Types Of Polypeptide Chains Research Articles

Removal of N-terminal methionine of human interferon α-2b by co‐producing with Pyrococcus furiosus methionine aminopeptidase in Escherichia coli

In our previous studies, expression of human interferon α-2b gene in Escherichia coli gave three types of polypeptide chains in nearly equimolar ratio. They include molecules with N-terminal methionine, molecules without N-terminal methionine, and molecules with acetylated N-terminal. This heterogeneity is not required in therapeutic applications. In order to improve the removal rate of N-terminus methionine, co-expression of human interferon α-2b and methionine aminopeptidase genes was performed in E. coli. The co-expression resulted in production of human interferon α-2b with dominance of molecules without N-terminal methionine and very few of them were acetylated at the N-terminus. Our findings contribute significantly to efforts for the production of homogenous therapeutic proteins which represent the exact recombinant replica of their native proteins.

Barriers Hindering Maternal Care of Children Suffering from Thalassemia: An Assessment Study

Background: Thalassemia is a group of genetic disorders of blood, characterized by decreased synthesis of one or two types of polypeptide chain (α or β) that form abnormal human hemoglobin molecules. Aim of this study: was to assess barriers hindering maternal care of their children suffering from thalassemia. Research design: A descriptive design was utilized in carry out this study. Setting: The study was conducted in Pediatric Hematology Outpatient Clinic at both Ain Shams University and Zagazig University Hospitals. Subject: A Purposive sample composed of 100 mothers (50 from each study setting) provided care to their children suffering from thalassemia. Tools of data collection: An interviewing questionnaire sheet that was designed by the researcher to assess barriers hindering maternal care of their children suffering from thalassemia. Results: Most of the studied mothers were having physical, psychological, nutritional, educational barriers and sleep disorders that hinder care of their children suffering from thalassemia. Conclusion: There are barriers that prevent the mothers from provide care of children with thalassemia and considers physical barriers as the main barriers are meeting the mothers when care her child with thalassemia. Recommendations: Periodic assessment of maternal practices in care of their thalassemic children and Identify barriers hindering maternal care.

Development of a stable eukaryotic strain producing fully human monoclonal antibody on the basis of the human antibody against ectromelia virus

Fully­human antibodies have a great therapeutic importance; however, the development of stable strains providing a high level of production of full­size antibodies is a challenging task, as antibody molecules contain two types of polypeptide chains. To develop the producing strain, random integration of the plasmid containing the gene encoding the target protein into the genome of the host cells is commonly used. The aim of this study was the development of an original expression system, using gene targeting to integrate the gene encoding the fully­human antibody into the transcriptionally active region of the genome of eukaryotic suspension cells CHO­S. To develop a stable strain, the cassette vector plasmid pCDNA5/FRTDHFR­CH­CL containing the site of homologous recombination and the genes encoding heavy and light chains of the fully human antibody of the IgG1/kappa class was constructed at the first step. Notably, DNA of the plasmid pCDNA5/FRT­DHFR­CH­CL was organized in such a way that the restriction sites for rapid cloning of DNA fragments encoding the variable domains of heavy and light chains were inserted upstream of the sequences encoding constant domains of the heavy and light chains of the antibody. Secondly, DNA fragments encoding the variable domains of the heavy and light chains of antibody against orthopoxvirus protein p35 were inserted into the pCDNA5/FRT­DHFRCH­CL cassette plasmid. Then, CHO­S/FRT cells, which contain the FRT­site for homologous recombination and are able to produce green fluorescence protein GFP, were transfected with the constructed plasmid. After the insertion of the target genes into the FRT­site, GFP production was supposed to stop. Using this selection system, a stable clone producing target antibody fh8E was selected with the level of production of about 100 μg/ml. The binding affinity of purified antibody fh8E with the targeted protein, measured by surface plasmon resonance, was 12 nM. In addition, antibody fh8E demonstrated anti­vaccinia virus activity in the plaque reduction neutralization test in vitro.

Pattern of Growth Retardation and Sexual Maturation in Children having Beta Thalassaemia

Introduction: Thalassaemia is a group of genetic disorders of blood, characterized by decreased synthesis of one of two types of poly peptide chain (α or ß) that form a normal adult human haemoglobin molecule (Hb A- α2 ß2). This results in decreased filling of red cell with haemoglobin and anaemia. Retardation of growth and delayed sexual maturation can occur as a complication of thalassaemia. The objectives of this study were to study the pattern of growth failure and sexual maturity rate (SMR) in children with β-thalassaemia major, and to compare it with controls.Material and Methods: In this case-control study conducted simultaneously at two centres at Bebe Nanki Mother And Child Care Centre, Amritsar and Sri Guru Ram Das Charitable hospital, Amritsar, the growth parameters (height,weight and sexual maturation ) and serum ferritin levels of a total of 114 patients aged 8-16 years (64 males and 50 females) with β-thalassaemia major were compared with those of 100 healthy controls of the same age and gender.Results: Underweight was observed in 89(78.1%) of patient group and 9(9%) of control group. Short stature was observed in 64(56.1%) patients and 7(7%) of the control group. The mean age of menarche for female thalassaemia patients was 12.11±2.1 years and for control females was 11.42±1.11years, The SMR were delayed in 108(95%) of patients and in 6 (6%) of controls. The level of serum ferritin was found to be significantly associated with delayed SMR in thalassaemia patients.Conclusion: Growth failure and delayed SMR significantly occur in thalassaemia patients, when compared to the controls. Adequate chelation therapy can help in controlling serum ferritin levels and thereby facilitating normal physical growth and sexual development in chronically transfused thalassaemia patients.J Nepal Paediatr Soc 2016;36(1):56-60

ABSTRACT 676

Background and aims: Hemophagocytic Lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation. HLH and sepsis-induced multiple organ failure share similar clinical features and biomarkers. The correct diagnosis is essential for strategizing the management including immune modulation. Ferritin is one of the 8 diagnostic criteria for HLH. Ferritin is made up of 2 types of polypeptide chains, heavy and light. Synthesis of heavy chain ferritin, specifically, is induced by tumor necrosis factor-alpha via the NF-KB pathway. Currently, there is no study on these ferritin subtypes in HLH and sepsis. Aims: The aim of this study is to describe the heavy and light chain ferritins in HLH and septic patients. Methods: Plasma samples of pediatric patients with severe sepsis were collected from a single center, and with HLH from a collaborative multicenter HLH study group. We analyzed light and heavy chain ferritins by using Western blotting, monoclonal antibodies, and radio optical densitometry. Results: We analyzed plasma from 11 severe sepsis and 8 HLH patients. We found the presence of light chain ferritin in the plasma of 2 severe sepsis and 4 HLH patients. We found the presence of heavy chain ferritin in the plasma of all severe sepsis and HLH patients. The concentration of heavy chain ferritin was 3.6 times more in HLH patients compared to severe sepsis patients. Conclusions: Heavy chain ferritin is present in both HLH and severe sepsis patients. Heavy chain ferritin seems to be more elevated in patients with HLH compared to severe sepsis. More studies are warranted.

Effectiveness of an educational health programme on mothers’ knowledge and practices of thalassaemic children receive desferal therapy in Hawler thalassemia center/Erbil City

Background and objective: Thalassaemia is a heredity blood diseases characterised by decreased synthesis of one of the two types of polypeptide chains (β or α) which form the normal adult human hemoglobin molecule (HbA, α2‚β2), resulting in decreased filling of the red cells with haemoglobin, and cause anaemia. The study aimed to improve mothers’ knowledge and practices of Thalassaemic children who are using Desferal therapy. Methods: A quasi-experimental study was carried out at Hawler Thalassemia Center in Erbil City from the 1st of March to the end of May 2010. One hundred mothers were selected and divided into two groups, 50 mothers exposed to the educational programme (study group) and a second group of (50) mothers were served as control. Pre and post test of subject of interest were done during the two occasions. Results: The results revealed that mothers’ knowledge and practices in the study group were improved. There is no significant association between mothers’ knowledge and practices with socio-demographic characteristics at pre-test which became significant at post-test . Conclusion: Yet, most of the mothers in the study group have gained benefit from implementation of this educational programme.

Comparison of the three-dimensional structures of recombinant human H and horse L ferritins at high resolution

Mammalian ferritins are 24-mers assembled from two types of polypeptide chain which provide the molecule with different functions. H(eavy) chains catalyse the first step in iron storage, the oxidation of iron(II). L(ight) chains promote the nucleation of the mineral ferrihydrite enabling storage of iron(III) inside the protein shell. We report here the comparison of the three-dimensional structures of recombinant human H chain (HuHF) and horse L chain (HoLF) ferritin homopolymers, which have been refined at 1.9 Å resolution. There is 53% sequence identity between these molecules, and the two structures are very similar, the H and L subunit α-carbons superposing to within 0.5 Å rms deviation with 41 water molecules in common. Nevertheless, there are significant important differences which can be related to differences in function. In particular, the centres of the four-helix bundles contain distinctive groups of hydrophilic residues which have been associated with ferroxidase activity in H chains and enhanced stability in L chains. L chains contain a group of glutamates associated with mineralisation within the iron storage cavity of the protein.

Interferon gamma signals via a high-affinity multisubunit receptor complex that contains two types of polypeptide chain.

Signaling by interferon gamma (IFN-gamma) requires two structurally related cell surface proteins: a ligand-binding polypeptide, known as the IFN-gamma receptor (IFN-gamma R), and an accessory factor. However, it is not known whether IFN-gamma forms a ternary complex with the IFN-gamma R and accessory factor to initiate signaling. Here we demonstrate complex formation between IFN-gamma and the two proteins, both in solution and at the cell surface. We observe complexes containing ligand, two molecules of IFN-gamma R (designated the IFN-gamma R alpha chain), and one or two molecules of accessory factor (designated the IFN-gamma R beta chain). Transfected cells expressing both IFN-gamma R chains bind IFN-gamma with higher affinity than do cells expressing alpha chain alone. Anti-beta-chain antibodies prevent the beta chain from participating in the ligand-receptor complex, reduce the affinity for IFN-gamma, and block signaling. Soluble alpha- or beta-chain extracellular domains also inhibit function. These results demonstrate that IFN-gamma signals via a high-affinity multisubunit complex that contains two types of receptor chain and suggest a potential approach to inhibiting specific actions of IFN-gamma by blocking the association of receptor subunits.

Multiple isoforms of the human pentraxin serum amyloid P component.

Human serum amyloid P component (SAP) isolated from 20 healthy individuals was analyzed by anion exchange chromatography and isoelectric focusing (IEF) in order to investigate the existence of multiple forms of SAP and interindividual structural differences. Anion exchange chromatography showed one major and several minor subpopulations of SAP. IEF of all SAP isolates showed a previously unreported degree of heterogeneity with six isoelectric forms (pKi range 5.5-6.1) and with minor interindividual differences in respect of isoelectric points. Total enzymatic deglycosylation of SAP reduced the number of bands in IEF to two indicating the existence of two types of polypeptide chains.

Two-dimensional electrophoresis of Arenicola marina extracellular hemoglobin: Separation of chains with identical molecular mass but different isoelectric point

1. 1. On the basis of their molecular masses, four types of polypeptides (A, B, C, D) were obtained by SDS-PAGE of the extracellular hemoglobin of the polychaete annelid Arenicola marina. 2. 2. On 2-dimensional polyacrylamide gel electrophoresis, the erythrocruorin dissociated into six different types of polypeptide chains; A 1, A 2, B 1, B 2, C and D. 3. 3. A 1 and B 1 migrate in 2-dimensional electrophoresis at the same position as α and β chains of human hemoglobin.

Biochemical and genetic analysis of a maltopentaose‐producing amylase from an alkaliphilic Gram‐positive bacterium

Two amylases have been purified from the culture fluid of an alkaliphilic bacterium. Amylase A-60 consists of a single type of polypeptide chain of 60 kDa and exhibits an alpha-amylase-type of starch cleavage. Amylase A-180 is approximately 180 kDa in size, represents the largest exoenzyme so far identified in prokaryotes and in the initial enzyme reaction cleaves starch exclusively to maltopentaose. A-60 and A-180 are immunologically unrelated enzymes. The structural gene for amylase A-180 has been cloned and its nucleotide sequence was determined. An open reading frame was identified for a putative protein of 182 kDa whose amino-terminal sequence, deduced from the nucleotide sequence, was identical in 23 out of 25 positions to that determined for the protein. The amino-terminus of the mature protein, at the gene level, is preceded by a sequence segment showing all the characteristics of a signal peptide from Gram-positive bacteria. Analysis of the deduced amino acid sequence revealed that the 70-kDa N-terminal part is similar to classical alpha-amylases. The C-terminal part contains three repeated sequence blocks of 99 amino acid residues each which are also present in two bacterial beta-amylases. It appears, therefore, that A-180 has arisen by gene fusion events.

Evolution of variable and constant domains and joining segments of rearranging immunoglobulins

The rearranging immunoglobulins (Igs) are a family of recognition and defense proteins found in all vertebrate classes. These proteins consist of two types of polypeptide chains; each of these contains a variable (V) domain, a joining (J) segment, and a constant (C) region, which can itself consist of one to four domains. The distinction between light and heavy chains is an ancient one phylogenetically that is reflected in the structures of V, J, and C regions. Despite the early emergence of these genetic elements, conservatism is apparent in the peptide structures encoded by V, J, and C exons. C regions of heavy chains did not evolve as single units; rather the individual domains show their own clustering patterns, which apparently are independent of heavy-chain designation or species. C-region domains of light chains and the T cell receptor beta chain are similar to one another and to the most carboxyl-terminal domain of heavy chains. Comparison of the light chains of sharks, bullfrogs, chickens, and mammals indicated that a phylogenetic distinction can be made between kappa and lambda light chains. V and J segments of the rearranging T cell receptors alpha, gamma, and delta are homologous to the corresponding segments of Igs, but their C regions form a group that is markedly distinct from those of conventional Igs and Tcr beta.

A monoclonal antigen-binding T cell immunoprotein: Antigenic relatedness to T cell receptor β chain FR1 V and J peptide segments: Physicochemical distinctiveness from classical immunoglobulins and T cell receptor heterodimers

The monoclonal murine T cell hybridoma, 51H7D, was previously shown to bind the arsazobenzene hapten and to produce a soluble antigen-binding molecule. In this paper we characterize this antigen-binding immunoprotein for its relationship to known T cell receptors serologically, using antibodies specific for variable region framework, or joining region peptides predicted from gene sequence and by biochemical means. The 51H7D cell expresses a protein with subunit size of approximately 31,000, that reacts antigenically with affinity-purified antibodies directed against synthetic first framework and joining segment peptides, corresponding to the gene sequence of the T cell receptor β chain, YT35. This molecule does not react with affinity-purified antibodies directed against murine immunoglobulin, framework 1 sequences of α and γ T cell receptors, or with antibodies against synthetic heavy chain joining segments. The subunit of mol. wt 31,000 can form higher aggregates, notably in the mol. wt range of 60,000–70,000, depending upon extraction conditions. The soluble form of the antigen-binding molecule bears the Jβ cross-reactive determinant and occurs predominantly as a charge restricted molecular species of approximate mol. wt 60,000–70,000. The purified molecule has a blocked N-terminus, but quantitative statistical analysis of its amino acid composition indicates a closer relatedness to T cell receptor β chains and other antigen-binding T cell products, than it has to α, γ or δ TCR chains. No evidence for more than one type of polypeptide chain was found and the polymerization is not dependent upon the formation of disulfide bonds. These studies raise the possibility that antigen-binding soluble T cell molecules might belong to a new family of immunoproteins, that is related to, but distinct from, classical immunoglobulins and αβ or γδ heterodimers.

Synthesis of two polypeptide subunits of an aminoacyl tRNA synthetase as a single polypeptide chain.

E. coli aminoacyl tRNA synthetases are typically comprised of a single type of polypeptide chain. Glycine tRNA synthetase is an exception, and is comprised of two different subunits. Previous work showed that glyS encodes both subunits in a tandem arrangement of coding regions which are in the same reading frame. Nine nucleotides separate the TAA stop of the first coding segment (alpha-subunit) from the ATG start of the second one (beta-subunit). A plasmid containing glyS was put into four different ochre suppressor strains. In three of them, significant quantities of an alpha-beta fusion protein were synthesized in maxicells, in genetic backgrounds which retained cellular proteases. This shows that the fusion protein is stable in vivo and suggests that Gly-tRNA synthetase is operationally a single polypeptide which is the ancestor of the two subunits.

Wild-type and mutant forms of the pyruvate dehydrogenase multienzyme complex from Bacillus subtilis.

A simple procedure is described for the purification of the pyruvate dehydrogenase complex and dihydrolipoamide dehydrogenase from Bacillus subtilis. The method is rapid and applicable to small quantities of bacterial cells. The purified pyruvate dehydrogenase complex (s0(20),w = 73S) comprises multiple copies of four different types of polypeptide chain, with apparent Mr values of 59 500, 55 000, 42 500 and 36 000: these were identified as the polypeptide chains of the lipoate acetyltransferase (E2), dihydrolipoamide dehydrogenase (E3) and the two types of subunit of the pyruvate decarboxylase (E1) components respectively. Pyruvate dehydrogenase complexes were also purified from two ace (acetate-requiring) mutants of B. subtilis. That from mutant 61142 was found to be inactive, owing to an inactive E1 component, which was bound less tightly than wild-type E1 and was gradually lost from the E2E3 subcomplex during purification. Subunit-exchange experiments demonstrated that the E2E3 subcomplex retained full enzymic activity, suggesting that the lesion was limited to the E1 component. Mutant 61141R elaborated a functional pyruvate dehydrogenase complex, but this also contained a defective E1 component, the Km for pyruvate being raised from 0.4 mM to 4.3 mM. The E1 component rapidly dissociated from the E2E3 subcomplex at low temperature (0-4 degrees C), leaving an E2E3 subcomplex which by subunit-exchange experiments was judged to retain full enzymic activity. These ace mutants provide interesting opportunities to analyse defects in the self-assembly and catalytic activity of the pyruvate dehydrogenase complex.

The Human Immunoglobulin Genes

The results that I will describe here concern the structure and rearrangement of the genes coding for antibodies in man. A great deal of work was conducted in several laboratories on the analogous genes of mouse. I shall make no attempt to review this work. The human antibody gene system was chosen for study largely because of the existence of a wide range of defined, clinical disorders of the immune system, which include the immunodeficiency diseases (e.g. agammaglobulinaemia) and the leukaemias [frequently tumours of immunoglobulin (Ig) producing cells]. In the preparation and analysis of molecular probes for the immunoglobulin genes, we have gained some knowledge of the arrangement and rearrangement of these genes in man and it is clear that the human antibody genes represent a fluid system which employs a number of highly developed DNA rearrangement procedures in their activation. The antibody proteins are made up from two types of polypeptide chain, the heavy (H) and light (L) chains. Each polypeptide itself has an N-terminal variable (V) region and a C-terminal constant (C) region. The V-region of the heavy (V,) and light (V,) chains together make the antibody combining site capable of specific antigen recognition (defined by the aminoacid sequence of V-regions). The C-region, particularly that of the H-chain (C,), performs more constant functions such as complement fixation. It is the C,-region which defines the antibody class; there are five classes of C,-sequence called p, 8, y, E or a (giving IgM, IgD, IgG, IgE and IgA respectively). The C,-region sequence is invariant in each class except y and a where amino-acid differences define y,, y2, y3 or y, and a, or a, (giving IgG1, 2, 3 or 4 and IgAl or 2 respectively). Any of the H-chain classes or subclasses can associate with either of the two types of L-chain, Kor 12-chains (again defined by their respective amino-acid sequences). During the development of a lymphocyte the first gene to be expressed is p followed by L-chain induction resulting in the formation of surface IgM (Cooper et al. 1976; Knapp et al. 1973: Pernis et al., 1976). A 9-lymphocyte clone can subsequently initiate IgD production, in addition to the IgM it already makes; the two heavy chains involved here (i.e. p and 6) express the same V,-segment A subsequent event occurs, the H-chain class switch, which results in the expression of IgG, IgA or IgE in place of IgM and IgD but maintaining the same antibody combining site (Sledge et al. 1976; Wang et al. 1970). These various events involve a complex set of chromosomal DNA rearrangements. Basically in the germ-line the antibody genes are in pieces and the fully active gene is created, within the B-cells, by these rearrangements.

Separation and chemical differentiation of α and β subunits in yeast phosphofructokinase

The two types of subunits α and β constitutive of yeast phosphofructokinase have been separated by ion-exchange chromatography under denaturating conditions. Amino acid analysis and peptide mapping were performed on the isolated subunits. The frequence of most of the amino acids significantly differs between the two types of polypeptide chains. Moreover, tryptic peptide maps of α and β subunits are clearly not superimposable. These chemical differences seem sufficient to account for the distinct catalytic and regulatory functions of β and α subunits in the yeast phosphofructokinase reaction.

Dimeric and tetrameric hemoglobins from the mollusc Scapharca inaequivalvis: Structural and functional properties

The bivalve mollusc Scapharca inaequivalvis contains in the coelomic fluid erythrocytes with a dimeric (HbI) and a tetrameric (HbII) hemoglobin like the other members of the arcid family. The tetrameric protein is made up from two types of polypeptide chain, while the dimeric protein is made from a single type of chain which differs from the other two in terms of molecular weight and isoelectric point. The optical and circular dichroism spectra show that the heme environment in HbI and HbII resembles that of vertebrate hemoglobins, although distinctive features are present in the deoxygenated derivative. p]The dimeric HbI in the pH range 6 to 9 does not change its association state upon deoxygenation, while the tetrameric HbII polymerizes as indicated by the appearance of a fast peak in the sedimentation velocity patterns. The dependence of the areas and sedimentation coefficients of the fast and slow peaks on protein concentration is characteristic of a rapidly established association-dissociation equilibrium between tetramers and polymers higher than octamers. The pH, ionic strength and temperature dependence of polymer formation indicate that both hydrophobic and ionic interactions stabilize the polymers. The functional properties of HbI and HbII differ. HbI shows co-operative oxygen binding ( h = 1·5) and a constant oxygen affinity ( p 1 2 = 7.8 mm Hg ) over the pH range 5.5 to 9.5. HbII likewise shows co-operativity in oxygen binding ( h = 2·0). Its oxygen affinity at neutral and alkaline pH values is slightly lower ( p 1 2 = 9.1 mm Hg ) than that of the dimeric protein, but becomes higher at pH values below 6.5 due to the presence of an acid Bohr effect. At high protein concentrations, under conditions of extensive polymerization of the deoxygenated derivative, the oxygen affinity is lowered and co-operativity slightly increased. Both phenomena require that the oxygen affinity of the polymer be lower than that of the tetramer, consistent with the predictions of linkage theory.

Region of the C1q molecule involved in the interaction between platelets and subcomponent C1q of the first component of complement

The interaction between platelets and collagen can be inhibited by intact C1q or by a large, collagen-like fragment derived from C1q by limited proteolysis with pepsin (Cazenave et al, 1976; Wautier et al., 1977). C1q is composed of 6A, 6B and 6C polypeptide chains, each of which is approximately 200 amino acid residues long and contains collagen-like regions of approximately 80 amino acid residues (Reid, 1979). Samples containing all, or portions, of the collagen-like regions from each of the three types of polypeptide chains were obtained by either separation of the A, B and C chains after performic oxidation, or by the isolation of large peptides after cyanogen bromide digestion of the intact molecule. These samples were then tested for their ability to inhibit platelet adhesion and platelet aggregation in the presence of type I and type III collagen. It appears probable that the A chain of C1q contains the collagen-like amino acid sequences which are important in the interaction between C1q and platelets.

Purificaton of the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus and resolution of its four component polypeptides.

1. The pyruvate dehydrogenase complex was purified from Bacillus stearothermophilus in high yield. The specific activity (about 40nkat/mg of protein) was substantially lower than that of the pyruvate dehydrogenase complex from Escherchia coli (about 570nkat/mg of protein) measured at 30 degrees C under the same conditions. 2. The relative molecular masses of the four types of polypeptide chain i the complex were estimated by means of sodium dodecyl sulphate/polyacrylamide-gel electrophoresis to be 57 000, 54 000, 42 000 and 36 000 respectively. These polypetide chains showed no evidence of seriously anomalous behavior during tests of electrophoretic mobility. 3. The enzyme complex was resolved into its constituent proteins by means of gelfiltration on Sepharose CL-6B in the presence of 2M-KI, followed by chromatography on hydroxyapatite in the presence of 8M-urea. These harsh conditions were necessary to cause suitable dissociation of the enzyme complex. 4. The amino-acid compositions of the four constituent proteins after resolution were determined and their chain ratios were measured for several preparations of the complex. Some variability was noted between preparations but all samples contained a significant molar excess of the chains thought to contribute the pyruvate decarboxylase (EC 1.2.4.1) activity. 5. From the relative molecular masses and chain ratios of the four constituent proteins, it was calculated that the empirical unit must be repeated at least 50 times to make up the assembled complex. This conclusion is fully consistent with the demonstration by means of electron microscopy of apparent icosahedral symmetry for the Bacillus stearothermophilus complex, implying a 60-fold repeat. The structure stands in sharp contrast with the octahedral symmetry (24-fold repeat) of the Escherichia coli enzyme.