HEMOGLOBIN AND MYOGLOBIN

Breakdown of Diazotized Proteins and Synthetic Substrates by Rumen Bacterial Proteases

Several different kinds of substrate were used to investigate the proteolytic activity of rumen bacteria and of proteases released from rumen bacteria by blending (“coat proteases”). These substrates included diazotized feed proteins and diazotized soluble and insoluble pure proteins. It was concluded that, while solubility was an important factor, the secondary and tertiary structure of a protein had a major influence on its rate of digestion. The resistance of elastin congo red to digestion indicated that similar fibrous proteins in plant material might resist proteolytic attack by rumen bacteria. Coat proteases had a broad specificity, including several exo- and endopeptidase activities, as determined by using synthetic peptide substrates.

Radiolysis of alpha, alpha-trehalose in concentrated aqueous solution; the effect of co-irradiated proteins and lipids

gamma-Radiolysis (dose-rate: 0 X 89 Gy/s) or electron (e)-radiolysis (dose-rate: 5 X 10(7) Gy/s) of unbuffered aqueous solutions of alpha, alpha-trehalose (concentration: 60 mg/ml, radiation dose: 20 kGy) at 0 degree C yielded glucose (Ggamma = 1 X 7; Ge = 0 X 63) and 5-deoxyxylohexodialdose (Ggamma = 0 X 21; Ge = 0 X 05). Buffering at pH-values of 5 X 0 or 5 X 5 and irradiation caused increased formation of these monomeric products, particularly of the deoxy-compound. On addition of increasing amounts of bovine serum albumin or ovalbumin (10-30 mg/ml) and irradiation the yields of products were markedly reduced. The decrease in glucose formation was less pronounced when sperm whale myoglobin was present during gamma- or electron-irradiation. The G-values of 5-deoxyxylohexodialdose, however, were increased by 45 per cent (gamma-irradiation) and 70 per cent (electron-irradiation) at approximately 10 mg/ml of admixed myoglobin. Further increase in myoglobin concentration led to a gradual decrease in the yields of the deoxy-product. The observed effects are explained by scavenging of water radicals and by interactions of the added substrates with sugar radicals. Emulsified lipids (palmitic acid methylester or trilinoleic glycerol) did not affect the radiation-induced formation of products from trehalose.

Interaction of mammalian hemoglobins with dehydroascorbic acid

Reactive sulfhydryl groups of major hemoglobins from guinea-pig, rat and cat reduced dehydroascorbic acid to ascorbic acid leading to formation of intrachain disulfide bonds. Hybridization experiments indicated that the reduction was carried out by the alpha chain of cat hemoglobin.

Isolation of cathepsin D from human leucocytes

Acid and neutral protease activities were determined in the granule fractions of polymorpho and mononuclear leucocytes, separated from human blood by means of a discontinuous density gradient centrifugation. The mononuclear leucocytes contained only acid protease while preparations from polymorphonuclear leucocytes showed a predominant activity at neutral pH with a small peak in the acid range. A separation of the acid from the neutral enzyme could be obtained in the granule fraction of polymorphonuclear leucocytes by means of DEAE chomatography. The acid enzyme was then purified from a mixture of leucocytes, more than 400 times, by means of gel chromatography with Sephadex G-200 superfine. The purified acid protease showed an optimum pH of 3.6, had a molecular weight at 42 000 and was characterized by a single protein band (Rf = 0.31) by disc-gel electrophoresis. With all probability this enzyme can be classified as cathepsin D (EC 3.4.4.23).

The concentration dependence of the hemoglobin mutual diffusion coefficient

Laser correlation spectroscopy was used to measure the mutual diffusion coefficient, D, of human cyanomethemoglobin (Fe+++:CN) at varying protein concentrations. These measurements were made at 20 degrees C in a 0.1 M phosphate buffer solution at pH 7.0. For low protein concentrations we find D = (6.43 +/- 0.26) X 10(-7) cm2/s and that there is a near linear decrease from this value at higher concentrations. The linear relation between the diffusion coefficient and protein concentration allows us to deduce the value of the linear frictional volume fraction coefficient, Kf=7.75, and to extrapolate to hemoglobin concentrations equivalent to that in the red blood cell where we estimate D = 4.25 X 10(-7) cm2/s. Various theoretical predictions of the dependence of the mutual diffusion coefficient on concentration are tested; we find that the generalized Stokes-Einstein relation can be made to fit our high concentration data if we assume a hard-sphere model and if we include a term involving a hydrodynamic interaction integral.

The binding of organic phosphates to human methaemoglobin A. Perturbation of the polymerization of proteins by effectors

Theory is presented relating to the binding of an effector to two states of a protein acceptor coexisting in equilibrium. The problem is treated in terms of the four possible cases which specify relations between numbers of binding sites and intrinsic binding constants relevant to the acceptor states. It is shown that a distinction between these cases may be possible on the basis of the form of a plot of unbound effector concentration versus the constituent equilibrium coefficient which may be calculated from the sedimentation coefficient of the protein constituent. Particularly noteworthy in this respect is the finding that a turning point may exist in this plot for defined conditions with systems in which binding sites are not conserved (and binding affinities are altered) on polymer formation. The latter type of system is exemplified by studies on methaemoglobin A in 0.25 M sodium acetate, pH 5.4. In the absence of added organic phosphate effectors, a dimer-tetramer equilibrium operates governed by an association constant of 4.15 +/- 0.06 X 10(3) 1/mol, determined from sedimentation equilibrium results. Correlation of sedimentation velocity and equilibrium results shows that addition of adenosine 5'-triphosphate (ATP) results in its binding to one site on each of the dimeric (alpha beta) and tetrameric (alpha beta)2 species with intrinsic binding constants 1.03-10(3)-1.20-10(3) and 1.1-10(4)-2.1-10(4) 1/mol, respectively. It is also shown that 2,3-diphosphoglycerate perturbs the dimer-tetramer equilibrium in a similar way to ATP.

Gel filtration studies on oxyhemerythrin. II. Effect of temperature and ionic strength on the association-dissociation equilibria

The effects of temperature and ionic strength on the association of oxyhemerythrin have been studied. deltaH degrees and deltaS degrees for association at pH 7.0 are -2.6 kcal and +16.5 eu per mol of monomer. These values suggest that solvent adjacent to the surface of the protein undergoes rearrangement on association. Increasing ionic strength is observed to promote dissociation while decreasing the rate of attainment of equilibrium between monomers and octamers. Qualitatively similar results are observed on lowering the pH from 7.0 to 4.8, thereby linking the effects of increasing ionic strength to those of protonation of specific amino acid residues at the subunit contacts of hemerythrin. The apparent enthalpy of ionization of the amino acid residue controlling dissociation at acidic pH was found to be -1.9 to +2.1 kcal/mol. These values are consistent with a carboxyl group.

Degree of dissociation of apohemoglobin studied by nano-second fluorescence-polarization technique

A fluorescent dye 1-anilino-8-naphthalene sulfonate was complexed with human apohemoglobin and sperm whale apomyoglobin. Nanosecond fluorescence-polarization kinetics were measured for each of these complexes in KC1 solutions to obtain their fluorescence lifetimes and rotational correlation times. The rotational correlation time of apohemoglobin-dye complex was found to be 21 ns, which was about twice that of apomyoglobin-dye complex, 11 ns. These values were constant over an ionic strength range from 0 to 1.7. Circular dichroism spectra (215-300 nm) and fluorescence lifetimes of the complexes were also found to be independent of the ionic strength, indicating that no gross conformational change occurs with the change in the salt concentration, These results suggest that apohemoglobin remains dimeric over the ionic-strength range examined.

Oxygen equilibrium and subunit aggregation of a holothurian hemoglobin

The hemoglobin of the sea cucumber Cucumaria miniata Brandt has a mol. wt of about 36000 in the oxy- form with a s20,w equal to 2.9 and a subunit molecular weight of 18000 by sodium dodecylsulfate gel electrophoresis. This pigment aggregates when deoxygenated to an oligomer with a s20,w equal to 4.7, an aggregation which is reversible upon subsequent oxygenation. The hemoglobin shows a sigmoid binding equilibrium with "n" equal to 1.8 and a decrease in oxygen affinity with an increase in pigment concentration. This hemoglobin is compared with other hemoglobins showing oxygenation-linked subunit aggregation.

Urea tolerance as a molecular adaptation of elasmobranch hemoglobins

Urea is maintained at moderately high concentrations in the blood and tissues of marine elasmobranchs. Functional properties of the hemoglobins fromn several elasmobranch species are unaffected by urea concentrations as high as 5 molar. This in. sensitivity to urea, which is not observed with human hemoglobin, is accompanied by an increased sensitivity to sodium chloride.

Synthesis of the myoglobin active site

A simple heme-imidazole compound, having the same geometry as the heme-imidazole complex in myoglobin, has been synthesized. This compound, ferropyrroporphyrin-N-[3-(1-imidazolyl)propyl]amide, reversibly binds oxygen in the solid state or when dissolved in a polystyrene film. These results suggest that the principal factors governing reversible oxygen binding are the electronic nature of the base (imidazole), neighboring-group effects of the basic group, and immobilization of the heme group.