Types Of Polypeptide Chains Research Articles

Biological Activities of Immunoglobulins of Different Classes and Subclasses

This chapter discusses the biological activities of immunoglobulins of different classes and subclasses. This chapter illustrates that all immunoglobulins are composed of two types of polypeptide chains, heavy and light, which are linked by disulfide bonds. The biological activities of immunoglobulins may be divided into two categories: (1) the specific reaction with antigen and (2) the consequences of antigen - antibody reactions. The reaction with antigen has been called the primary function of immunoglobulins and is a property of the Fab fragment. This chapter reviews the biological activities that follow antigen-antibody reactions and that have been called the secondary functions of immunoglobulins. It has now been shown that the antibodies of the various classes and subclasses differ in their biological activities, and, in the future, one should attempt to determine how frequently restricted immune responses occur and how important such restricted antibody formation is in immune deficiency syndromes.

Purification and Characterization of a Lecithin-d(-)-β-Hydroxybutyrate Dehydrogenase Complex

Abstract A complex between partially purified d(-)-β-hydroxybutyrate dehydrogenase from beef heart mitochondria and soybean lecithin was purified. The active complex contains a single type of polypeptide chain of molecular weight 32,000 as determined by sodium dodecyl sulfate-acrylamide gel electrophoresis. The amino acid composition of the polypeptide chain is similar to that of many soluble enzymes, despite the very strong interaction with lecithin vesicles which was demonstrated. Cross-linking experiments with dimethyl suberimidate dihydrochloride failed to disclose any polypeptide aggregates in the enzyme-lecithin complex. The apparent Michaelis constants for all four substrates and the temperature dependence of the initial velocity were determined for the purified complex.

Multivalent Feedback Inhibition of Aspartokinase in Bacillus polymyxa: IV. ARRANGEMENT AND FUNCTION OF THE SUBUNITS

Abstract Aspartokinase of Bacillus polymyxa is composed of equimolar amounts of two types of polypeptide chain, α and β, with molecular weights of about 43,000 and 17,000, respectively. Analysis of the products formed after partial crosslinking with dimethyl suberimidate supports a structure of the type α2β2 and suggests a subunit arrangement defined by only two different bonding domains, one of the type α—α and one of the type α—β, with no interaction between the β subunits. The enzyme can be reversibly dissociated by treatment with 4 m urea, and the α and β chains have been separated by gel filtration on Sephadex G-200 in the presence of the denaturant. Upon removal of urea, the α subunit aggregates to a series of even-numbered oligomers, the β subunit forms dimers, whereas mixtures give rise to the tetramer α2β2. This pattern of aggregation is consistent with the postulated subunit arrangement. Renatured preparations of α subunit regain a low level (20%) of aspartokinase activity which is uniformly associated with all oligomeric forms and whose catalytic and allosteric properties are indistinguishable from those of native aspartokinase. This implies that the catalytic center as well as the three types of allosteric sites (for l-threonine, l-lysine, and nonpolar l-amino acids) all reside on the α subunit, and that the conformation of the α dimer is not constrained by association with itself or with β subunit. When α subunit is renatured in the presence of β subunit, a higher level (60%) of aspartokinase activity is recovered. The stimulation of reactivation is a hyperbolic function of the square of the relative β concentration and requires the presence of β subunit during the refolding process. These results suggest that the β subunit of aspartokinase does not participate in catalysis, regulation, or maintenance of structure, but rather that it may function during the folding or maturation of the enzyme.

Studies on Human Secretory Immunoglobulin A.

Abstract Human secretory IgA (S-IgA) from colostrum contains 8.7% carbohydrate consisting of 0.7% fucose, 2.6% mannose, 1.6% galactose, 2.5% glucosamine, 0.2% galactosamine, and 1.1% sialic acid. The carbohydrate content is unevenly distributed among the polypeptide chains. Assuming that the S-IgA is composed of four heavy (H) chains, four light (L) chains, one secretory component (SC) and one J chain, the total carbohydrate content would be distributed as follows: 63% in H chains, 28% in SC, 6.5% in J chain, and 2.5% in L chains. The qualitative composition and the ratio between individual carbohydrates is similar in the different types of polypeptide chains, with the two following exceptions: galactosamine was found only in H chains and a higher content of fucose was detected in SC than in the rest of the chains.

Structures and Function of Immunoglobulins and Some Disorders of Synthesis.

Excerpt All immunoglobulins consist of two types of polypeptide chains (heavy and light chains) that appear to be under separate genetic control. Certain neoplastic disorders of plasma cells and ly...

Multivalent Feedback Inhibition of Aspartokinase in Bacillus polymyxa: III. PURIFICATION AND SUBUNIT STRUCTURE OF THE ENZYME

Abstract Aspartokinase has been purified approximately 1,300-fold from crude extracts of Bacillus polymyxa. Electrophoresis in polyacrylamide gels and equilibrium ultracentrifugation indicated that the purified enzyme was essentially homogeneous. Aged preparations of the enzyme exhibit two electrophoretic components which can be interconverted by treatment with the feedback inhibitors l-threonine and l-lysine or with MgCl2. The molecular weight and partial specific volume were determined by equilibrium ultracentrifugation to be 116,000 and 0.751 ml per g, respectively. The amino acid composition of the enzyme was analyzed. Upon electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulfate or urea or after treatment with maleic anhydride, aspartokinase could be resolved into two components of molecular weights about 17,000 and 47,000, respectively. The two types of subunits could be separated be gel filtration on Sephadex G-200 in the presence of sodium dodecyl sulfate. It is concluded that aspartokinase is an oligomeric protein composed of at least two different types of polypeptide chains.

Structural and Molecular Weight Studies on the Small Copper Protein, Plastocyanin

Abstract The plastocyanin from Phaseolus vulgaris has been shown to consist of a single polypeptide chain of 100 residues to which 1 atom of copper is bound. This plastocyanin is the smallest copper-protein yet reported; its molecular weight is 10,690. The molar extinction coefficient (e597) of the copper chromophore was shown to be 4.5 x 103. The copper content and molecular weight contrast with that of plastocyanin preparations from spinach (mol. wt., 21,000) and Chenopodium album (mol. wt., 11,500), which both contain 2 copper atoms (2, 13). Amino acid analysis indicated that the minimum molecular weight of the polypeptide chain is 10,626. The dansyl-Edman procedure showed that plastocyanin has only the one NH2-terminal sequence, Leu-Glx-Val-Leu, and reduction and carboxymethylation of the apoprotein gave a homogeneous product, as judged by acrylamide gel electrophoresis and Sephadex gel chromatography. The molecular weight of the carboxymethyl protein was similar to the minimum molecular weight value of 10,626. There are 2 residues of methionine per minimum molecular weight, and cyanogen bromide cleavage of the carboxymethyl protein gave 3 fragments, containing 58, 35, and 7 residues. The characterization of these peptides confirmed that the protein contains only one type of polypeptide chain, with a molecular weight of 10,626. Molecular weight values for the native protein of about 11,000 were consistently obtained by Sephadex gel chromatography in sodium acetate buffers at pH 6.0 and of varying ionic strengths. The approach to equilibrium technique yielded a value of 10,790 in sodium acetate buffer, pH 6.0. Variable and high molecular weight values for plastocyanin (up to 16,000) were obtained by Sephadex gel chromatography in sodium phosphate buffers. The reason for these anomalous values is not clear. Frontal analysis studies with Sephadex did not indicate dimerization of the molecule in the phosphate buffer. There was no significant difference in the molecular weight or sedimentation coefficient of plastocyanin in acetate and phosphate buffers as judged by ultracentrifugation.

Molecular properties of acetylcholinesterase

The molecular weight of acetylcholinesterase (acetylcholine hydrolase, E.C. 3.1.1.7) has been determined by sedimentation equilibrium and found to be 260,000. The enzyme is split in the presence of guanidine and mercaptoethanol into four subunits, each having one fourth of the molecular weight of the native enzyme. Examination of the C-terminal residues by two independent methods, namely hydrazinolysis and enzymic hydrolysis by carboxypeptidase A, revealed that there are two types of polypeptide chains in acetylcholinesterase. This suggests that acetylcholinesterase has a dimeric hybrid structure, with two α and two β chains.

Electrophoretic Behaviour of H and L Chains of Human Serum and Colostrum Gamma-globulin

DISSOCIATION of gamma-globulin molecules by reduction in urea with such thiol reagents as mercapto-ethanol and thioglycolate1,2, or in neutral aqueous solution3, or by S-sulphonation4,5, allows the identification of two types of polypeptide chain, called H, (A) and L (B), which may be separated by gel filtration.

Contribution to the structural characterization of gamma globulin from pig colostrum.

From the results obtained in the present work it is concluded that gamma globulin of the 7 S type (γG) which represents the main immunoglobulin component of pig colostrum, differs from serum γG globulin by the presence of another type of polypeptide chain, designed L2; the latter was detected after S-sulfonation in starch gel electrophoresis as the fastest moving component and its immunoelectrophoretic pattern shows the presence of two precipitating components.

STRUCTURAL STUDIES OF HUMAN 7S γ-GLOBULIN (G IMMUNOGLOBULIN)

1. Detailed physical, chemical, and immunologic studies of a protein closely related to the Fc fragment and heavy chain of G immunoglobulin (IgG), and elaborated by a subject with a lymphoproliferative disorder are presented. 2. The protein, which has a molecular weight of 51,000, was cleaved into two half molecules by reduction and alkylation. 3. The protein has few if any of the antigenic determinants of the antigen-binding (Fab) papain fragment of IgG, and has a striking similarity in its antigenic properties to the Fc fragment. 4. Fingerprint patterns resemble those of the crystallizable (Fc) fragment, and lack several peptides found in the heavy chain. 5. These findings suggest that the Fc fragment may be a real structural unit of IgG, and raise the possibility of the existence of three different types of polypeptide chains in G immunoglobulin.

THE RELATION BETWEEN STRUCTURE AND FUNCTION IN HEMOGLOBINS.

Many lines of evidence indicate that the oxygenation of hemoglobin is accompanied by changes in protein structure. Data on the oxygen equilibria of the hemoglobins from a number of animals are discussed in terms of this evidence. Evidence from studies of some hemoglobins (lamprey, frog and tadpole) indicates a major role for subunit dissociation equilibria in explaining two properties of the oxygen equilibria: heme–heme interaction and the "Bohr effect". The importance of subunit dissociation in mammalian hemoglobins is suggested by the known concentration dependence of the oxygen equilibria. Mammalian hemoglobins are composed of two types of polypeptide chains, α and β. The idea that the α and β subunits have different oxygen equilibria and are affected differently by pH is examined. It is concluded that the β-chains appear to play a major role in the mechanism of the Bohr effect not shared by the α-chains. This conclusion is supported by the structural changes in hemoglobin found to occur upon oxygenation by X-ray diffraction techniques.

Formation of Ferrihæmoglobin of Isolated Human Hæmoglobin Types by Sodium Nitrite

THE sensitivity of haemoglobins to oxidation by potassium ferricyanide and sodium nitrite (NaNO2) has been examined extensively1,2. During treatment of oxyhaemoglobin with NaNO2, both components are oxidized through a combination of different reactions, the total reaction being summarized as follows: NaNO2 + 2R–Fe++ O2 + H2O→NaNO3 + 2R–Fe+++OH + O2 (ref. 2). The rate of ferrihaemoglobin formation by the action of NaNO2 can be calculated from the sigmoid curve representing the relation between reaction time and per cent of ferrihaemoglobin and is expressed as the time required for 50 per cent oxidation of the haemoglobin (T 1/2). It has been demonstrated that the haemoglobin of cord red blood cells, which is composed mainly of fœtal haemoglobin (Hb-F), is particularly sensitive to treatment with NaNO2. Since the structural difference between Hb-F and Hb-A is located in one of the two types of polypeptide chains, Hb-F being composed of 2 α-chains and 2 γ-chains (α2γ2) and Hb-A of 2 α-chains and 2 β-chains (α2β2), the possibility is present that NaNO2 will react differently with human haemoglobin types of other structural composition.

Absence of haemoglobin A2 in an adult.

HAEMOGLOBIN A2, the minor component of normal adult haemoglobin, amounts to about 2.5 per cent of the total haemoglobin; it can be distinguished from the major adult component, haemoglobin A1, by its electrophoretic and chromatographic properties. Recent investigations have shown that haemoglobin A2 consists of two types of polypeptide chains: the α-chain, identical with the α-chain of haemoglobins A1 and F, and the δ-chain, which differs in constitution from the corresponding chains of haemoglobin A1, (the β-chain) and F (the γ-chain)1,2. A two-fold increase of the normal percentage of haemoglobin A2 occurs in the usual type of β-chain thalassaemia trait, prevalent in Greece3, while a decrease is observed in haemoglobin-H disease. A decrease of the A2 fraction down to 1 per cent has been observed as a reversible phenomenon in iron-deficiency anaemia4. Traces of haemoglobin A2 can be detected in cord blood haemoglobin by the application of special techniques.

The Arrangement of Amino Acids in Proteins

Publisher Summary This chapter focuses on the accuracy of the peptide theory and on the possible existence of non- peptide bonds in proteins. Partition chromatography in the form of paper chromatography is a method that is identified as breakdown products of proteins where more peptides are used. This technique had been identified by the classical methods of organic chemistry. Three types of polypeptide chains are possible, open, cyclic and branched. There are two types of terminal residues, those with a free amino group and those with a free carboxyl group. The Dinitrophenyl (DNP) method is used for the separation and identification of peptides containing lysine. Elution can be effected with acid ethanol and the peptides subsequently fractionated on suitable partition chromatograms. The theoretical possibility exists that synthetic reactions may occur during the partial hydrolysis of proteins. Acid hydrolysis is the most used method of degrading proteins, and it is almost universally employed when amino acids are to be isolated or estimated, since it leads to complete hydrolysis with a minimum of destruction. Paper chromatography is preferred for the final fractionation of a simplified peptide mixture because of the good resolutions obtained, the ease and rapidity of technique, and the possibility of using the two-dimensional method. The chief disadvantage is that only a very small amount of each peptide can be obtained from a chromatogram, though it is usually possible to obtain sufficient material to determine the structure of di- and tri-peptides.