1. Potentiometric circular dichroism titrations of cytochrome c oxidase, carried out in the absence of cytochrome c, confirm the potentiometric equivalence of the two heme a groups of cytochrome c oxidase. In the presence of cytochrome c, two different midpoint potentials are found for the two heme a groups of cytochrome c oxidase.2. Circular dichroism difference spectra (reduced minus oxidized) of the two heme a components of cytochrome c oxidase have been obtained by means of this potentiometric titration. On reduction of the first heme a group a circular dichroism difference spectrum is obtained with peaks at 425, 442 and 602.5 nm; the second heme a group shows difference peaks at 434, 447 and 608 nm. Whereas both heme a groups contribute about equally to the absorbance difference spectrum, the second heme a group reduced contributes about twice as much to the circular dichroism difference spectrum as does the first heme a group.3. From these spectral and circular dichroism differences it is concluded that, on reduction of or ligand binding to cytochrome c oxidase, conformational changes occur which affect the symmetry of the environments of the heme a groups.

A series of poly( L ‐glutamic acid) esters have been synthesized and studied by optical rotatory dispersion, x‐ray diffraction, and infrared spectrometry. The results obtained emphasize the importance of the outer portions of the side chains in determining both the stability and precise conformation of the α‐helix.

A series of poly( L -glutamic acid) esters have been synthesized and studied by optical rotatory dispersion, x-ray diffraction, and infrared spectrometry. The results obtained emphasize the importance of the outer portions of the side chains in determining both the stability and precise conformation of the α-helix.

A series of polypeptides containing ordered sequences of glyeyl and γ‐ethyl L ‐glutamyl residues has been synthesized. The properties of the polymers were investigated by x‐ray diffraction, infrared spectrophotometry, and optical rotator dispersion, and the results indicate that glycine appreciably reduces the stability of the γ‐ethyl L ‐glutamate helix.

1.1. The morphological parts of the feathers from six species of birds are distinctly dissimilar in amino acid composition but the most abundant amino acids are always glycine, serine and proline and there is almost a complete absence of lysine, histidine and methionine in all cases.2.2. An examination of the soluble S-carboxymethyl-proteins of the parts of the different species by moving-boundary and gel electrophoresis shows them all the heterogenous, with marked differences both between species and between the parts of one species.3.3. Solutions of S-carboxymethyl feather keratins undergo spontaneous separation into fractions which differ in their electrophoretic and amino acid compositions.

1. The low sulfur fraction of S-carboxymethyl wool keratin, which has an α-helix content of about 50% in aqueous solution, has been subjected to partial proteolysis with the enzyme Pronase P to yield an acid-precipitable fraction with a helix content of about 85%. 2. The optimum conditions for the preparation of this fraction have been studied with respect to time, temperature, pH, enzyme concentration, and Ca++ concentration. 3. In dilute solution the material appears to consist chiefly of particles with a molecular weight of about 41,000 and an axial ratio of 8:1 to 10:1. The dimensions are consistent with a multistranded, rod-like particle made up of probably three α-helical chains. 4. In 8 m urea, the particles break down irreversibly to a heterogeneous mixture, with molecular weights in the range 2000 to 5000, which suggests that peptide bonds are broken in the helical segment during proteolysis, but the integrity of the particle is maintained by its multistranded structure. Both gel chromatography and gel electrophoresis indicate that the helix-rich particle is derived from the major helical components of the low sulfur fraction of S-carboxymethyl wool keratin. 5. Amino acid analysis of the helix-rich fraction shows that, compared to the low sulfur fraction of S-carboxymethyl wool keratin, it is enriched in the helix-favoring residues lysine, leucine, alanine, and glutamic and aspartic acids and depleted in the helix-inhibiting residues S-carboxymethylcysteine, proline, serine, threonine, and glycine.

A series of polypeptides containing ordered sequences of S-benzyl-L-cysteinyl (C) and γ-ethyl-L-glutamyl (G) residues has been synthesized. Optical rotatory dispersion measurements show that all the polymers adopt some degree of helical conformation in solution. Using polarized infra-red spectrometry α-helical material could be detected in films of all the polymers, as in solution, but always in lower amount than in the parent (G2)n homopolymer†. The polymers (G3CG)n, (GCG)n and (GCG2)n gave α-type X-ray diffraction patterns; the remainder gave β-type patterns. In general the stability of the α-helix is lowered by the introduction of C residues. It is suggested that this is due to an unfavourable side chain—main chain interaction.

The optical-rotatory dispersion and viscosity properties of poly-S-carbobenzoxy-methyl-l-cysteine have been studied in mixtures of dichloroacetic acid and ethylene dichloride. As the proportion of the more polar solvent increases there is a large increase in the intrinsic viscosity [η] and large decreases in the specific optical rotation [α]λ and the parameter a0 calculated from the Moffitt-Yang equation. The changes in these properties occur over such a narrow range of solvent composition as to suggest that a cooperative transition is occurring between two molecular forms. However, there is no change in the optical-rotatory constant b0, indicating that the transition is not one between a helical and a random-coil conformation. The changes observed with this polypeptide are typical of those which occur during the denaturation of such globular proteins as β-lactoglobulin and γ-globulin which are also characterised by the absence of appreciable helical contents in their native states.

The binding of three acid dyes of slightly differing composition to a soluble wool keratin derivative has been measured by the dialysis-equilibrium method. The data satisfy the Klotz-Scatchard equation for the binding of small ions to proteins but the maximum amount of dye bound is much less than that equivalent to the number of basic side chains on the protein, given by amino acid analysis. It seems likely that the guanidino groups of the arginine residues are not able to bind dye anions, and it is suggested that this occurs because they are more firmly bound to other groups on the protein. Intermolecular bonding of this type would account for the high degree of aggregation shown by the soluble wool protein. The influence of pH and ionic strength on the binding of the three dyes is discussed in relation to their chemical structure.

The influence of pH and ionic strength on the molecular weight of insulin, measured by the surface balance technique, has been studied. The balance employed was considerably more sensitive than that used by Fredericq in a previous study, and it enabled measurements to be made at much lower surface concentrations. The value of ∼ 6000 for the molecular weight of insulin spread on 0.01N hydrochloric acid found by Fredericq has been confirmed. However, at higher pH values, where Fredericq observed increased molecular weights, it is shown that at very low surface concentrations the molecular weight tends towards ∼ 6000, association being favored as the surface concentration is increased. An increase in ionic strength is shown to have different effects at the isoelectric point and at pH values removed from this point; in the former case it has a dissociating effect and in the latter, an associating effect, although at infinite dilution the molecular weight tends to ∼ 6000. These effects and that of pH are discussed in terms of the Coulombic and non-Coulombic forces operating in the system.

The pressure-area and surface potential-area curves for insulin at the air-water interface have been determined over a considerable range of subsolution pH and ionic strength. The area of first collapse of the protein has been found independent of either of these factors, indicating that complete spreading has been achieved over the range studied. This area corresponds to the area per residue for a crystalline protein in the β configuration. The surface pressure is shown to be a minimum at the isoelectric point of the protein (pH 5.7), providing a method for determining the latter for proteins insoluble at this point. The balance between Coulombic and non-Coulombic bonding is considered in an attempt to explain the effects of pH and ionic strength on the surface pressure- and surface potential-area curves. The curve of pH vs. surface potential at constant area is shown to be analogous to the usual electrometric titration curves for proteins.