Anemia in domestic cats: effect on hemoglobin components and whole blood oxygenation.

Phenylhydrazine-induced anemia in the domestic cat results in an increase in minor, high oxygen affinity hemoglobin B components and an accompanying decrease in the major, low affinity B component. This change is accompanied by an unusually large increase in erythrocytic adenosine triphosphate and 2,3-diphosphoglycerate, a slight decrease in the oxygen affinity of whole blood, and a large decrease in the Hill constant.

Inhibition of NADH-methemoglobin reductase by organic phosphates.

The organic phosphate allosteric effectors of hemoglobin, inositol hexaphosphate, 2,3-diphosphoglycerate, and ATP, interact with NADH-methemoglobin reductase (NADH-diaphorase). Significant inhibitory effects on the enzyme were found when dichlorophenolindophenol, or ferricyanide were used as electron acceptors in place of methemoglobin. In contrast, apparent stimulation of enzyme activity was observed when adult human methemoglobin was used as the electroganic phosphate on the rate of reaction due to its interaction with the substrate methemoglobin to produce the favored T type of quaternary conformation. The inhibitory effect of inositol hexaphosphate on the enzyme is associated with a perturbation in the reactivity of essential sulfhydryl group(s) on the enzyme. It is suggested that the interaction of the organic phosphate with the enzyme as well as with the substrate is significant in determining the overall rate of methemoglobin reduction.

Hemoglobin Wood beta97(FG4) His replaced by Leu. A new high-oxygen-affinity hemoglobin associated with familial erythrocytosis.

The characterization of hemoglobin Wood (beta97(FG4) His replaced by Leu), a high oxygen affinity hemoglobin with reduced Hill constant is described. The amino acid substitution occurs at the alpha1beta2 interface, in the same position as in hemoglobin Malmö (beta97(FG4) His replaced by Gln) and in an homologous position when compared with hemoglobins Chesapeake (alpha92(FG4) Arg replaced by Leu) and J. Capetown (alpha92(fg4) arg replaced by Gln).

Comparison of hemoglobins Wood (alpha 2 beta 2 97 leu) and Malmö (alpha 2 beta 2 97 gln). Diagnostic value of citrate agar electrophoresis.

Diagnostic value of citrate agar electrophoresis. Am J Clin Pathol 71:668-671, 1979. Of approximately three dozen hemoglobin variants that have greater than usual oxygen affinity, nearly half are inseparable from hemoglobin A by electrophoresis at pH 8.6. A comparison of hemoglobins Wood (alpha2beta297leu) and Malmö (alpha2beta297gln) is of interest from several standpoints. They represent similar substitutions at the identical locus in the beta chain. They result in identical clinical and hematologic manifestations. Oxygen affinities of these variants are identical. Both are poorly resolved from hemoglobin A by electrophoresis at pH 8.6. The position of each is identical when studied by isoelectric focusing in polyacrylamide gel. Finally, they are easily distinguished by citrate agar electrophoresis at pH 6.2. The excellent resolution of hemoglobins Malmö and Wood from each other results neither from difference in charge, nor size, nor in quaternary structure. This technic provides a simple but effective means for identifying and differentiating these hemoglobin variants. Comparison with the results of citrate agar electrophoresis of other high oxygen-affinity hemoglobins indicates that the findings for hemoglobins Malmö and Wood are unique and unambiguous.

Effects of triethyltin bromide on protein phosphorylation in subcellular fractions from rat and rabbit brain.

Phosphorylation of specific proteins in subcellular fractions of rat brain is affected by the presence of low concentrations (1-50 microM) of triethyltin bromide (Et3SnBr), in vitro. SDS-PAGE and autoradiography showed that Et3SnBr increased phosphorylation of an Mr = 42,000 phosphorylation of an Mr = 52,000 component. The Mr = 42,000 and 76,000-80,000 phosphoproteins have been identified as the alpha-subunit of pyruvate dehydrogenase (PDH) and synapsin, respectively. Et3SnBr-induced phosphorylation of rabbit brain PDH results in partial inactivation of the PDH complex.

Methemoglobin reductase: inactivation and protection against inactivation during disc gel electrophoresis.

Methemoglobin reductase was found to be inactivated during electrophoresis on ammonium persulfate polymerized polyacrylamide gels. Hemoglobin in various states of ligation offers protection from inactivation. Thiols such as dithiothreitol also offer protection but the effect due to hemoglobin is not provided by its sulfhydryl groups.

The amino terminal acetylation of cat globin chains and their tryptic peptides.

Cat blood contains two major hemoglobins, HbA and HbB, both of which are synthesized within the same red cell. They contain identical alpha chains but different beta chains. HbB is somewhat unusual in that it contains beta chains that are modified by N alpha-acetylation. Although the selective amino terminal acetylation of the beta chain of cat HbB occurs during nascent peptide chain growth, it can also occur after completion of globin chain synthesis and its assembly into hemoglobin. However, the latter process is not as efficient as the former, and it occurs non-enzymatically. Two peptides in a mixture of tryptic peptides from cat HbA and non-acetylated cat HbB contain serine at their amino terminus. One is the octapeptide, non-acetylated B- beta T-1, and the other is the tetrapeptide, alpha T-2, derived from both HbA and HbB. We provide evidence here that in a mixture of soluble tryptic peptides, acetylation of alpha T-2 takes place in the presence of acetyl-CoA and ribosomal acetyltransferase at pH 7.0. The amino terminal acetylation requires the presence of an acetyltransferase.

Structural model for the trialkyltin binding site on cat hemoglobin.

The binding site for trialkyltin complexes on the alpha- chain of cat oxyhemoglobins is proposed to involve the SG and NE2 atoms of Cys-13 and His-113 respectively. On deoxygenation, the conformation of this region changes substantially, allowing complexation only through the ND1 nitrogen atom of His-113, a much less favorable interaction. Thus the model presented explains the preferential binding of trialkyltin complexes to R-state cat hemoglobin and suggests the type of interaction that is likely to occur between these compounds and a variety of less well-characterized enzymes to produce the metabolic effects that trialkyltin complexes are known to produce in vivo.

Binding of 2-formylpyridine monothiosemicarbazonato copper II to cat and normal human hemoglobins.

The antitumor agent 2-formylpyridine monothiosemicarbazonato copper(II) forms adducts with sulfur and nitrogen donor atoms from cat hemoglobin but only nitrogen donor atoms from human hemoglobin. Improved resolution of the mI = 1/2 lines in the g parallel region at S-band not only confirms the number of nitrogen donor atoms in the square planar configuration but provides evidence for strong coupling from a proton. Adduct formation results in an increase in the oxygen affinity of hemoglobin. Thus, it is suggested that allosteric enzyme inhibition may be a mechanism for the action of this agent.

Effects of 2-formylpyridine monothiosemicarbazonato copper II on red cell components.

1-Formylpyridine monothiosemicarbazonato copper II (CuL+) is readily taken up by red cells and is initially bound to glutathione and hemoglobin. Glutathione was depleted within 5 hr of incubation, presumably by oxidation mediated by CuL+ and O2 with concomitant generation of toxic oxygen species. Cupric ion was slowly transferred from CuL+ to hemoglobin within about 7 hr and hemoglobin was oxidized until the major form prevailing after 10 hr was alpha 2 beta 2+. Little increase in hemolysis due to addition of CuL+ dissolved in the radical scavenger dimethyl sulfoxide was observed with prolonged incubation. Strong inhibition of red cell hexokinase by CuL+ was observed when the enzymes in red cell lysates and hemoglobin-free red cell lysates were examined. CuL+ was also an effective inhibitor of yeast hexokinase. However, the inhibitory effect of CuL+ within the red cells was less pronounced. It is suggested that even though intracellular accumulation of CuL+ creates an oxidizing environment and is potentially capable of inhibiting thiol enzymes such as hexokinase, protective effects are exerted in the red cell by the presence of hemoglobin, of radical scavengers, and of high levels of enzymes that detoxify toxic oxygen species.

The oxidation of cat, human, and the cat-human hybrid hemoglobins alpha 2 human beta 2 cat and alpha 2 cat beta 2 human by copper(II).

The heme iron of the beta chains of mammalian hemoglobins are rapidly and selectively oxidized in the presence of excess Cu(II) ions in a reaction that requires the presence of a free -SH groups on the beta globin chain. The presence of freely reactive -SH groups on the alpha chains of cat and sheep hemoglobins does not alter the course of this reaction; only the beta hemes are oxidized rapidly by Cu(II) in these hemoglobins. Two equivalents of copper are required for the rapid oxidation of the two beta chain hemes per mole of cat hemoglobin, in contrast with the four equivalents that are required for reaction with human hemoglobin. The human-cat hybrid hemoglobins, alpha 2 Human beta 2 Cat and alpha 2 Cat beta 2 Human, required two and four equivalents of copper/mol, respectively, for the reaction. Thus, the kinetics and stoichimetry of the reaction are determined by the nature of the beta subunit. Analysis of the esr spectra of the products of the reaction of Cu(II) with these hemoglobins indicate that human hemoglobin and the hybrid alpha 2 Cat beta 2 Human contain tight binding sites for two equivalents of Cu(II) that are not involved in the oxidation reaction and are not present in cat hemoglobin or alpha 2 Human beta 2 Cat. Cat beta globin like others (sheep, bovine) that lack the tight binding site, has no histidine residue at 2 beta. It has phenylalanine in this position. These results support the suggestion of Rifkind et al. (Biochemistry 15,5337[1976]) that the tight binding site is near the amino terminal region of the beta chain and is associated with histidine 2 beta.

Interaction between low-affinity cupric ion and human methemoglobin.

Human hemoglobin has been shown to contain a high- as well as a low-affinity binding site for cupric ion on each of its constitutent beta chains. The copper that is bound to the low-affinity site has been implicated in the selective oxidation of the beta hemes. In the present work a low-affinity binding site for cupric ion has been located within 10 A of the heme iron in human hemoglobin. It is suggested that the proximal histidine is involved in the binding of copper at this site and that it participates in the oxidation of heme iron and reduction of cupric ion.

Interaction between bound cupric ion and spin-labeled cysteine beta-93 in human and horse hemoglobins.

The location of the various copper binding sites for horse and human hemoglobin was probed using spin labels attached to the beta-93 cysteine residue. Dipole-dipole interactions between the spin label and bound copper produce a decrease in the amplitude of the spin label spectrum which was used to estimate the Cu(II) spin label distance. By comparing the results with horse and human hemoglobin at 298 and 77 K four different Cu(II) binding sites were identified. The low affinity horse hemoglobin site with the sulfhydryl blocked (site 1) was found to be located 10-13 A from the sulfhydryl spin label on the surface of the molecule. Only with a free sulfhydryl is the site (site 2) in the pocket between the F and H helices closer to the SH-group and the iron populated. It is site 2 which is responsible for the oxidation. In frozen solutions a Cu-nitroxide distance of about 17 A was determined with human hemoglobin. This distance is consistent with the previously postulated location of the "high affinity" human hemoglobin site near the amino terminus of the beta-chain. At 298 K a much shorter Cu-nitroxide distance of about 7 A was calculated for human hemoglobin. This shorter distance at higher temperature also correlated with a slightly smaller value of g11 and A11 for the Cu(II) ESR spectrum. It is postulated that in solution cross-linking between nitrogenous ligands in the region of the amino terminus of one beta-chain and the carboxyl terminus of the other beta-chain can explain this shorter distance. This cross-link could involve histidine beta-143, which is one of the ligands thought to be also involved in site 1. Binding to the "high-affinity" site in solution thus stabilizes the "low-affinity" site 2 relative to site 1 explaining the reported interaction between the "high-affinity" and "low-affinity" sites.

Organotin-protein interactions. Binding of triethyltin bromide to cat haemoglobin.

Triethyltin binds to native cat and rat haemoglobin but not to their denatured forms or to other animal haemoglobins. Two molecules of the organotin bind to one molecule of R-state cat haemoglobin with affinity constants of about 1 X 10(5) M-1. Little or no triethyltin is bound to the deoxygenated (T-state) protein. Binding appears to be dependent upon the existence of a specific three-dimensional configuration of cysteine and histidine residues. The properties of the triethyltin-cat haemoglobin complex are consistent with those of a haemoglobin conformer whose allosteric equilibrium is displaced toward the R-state. Its oxygen affinity and rate of oxidation by nitrite is increased, and the rate of reduction of the methaemoglobin derivative by ascorbate is decreased. These effects of triethyltin are opposite and antagonistic to the effects of inositol hexaphosphate. They are exerted on the alpha- as well as beta-haem groups, even though triethyltin is bound at sites on alpha-globin far removed from the haem groups.

The effects of triethyltin bromide on red cell and brain cyclic AMP-dependent protein kinases.

Triethyltin bromide activates the cyclic AMP-dependent protein kinases of human red cell membranes and of bovine brain. Additions of 25-500 microM triethyltin to red cell ghosts resulted in enhanced phosphorylation of ghost proteins. When added to partially purified cyclic AMP-dependent protein kinases from red cell ghosts or bovine brain, stimulation of the phosphorylation of calf thymus histone was observed. The enhancement of kinase activity was due to release of catalytic subunits from the intact protein kinase. Brief exposure of the partially purified enzymes to triethyltin, followed by DE52 chromatography, resulted in elution profiles for regulatory and catalytic subunits that were similar to the profile resulting after cyclic AMP activation. Triethyltin interacts with both regulatory and catalytic subunits. When it was added to the partially purified cyclic AMP-dependent protein kinases from human red cell ghosts or bovine brain, noncompetitive inhibition of cyclic AMP binding to the regulatory subunit of the enzyme was observed. It interacted with the catalytic subunit to produce slow inhibition of catalytic activity. The inhibition was non-competitive with respect to both histone and ATP. When intact red cells were subjected to brief exposure with triethyltin, enhanced phosphorylation of certain membrane proteins occurred, suggesting that the activation of the cyclic AMP protein kinases by triethyltin may be physiologically significant.

Inactivation of yeast hexokinase B by triethyltin bromide.

Triethyltin bromide was found to demonstrate temperature-dependent inactivation of yeast hexokinase B. At temperatures of 20 degrees C or lower, little or no inactivation of the enzyme was detected after 2 h of reaction with 50-300 microM concentrations of the reagent. However, incubation at 25 degrees C or higher resulted in an increased rate and extent of loss of the enzyme activity with increasing incubation temperatures. The Arrhenius plot for the inactivation process showed a sharp break at approximately 30 degrees C, with a heat of activation (delta H*) above this temperature of 55.2 kcal, indicating that a triethyltin-induced conformational change occurred at the elevated temperatures. Sugar substrates provided protection against the inactivating effect by reducing the binding of triethyltin to the enzyme. In the absence of glucose, two sites of different affinity for triethyltin exist in the hexokinase monomer. Binding of triethyltin to the enzyme shifted its monomer-dimer equilibrium toward the monomeric form in an early stage of the interaction. Inactivation of the enzyme was associated with a slower subsequent event. Comparative effects of various organotin compounds on the activity of the enzyme indicated that inhibitory potency was associated with increasing hydrophobicity of the alkyl groups attached to the tin.

Inactivation of yeast hexokinase B by triethyltin bromide and reactivation by dithiothreitol and glucose.

Binding of triethyltin bromide to yeast hexokinase B results in a rapid change in the reactivity of the sulfhydryl groups of the molecule. The change was characterized by an increased rate as well as extent of reaction of the -SH groups, and it preceded the onset of inhibition of the enzyme. Rapid gel filtration of the enzyme-triethyltin complex reversed this change in sulfhydryl reactivity, and when the eluted enzyme was subjected to short incubation periods, the slow inhibition that occurs with the unfiltered enzyme-triethyltin complex was no longer manifested. With prolonged incubation, however, the gel-filtered sample demonstrated increased rate of loss of enzyme activity, indicating that the gel filtration step did not completely reverse the effects of triethyltin on the enzyme. Active enzyme was recovered, following the inactivation of yeast hexokinase with triethyltin, by incubation of the inactivated enzyme with a large excess of glucose and dithiothreitol. Near total recovery of enzyme activity with reversion to native enzyme conformation was achieved following incubation at 35 degrees C of the enzyme with glucose and dithiothreitol each at 0.1 M. The possible involvement of either cysteine or histidine in the binding of triethyltin to the enzyme was probed, and it was concluded that neither of these amino acids are donor ligands for tin.