mature human serum albumin was engineered into potato plants under the transcriptional control of patatin B33 promoter and potato proteinase inhibitor II terminator. Protein secretion was achieved by using the signal sequence from potato proteinase inhibitor II. Recombinant albumin accumulated up to 0.2% of total soluble tuber protein in single transformant lines, regardless of the potato cultivar used. Electrophoretic mobility and N-terminal amino acid sequence analysis of partially purified recombinant albumin confirmed proper processing of an immune responsive recombinant albumin, and revealed that the proteinase inhibitor II signal sequence was correctly removed. No further optimisation of these yields was obtained by HSA expression in patatin antisense plants (line Pas58). Subcellular localisation showed that recombinant protein was successfully targeted to the apoplast. Potato tubers may be used, by applying this technology, to produce other heterologous proteins of interest in the biopharmaceutical industry.

Albumin metabolism in the nephrotic syndrome: the effect of dietary protein intake

The nephrotic syndrome is characterized by increased urinary excretion of albumin and other serum proteins, accompanied by hypoproteinemia and edema formation. Nephrotic patients have lower serum albumin concentrations than do patients undergoing continuous ambulatory peritoneal dialysis when albumin and protein losses are the same in both groups, suggesting that nephrotic patients may not maximally adapt to loss of protein. The fractional rate of albumin catabolism is increased in nephrotic patients, possibly as a result of increased albumin catabolism by the kidney, but the absolute albumin catabolic rate is decreased in nephrotic patients. The rate of albumin synthesis may be increased, but not sufficiently to maintain normal serum albumin concentration or albumin pools. Augmentation of dietary protein in nephrotic rats directly stimulates albumin synthesis by increasing albumin mRNA content in the liver, but also causes an increase in glomerular permeability to macromolecules so that much if not all of the excess albumin synthesized is lost in the urine. When dietary protein is restricted, the rate of albumin synthesis is not increased either in nephrotic patients or in rats, despite severe hypoalbuminemia. Although dietary protein supplementation may lead to positive nitrogen balance, dietary protein supplementation alone does not cause an increase in serum albumin concentration or body albumin pools, and may instead cause further albumin pool depletion because of changes induced in glomerular permselectivity. The use of angiotensin-converting enzyme inhibitors may blunt the increased albuminuria caused by dietary protein supplementation and allow albumin stores to be increased.

Increased proportion of proapolipoprotein A-I in HDL from patients with liver cirrhosis and hepatitis

We examined the isoform pattern of apolipoprotein A-I (apo A-I) in high density lipoprotein from patients with liver disease. An increase in the proportion of proapo A-I was evident in patients with decompensated liver cirrhosis, acute hepatitis and hepatocellular carcinoma. The rate of conversion from proapo A-I to apo A-I was low in sera from those with liver disease, compared to normal controls. The proportion of proapo A-I showed a tendency toward increase with advance in liver damage. These results suggest that the liver is participating in the reaction converting proapo A-I to the mature apo A-I.

N-terminal sequence homologies in interstitial retinol-binding proteins from 10 vertebrate species

We report here the first comprehensive comparative NH2-terminal sequence studies of interstitial retinol-binding protein (IRBPs) from nine mammals (including cattle) and one amphibian. This study has revealed that in many species the N-terminus of IRBP includes a 3-6 amino acid extension. IRBP possessing this leader sequence is sometimes mixed with IRBP from which this sequence has been excised.

Isolation and nucleotide sequence of a cDNA clone encoding rat mitochondrial malate dehydrogenase

We have determined the complete sequence of the rat mitochondrial malate dehydrogenase (mMDH) precursor derived from nucleotide sequence of the cDNA. A single synthetic oligodeoxynucleotide probe was used to screen a rat atrial cDNA library constructed in lambda gt10. A 1.2 kb full-length cDNA clone provided the first complete amino acid sequence of pre-mMDH. The 1014 nucleotide-long open reading frame encodes the 314 residue long mature mMDH protein and a 24 amino acid NH2-terminal extension which directs mitochondrial import and is cleaved from the precursor after import to generate mature mMDH. The amino acid composition of the transit peptide is polar and basic. The pre-mMDH transit peptide shows marked homology with those of two other enzymes targeted to the rat mitochondrial matrix.

Acyl-Coa oxidase and hydratase-dehydrogenase, two enzymes of the peroxisomal beta-oxidation system, are synthesized on free polysomes of clofibrate-treated rat liver

We investigated the site of synthesis of two abundant proteins in clofibrate-induced rat hepatic peroxisomes. RNA was extracted from free and membrane-bound polysomes, heated to improve translational efficiency, and translated in the mRNA-dependent, reticulocyte-lysate-cell-free, protein-synthesizing system. The peroxisomal acyl-CoA oxidase and enoyl-CoA hydratase-beta-hydroxyacyl-CoA dehydrogenase 35S-translation products were isolated immunochemically, analyzed by SDS PAGE and fluorography, and quantitated by densitometric scanning. The RNAs coding for these two peroxisomal proteins were found predominantly on free polysomes, and the translation products co-migrated with the mature proteins. As in normal rat liver, preproalbumin and catalase were synthesized mainly by membrane-bound and by free polysomes, respectively. mRNAs for a number of minor 35S-translation products also retained by the anti-peroxisomal immunoadsorbent were similarly found on free polysomes. These results, together with previous data, allow the generalization that the content proteins of rat liver peroxisomes are synthesized on free polysomes, and the data imply a posttranslational packaging mechanism for these major content proteins.

Heating RNA before cell-free translation is essential for the efficient and reproducible synthesis of several peroxisomal proteins

Total RNA, extracted with guanidinium thiocyanate from liver of clofibrate-treated rats, was translated in vitro. Heating the RNA at 60 degrees C for 5 min before translation increased the synthesis of three peroxisomal polypeptides 10-100-fold. Preproalbumin synthesis increased 10-fold. Total incorporation of [35S]methionine into proteins merely doubled. Heating is essential for reproducible and adequate translation of mRNAs coding for peroxisomal and some other proteins.

Isolation and characterization of xenopus laevis albumin mRNA

The messenger RNA for albumin was isolated from the liver of male frogs. Purification was achieved using oligo(dT)-cellulose chromatography and sucrose gradient centrifugation under denaturing conditions. As judged by translational activity in a cell-free protein-synthesizing system derived from rabbit reticulocytes, albumin mRNA was enriched 259-fold as compared to the total ribonucleic acid of the liver cells. Purified albumin mRNA migrated after sucrose gradient centrifugation as a single symmetrical peak of approximately 17 S and also moved as a single band following denaturing agarose gel electrophoresis. Albumin mRNA possess properties compatible with the presence of a poly(adenylic acid) sequence. Translation in vitro yielded a product which is immunoprecipitable with anti-(frog albumin) and which showed a single radioactive peak having a molecular weight of about 74000 in sodium dodecylsulfate/polyacrylamide gel electrophoresis. Complementary DNA was synthesized using reverse transcriptase, and, as a template, purified albumin mRNA. Following hybridization under conditions of excess RNA, the rot1/2 of albumin mRNA was found to be 1.8 X 10-3 mol . s . 1-1. This result also confirmed that albumin nRNA had been isolated in a highly purified form.

Absence of albumin mRNA in the liver of analbuminemic rats

Albumin synthesis in the liver of analbuminemic rats, established as a strain from a stock of Sprague-Dawley rats, was examined in vivo by labeling protein by intraperitoneal injection of L-[3H]leucine. Albumin was not synthesized in the liver of analbuminemic rats, whereas its synthesis amounted to about 14% of the total protein synthesis in the liver of normal rats. The RNA content and size distribution of the total polysomes in the liver of analbuminemic rats were not significantly different from those of normal rats. However, no functional mRNA coding for albumin was found in poly(A)-containing RNA from the liver of analbuminemic rats when tested with a cell-free translation system derived from rabbit reticulocytes. Moreover, the amount of the RNA sequence that could hybridize to purified albumin cDNA was more than 750 times greater in the liver of normal rats than in that of analbuminemic rats.

Synthesis of rat liver microsomal cytochrome b5 by free ribosomes

Free and membrane-bound polyribosomes were separated from liver homogenates and characterized by electron microscopy. Using the wheat germ cell-free translation system, total translation products of poly A+RNA extracted from free polyribosomes (poly A+RNAf) showed some correlation to total liver cytosol proteins. In contrast, translation products of poly A+RNA from membrane-bound polyribosomes (poly A+RNAmb) showed some similarity to rat serum. Antibody to purified rat serum albumin immunoprecipitated from only the translation products of poly A+RNAmb a single polypeptide of mol wt 68,000. i.e., 3,000 greater than secreted serum albumin. In contrast, antibody to detergent-extracted cytochrome b5 immunoprecipitated from only the translation products of poly A+RNAf a single polypeptide of mol wt 17,500, identical to that of microsomal cytochrome b5. A consideration of the known properties of cytochrome b5 is consistent with an exclusive site of synthesis on free ribosomes.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

In vitro synthesis of a putative precursor of mitochondrial ornithine transcarbamoylase

Ornithine transcarbamoylase (OTCase; ornithine carbamoyltransferase; carbamoyl phosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3), a major mitochondrial matrix enzyme in ureotelic animals, is synthesized on cytoplasmic ribosomes and translocated across both mitochondrial membranes to the matrix. In an attempt to identify the primary translation product (or an early intermediate) that is the substrate for this transport process, we translated rat liver polysomal RNA in vitro by using the rabbit reticulocyte lysate system. Immunoprecipitation of the [35S]methionine-labeled translation mixture was performed by using monospecific OTCase antiserum and the immunoadsorbent Staphylococcus aureus. Approximately 0.3% of total trichloroacetic acid-insoluble 35S-labeled material was specifically precipitated. Analysis of the precipitate by fluorography of a dried sodium dodecyl sulfate/polyacrylamide gel showed a single major translation product whose mobility corresponded to a polypeptide of 43,000 daltons, a value approximately 4000 daltons greater than that noted for the "mature" OTCase subunit isolated from rat liver. This translation product was not precipitated by preimmune rabbit serum, and excess unlabeled mature OTCase competed with it for interaction with OTCase antiserum. These results suggested that rat liver OTCase, like a number of other cytoplasmically synthesized organellar proteins, is initially made as a larger precursor that contains an amino acid sequence necessary to confer on OTCase its transport properties. The potential application of these findings to the study of inherited complete OTCase deficiency in humans is discussed.

Studies on the intracellular segregation of polyribosome-associated messenger ribonucleic acid species in the lactating guinea-pig mammary gland

1. Free and membrane-bound polyribosomes were isolated and the associated mRNA species characterized by cell-free protein synthesis, RNA-complexity analysis and polyribosome run-off in vitro. 2. Of the recovered polyribosomal RNA 85% was associated with membrane-bound polyribosomes and contained 87--93% of the total milk-protein mRNA species as assessed by cell-free protein synthesis or RNA-complexity analysis. 3. RNA-complexity analysis showed that the abundant (milk-protein mRNA assumed) species constituted 55% of the post-nuclear poly(A)-containing RNA population, the remainder consisting of a moderately abundant population (18%) and a low abundance population (27%). Calculations suggest that each population contained up to 2, 48 and 5000 different species respectively. 4. RNA-complexity analysis of the free polyribosomal poly(A)-containing RNA demonstrated that all the species in the post-nuclear fraction were present, though in different proportions, the abundant, moderately abundant and low-abundance groups representing 38, 30 and 32% of this population. 5. RNA-complexity analysis of the membrane-bound polyribosomal poly(A)-containing RNA revealed a more limited population, 72% consisting of the abundant (milk-protein mRNA) species, and 28% a population of up to 900 RNA species. 6. Polyribosome run-off confirmed that milk-protein mRNA was associated with the membrane-bound and free polyribosomes, but represented only a small fraction of the total protein synthesized by the latter. 7. Comparative analysis of milk proteins synthesized in mRNA-directed cell-free systems, or by run-off of free and of membrane-bound polyribosomes, is consistent with the interpretation that in vivo the initiation of protein synthesis occurs on free polyribosomes, followed by the attachment of a limited population to the endoplasmic reticulum. After attachment, but before completion of peptide synthesis, the detachable N-terminal peptide sequence of one of these(pre-alpha-lactalbumin) is removed. 8. The results are discussed in terms of the mechanisms involved in the intracellular segregation of mRNA species in the lactating guinea-pig mammary gland.

Synthesis and assembly of membrane glycoproteins: presence of leader peptide in nonglycosylated precursor of membrane glycoprotein of vesicular stomatitis virus

Translation of mRNA encoding vesicular stomatitis virus envelope glycoprotein G by as membrane-free ribosomal extract obtained from HeLa cells yielded a nonglycosylated protein (G1 (Mr 63,000). In the presence of added microsomal membranes, G1 was converted to the glycosylated protein (G2 (Mr 67,000) which is inserted in the membrane vesicles as a transmembrane protein. Labeling with methionine donated by wheat germ initiator tRNA1Met showed that G1 but not G2 contains methionine in the NH2-terminal position. Determination of the NH2-terminal sequence of G1, G2, and G showed that a leader peptide of 16 amino acids is present in G1 but absent from the glycosylated proteins G2 and G. This leader peptide contains at least 62% hydrophobic amino acids and is removed presumably during insertion of G1 into the membrane.

Processing in vitro of precursor periplasmic proteins from Escherichia coli

Precursors of two secreted periplasmic proteins in Escherichia coli, arabinose-binding protein and maltose-binding protein, were synthesized in vitro on membrane-bound polysomes. Addition of Triton X-100 to the system resulted in processing of the precursors to mature forms.

Synthesis of catalase in two cell-free protein-synthesizing systems and in rat liver

Rat liver polysomal RNA was translated in the rabbit reticulocyte lysate and in the wheat germ cell-free protein-synthesizing systems, using [(35)S]methionine as label. The catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase, EC 1.11.1.6) that was synthesized was isolated by immunoprecipitation and characterized by electrophoresis in sodium dodecyl sulfate/polyacrylamide gels followed by fluorography. The catalase made in both systems migrated more slowly during electrophoresis than did purified peroxisomal catalase. By comparison with standards of known molecular mass, the cell-free products were estimated to be about 4000 daltons larger than the purified enzyme. We also investigated the biosynthesis of catalase in vivo by injecting [(35)S]methionine into rats. The precursor of catalase known to be synthesized in liver and found in the high-speed supernatant 8 min later [Lazarow, P. B. & de Duve, C. (1973) J. Cell Biol. 59, 491-506] was isolated immunochemically. For comparison, 1-day-old completed catalase was immunoprecipitated from peroxisomes. The migrations in sodium dodecyl sulfate gels of the 8-min-old precursor and the subunit of the day-old enzyme were indistinguishable and approximately the same as the migration of the cell-free products. These results indicate that catalase's apparent size does not change when it enters peroxisomes but rather decreases during the chemical purification procedure.

Position of the extra amino acid sequence in the precursor arabinose-binding protein of Escherichia coli

The extra amino acid sequence in the precursor arabinose-binding protein was shown to be either close to or at the N-terminus.

Cycloheximide causes increased accumulation of translatable mRNA for tyrosine aminotransferase and tryptophan oxygenase in livers of cortisol-treated rats

Messenger RNA activities for two cortisol-inducible enzymes, tyrosine aminotransferase and tryptophan oxygenase, have been determined by translation in a wheat germ system. The effects of cycloheximide on the two mRNA activities have been evaluated. Cortisol leads to an increase of the translatable mRNAs for tyrosine aminotransferase and tryptophan oxygenase with a maximum at approximately 6 h. Cycloheximide was administered 4 h after treatment with cortisol; 2 h later, the activities of tyrosine aminotransferase and tryptophan oxygenase mRNA had increased five-fold and two-fold, respectively, compared to the activities reached with cortisol alone. Thereafter the amount of the two translatable mRNAs declined, though 14 h after cortisol administration the mRNA activities were still several fold higher than in control animals. Application of alpha-amanitin together with cycloheximide did not prevent an increased accumulation of specific translatable mRNAs. The increase in tyrosine aminotransferase and tryptophan oxygenase activity by cortisol was immediately blocked by cycloheximide. Whereas tryptophan oxygenase activity rapidly declined after cycloheximide application, tyrosine aminotransferase activity remained at the same level. Approximately 4 h thereafter, both enzyme activities increased again.