Ephraim Katchalski

Poly-α-Amino Acids

Publisher Summary Poly- α -amino acids are obtained by the polymerization of amino acids or their suitable derivatives, serving as monomers. Like other synthetic polymers, they represent a mixture of macromolecules of varying chain lengths. This chapter deals with the synthetic poly- α -amino acids, with emphasis on α -amino acid residues in normal peptide linkage. Essentially, synthesis of poly- α -amino acids is accomplished by a typical one-step polymerization process in which a polymer of relatively high average molecular weight is obtained. The monomers used for synthesis of poly- α -amino acids include: (1) free α -amino acids, (2) esters of α -amino acids, (3) esters and azides of peptides, and (4) N-carboxy-α -amino acid anhydrides. The chapter also describes behavior of poly- α -amino acids toward proteolytic enzymes and the physical properties of poly- α -amino acids. Water soluble poly- α -amino acids are also presented. The X-ray study of synthetic polyamino acids is one of the possible approaches to the wider problem of the structure of natural proteins. Information about the packing arrangements of peptides can also be obtained by X-ray studies. Some polyamino acids can be cast into films or drawn into fibers, which helps in their study in oriented form and in addition allows a comparison of their properties with those of fibrillar proteins.

Synthesis and Chemical Properties of Poly-α-Amino Acids

Publisher Summary The chapter discusses the synthesis and chemical properties of poly-α-amino acids. Poly-α-amino acids are synthetic polymers composed of α-amino acid residues linked by peptide bonds. They are prepared by polymerization of the corresponding monomers and consist, like other synthetic polymers, of mixtures of homologous macromolecules of varying chain length. The preparative methods developed permit the synthesis of a large variety of α-amino acid polymers, in a wide range of average molecular weights. A number of different derivatives of α-amino acids and peptides have been used as monomers for the preparation of poly-α-amino acids; the most suitable and commonly used are the N-carboxy-α-amino acid anhydrides (NCAs). These readily undergo polymerization, with carbon dioxide evolution, to yield the corresponding poly-α-amino acids. The synthesis of amino acid polymers from the monomers may be accompanied by varying amounts of byproducts that should be removed, during the isolation and purification of the polymer. The purification techniques applied are described in the chapter. In addition, the methods used to establish the chemical constitution of the polymers and their average molecular weights are given.

Theoretical Analysis of the Role of Diffusion in Chemical Reactions, Fluorescence Quenching, and Nonradiative Energy Transfer

The kinetics of diffusion‐controlled chemical reactions in solution are analyzed by a statistical treatment. To start with, the probability of interaction of two molecules A and B, separated by a given distance at zero time and undergoing Brownian motion subsequently, is determined. The probability of interaction of an A molecule with one of many surrounding B molecules is then deduced. Finally, the course of reaction between A and B molecules distributed at random at zero time in a system containing a large number of molecules of both species, is calculated. The treatment outlined is readily extended to systems in which factors other than random diffusion are operative, as well as to systems in which the distribution of A and B molecules is not random at zero time. A few examples are discussed in detail. The theoretical treatment presented is applied to the kinetics of quenching of electronically excited molecules by collision with quencher molecules in solution, and to the calculation of the extent of n...

Lymphocyte transformation induced by concanavalin A and its reversion by methyl-α-d-mannopyranoside

Abstract Concanavalin A induces transformation of rat lymph node lymphocytes by the binding to specific binding sites of the cell membrane. The binding can be reversed by methyl α-D-mannopyranoside. Experiments in which concanavalin A was removed from lymphocytes treated with the lectin at different times of incubation, revealed that prolonged contact of the lymphocytes with concanavalin A is required for the induction of blastogenesis.

Polymers of tripeptides as collagen models: II. Conformational changes of poly(L-prolyl-glycyl-L-prolyl) in solution

An ordered sequence polymer of the structure H(Pro.Gly.Pro)n OH was synthesized as a collagen model. Fractionation by gel filtration gave samples of average molecular weights between 1000 and 12,000. The polymer showed in aqueous solution ordered (helical) conformation which could be destroyed by heating or by the addition of a number of salts. Extent of helicity and sharpness of thermal transitions increased with increasing molecular weight. On the basis of optical rotation measurements, it was concluded that the observed structure is of the poly- L -proline II type, stabilized by co-operative hydrogen-bonding leading to side-to-side association of chain sections. The resulting structure is probably the triple-stranded helix observed in the solid state with this polymer, but alternatives (anti-parallel arrangement, double-strand structure) could not be excluded. The results obtained show that the replacement of every third proline residue in poly- L -proline by a glycine residue, thus introducing one CONH group per tripeptide unit, is sufficient to stabilize a collagen-like structure in solution as well as in the solid state.

Kinetic behavior of a two-enzyme membrane carrying out a consecutive set of reactions.

Abstract A theoretical analysis of the kinetic behavior of a two-enzyme membrane carrying out two consecutive reactions is presented. The behavior of the immobilized enzyme system is compared to that of an analogous system consisting of the two enzymes in solution. The analysis of the immobilized enzyme system is based on the assumption that a quasi-stationary state is established within the unstirred layer at the membrane-solution interface. At this state, the rate of flow of the product formed by the first enzyme into the bulk of the solution, equals the difference between the rate of its production and the rate of its consumption by the second enzyme. The following boundary conditions were chosen in the kinetic analysis presented: (a) the activity of the first enzyme is independent of the second, (b) the enzymic reactions follow first order kinetics, (c) the concentration of the substrate of enzyme 1 is constant throughout the enzymic reaction, (d) the concentration of the products of both enzymic reactions are time dependent, (e) the system is of a finite volume. The effect of the kinetic parameters and of the physical characteristics of the system on its kinetic behavior are examined. It is shown that for all of the hypothetical systems that were analyzed the concentrations of the products of enzyme 1 and 2 in the bulk of the solution, P b 1 and P b 2 respectively, increase linearly with time at least for the first 10 minutes of reaction. For systems which consist of enzymes of relatively high activity, the enzymic reactions are diffusion controlled; the activity of enzyme 1 is limited by the rate of diffusion of substrate from the bulk of the solution, and the activity of enzyme 2 approaches that exhibited by enzyme 1. An analysis of a corresponding homogeneous system containing both enzymes in solution reveals the appearance of an initial lag period in the production of P b 2 . The length of the lag period is determined by the catalytic as well as the physical parameters of the system. In the systems studied, the concentration of P b 1 approaches with time a limiting value. The higher the activity of the two enzymes the sooner the stationary state with respect to P b 1 is reached, and the value of P b 1 is lower. The rate of production of the end product at the first stages of the reaction is markedly higher in the immobilized enzyme system than that predicted for a corresponding homogeneous system.

Biological Properties of Poly-α- Amino Acids

Publisher Summary This chapter attempts to summarize the biological properties of poly-α-amino acids. The data already available indicate that these synthetic polypeptides may be of considerable value in the elucidation of the mode of action of known proteolytic enzymes, in the search for new proteolytic enzymes, and in the clarification of the inhibition of enzymes by macromolecules. It reviews that the close resemblance between the antibacterial and antiviral properties of basic polyamino acids with those of some natural peptides indicates that both the synthetic model compounds and the natural materials may act biologically by a similar mechanism. Also promising are the results obtained in the investigation of the immunological properties of synthetic poly-cu-amino acids and of polypeptidyl proteins, since they may contribute to the understanding of the chemical basis of the antigenicity of proteins. Finally, it is worth mentioning that water-soluble poly-a-amino acids represent one of the few types of synthetic polymers whose biological activity has been investigated in some detail. The extension of such studies to other synthetic water-soluble polymers may, perhaps, lead to the finding of new specific biological reagents. The chapter concludes that it should be stressed that the great value of synthetic poly-α-amino acids as protein models lies in their simplicity relative to the complexity of the natural proteins. Thus, many physical, chemical, and biological properties can be studied, as it were, in isolation by using such synthetic polypeptides. It should be remembered that this same simplicity imposes a limit on the usefulness of these substances, since certain properties, at least, of proteins may derive from a complexity of sequence and structure not found in the synthetic models.

Use of water-insoluble enzyme derivatives in biochemical analysis and separation

SummaryA brief review of the most commonly employed preparative procedures for water-insoluble enzyme derivatives is given, followed by a description of the various factors which can affect the behaviour and the apparent kinetic parameters of an immobilized enzyme system. Current developments in the application of water-insoluble enzyme derivatives in biochemical analysis and separation are dealt with.ZusammenfassungEin Überblick über die gebräuchlichsten Methoden zur Herstellung wasserunslöslicher Enzymderivate wird gegeben. Anschließend werden die verschiedenen Faktoren beschrieben, die das Verhalten und die scheinbaren kinetischen Parameter eines immobilisierten Enzymsystems beeinflussen. Die Anwendungsmöglichkeiten wasserunlöslicher Enzymderivate in der biochemischen Analytik werden besprochen.

Inhibition of lysozyme by imidazole and indole derivatives

Abstract Imidazole, 4(5)-imidazole acetic acid, histidine, histidine methyl ester, and histamine, at varying concentrations, were found to inhibit the lysis by lysozyme of Micrococcus lysodeikticus cells or cell walls. From the pH profile of the extent of inhibition it is deduced that the enzyme is inhibited mainly by the protonated imidazole ring. Inhibition of lysozyme by imidazole or by the imidazole derivatives investigated was accompanied by a decrease in fluorescence intensity of the enzyme. Lysozyme activity could also be inhibited by 3-indole derivatives such as 3-indole propionic acid and tryptamine. The formation in aqueous solution of complexes of the charge-transfer type between compounds containing an indole ring and compounds containing a protonated imidazole ring has been demonstrated by a fluorescence quenching method, and by two thermodynamic methods. Compounds containing a protonated imidazole ring were shown to quench the fluorescence of indoles and to increase their solubilities in aqueous solution. From the temperature dependence of the association constants, enthalpies of association, ΛH, of about −3 Kcal per mole were calculated for the complexes indole-imidazole·HClO4, 3-methyl indole-imidazole·HClO4, indole-histidine·HClO4, and 3-methyl indole-histidine·HClO4. In view of the results obtained with lysozyme and with the low molecular weight model systems, it is suggested that inhibition of lysozyme by compounds containing a protonated imidazole ring is at least partially due to the formation of a charge-transfer complex with the tryptophan residues of the enzyme.

Effect of phytohemagglutinin and prostaglandins on cyclic AMP synthesis in rat lymph node lymphocytes.

Abstract Phytohemagglutinin does not increase the level of cyclic adenosine 3′,5′-monophosphate (cyclic AMP) and does not stimulate adenyl cyclase activity in rat lymph node lymphocytes. N 6 -2′- O -Dibutyryl cyclic AMP stimulates RNA synthesis but does not cause cell transformation. Prostaglandin E 1 markedly increases the accumulation of cyclic AMP and stimulates adenyl cyclase activity of rat lymph node lymphocytes. It does not, however, cause cell transformation. It is tentatively concluded that cyclic AMP does not mediate the effect of phytohemagglutinin in the transformation of rat lymph node lymphocytes.