Ephraim Katchalski

Bio: Ephraim Katchalski is an academic researcher from Weizmann Institute of Science. The author has contributed to research in topics: Amino acid & Trypsin. The author has an hindex of 54, co-authored 131 publications receiving 7545 citations.

Poly-α-Amino Acids

Abstract: 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-alpha-amino acids.

Abstract: 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

Precipitation of arabic acid and some seed polysaccharides by glycosylphenylazo dyes

Abstract: The use of 1,3,5-tri-(p-oc-L-fucosyloxyphenylazo)2,4,6-trihydroxybenzene for precipitation of an L-fucose-binding protein from the seed of Lotu8 tetragonolobu8 (Yariv, Kalb & Katchalski, 1967) revealed that some polysaccharide components present in aqueous extracts of various seeds are precipitated with this dye and with the related glucoside dye 1,3,5-tri-(p-fl-D-glucosyloxyphenylazo) 2,4,6 trihydroxybenzene (Yariv, Rapport & Graf, 1962). We observed that arabic acid is also precipitated with the glucoside dye. In this communication we describe the precipitation reaction and a procedure for the isolation of some seed polysaccharides based on this reaction. Precipitation of arabic acid (Pfanstiehl Laboratories Inc., Waukegan, Ill., U.S.A.) by the glucoside dye was effected at room temperature in 0-1Msodium phosphate buffer, pH6-8, in the range of 5-100 ,g. of polysaccharide/ml. A critical ratio of dye to arabic acid is necessary for precipitation. A plot ofprecipitated dye versus added dye is concave upwards at low dye concentration and becomes concave downwards at higher concentration, eventually reaching an asymptote. The asymptotic value of precipitated dye is proportional to the amount of polysaccharide. In an experiment, glucoside dye was added to each ofa series ofconical test tubes containing 40,ug. of arabic acid in 2ml. After 1 hr. the mixtures were centrifuged and the concentration of dye in the supernatants was measured. Precipitates were observed in all mixtures containing more than 12,ug. of added dye. The saturation value of 41 ,g. of bound dye was reached with 100,ug. of added dye and persisted up to 400,ug. of added dye. With a 1: 1 weight ratio of dye to polysaccharide more than 90% of the polysaccharide was found in the precipitate by means of a procedure described below for the isolation of the dye-binding polysaccharides. The dye did not precipitate arabic acid in 10% (w/v) NaCl or in 8M-urea. Heating an aqueous solution of arabic acid in a boiling-water bath for 1 hr. destroyed its ability to be precipitated with the dye. The following seed materials were used for isolation of the dye-binding polysaccharides: soyabean flour was a defatted product marketed as Soyafluff 200W by Central Soya, Chicago, Ill.,

The anatomy and taxonomy of protein structure.

Abstract: Publisher Summary This chapter investigates the anatomy and taxonomy of protein structures. A protein is a polypeptide chain made up of amino acid residues linked together in a definite sequence. Amino acids are “handed,” and naturally occurring proteins contain only L-amino acids. A simple mnemonic for that purpose is the “corncrib.” The sequence of side chains determines all that is unique about a particular protein, including its biological function and its specific three-dimensional structure. The major possible routes to knowledge of three-dimensional protein structure are prediction from the amino acid sequence and analysis of spectroscopic measurements such as circular dichroism, laser Raman spectroscopy, and nuclear magnetic resonance. The analysis and discussion of protein structure is based on the results of three-dimensional X-ray crystallography of globular proteins. The basic elements of protein structures are discussed. The most useful level at which protein structures are to be categorized is the domain, as there are many cases of multiple-domain proteins in which each separate domain resembles other entire smaller proteins. The simplest type of stable protein structure consists of polypeptide backbone wrapped more or less uniformly around the outside of a single hydrophobic core. The outline of the taxonomy is also provided in the chapter.

Structure of serum albumin.

Abstract: Publisher Summary This chapter provides an insight of the findings of past significant papers with the current knowledge of the recently determined high resolution X-ray structure of serum albumin. The most outstanding property of albumin is its ability to bind reversibly an incredible variety of ligands. The sequences of all albumins are characterized by a unique arrangement of disulfide double loops that repeat as a series of triplets. Albumin belongs to a multigene family of proteins that includes α- fetoprotein (AFP) and vitamin D-binding protein (VDP), also known as G complement (Gc) protein. Although AFP is considered the fetal counterpart of albumin, its binding properties are distinct and it is suggested that AFP may have a higher affinity for some unknown ligands important for fetal development. Domain structure and the arrangement of the disulfides, the surface charge distribution, and the conformational flexibility of the albumin molecule are described. The nature of ligand binding, including small organics, long-chain fatty acids, and metals, to multiple sites on the albumin molecule is clearly depicted. The chapter concludes with the perceptive comments on future directions being taken to explore the structure and function of this fascinating protein.

Conformation of Polypeptides and Proteins

Abstract: Publisher Summary This chapter deals with the recent developments regarding the description and nature of the conformation of proteins and polypeptides with special reference to the stereochemical aspects of the problem. This chapter considers the parameters that are required for an adequate description of a polypeptide chain. This chapter focuses the attention on what may be called “internal parameters”—that is, those which can be defined in terms of the relationships among atoms or units that form the building blocks of the polypeptide chains. This chapter also provides an account of the mathematical method of utilizing these parameters for calculating the coordinates of all the atoms in a suitable frame of reference, so that all the interatomic distances, and bond angles, can be calculated and their consequences worked out. This chapter observes conformations in amino acids, peptides, polypeptides, and proteins.