Studies on the properties of fish hemoglobins. Kinetics of reaction with oxygen and carbon monoxide of the isolated hemoglobin components from trout (Salmo irideus)

Disruption of hemoglobin oxygen transport does not impact oxygen-dependent physiological processes in developing embryos of zebra fish (Danio rerio)

Embryonic hemoglobin circulated by the developing heart in the early vertebrate embryo is widely assumed (without substantiation) to perform the same vital role of O2 carriage that it does in fetuses and adults. In order to challenge this assumption, we measured highly O2-dependent physiological variables like O2 consumption, cardiac performance, and initial swim bladder filling in the presence and absence of functional hemoglobin in the embryos and early larvae of the zebra fish, Danio ( = Brachydanio) rerio. Functional ablation of hemoglobin by carbon monoxide or phenylhydrazine did not reduce whole-animal O2 consumption, which was approximately 85 to 90 mumol.g-1.h-1. Similarly, no differences in heart variables like ventricular pressure development or heart rate, which increased from 135 to 175 bpm between stages 36h and 96h (indicating developmental stages 36 and 96 hours after fertilization, respectively), were observed in these experiments. Initial opening of the swim bladder was not influenced in the presence of CO-occupied hemoglobin but was significantly impaired when the embryonic hemoglobin was chemically modified by incubation with phenylhydrazine. That aerobic processes continue without hemoglobin O2 transport indicates the adequacy in the embryo of simple O2 diffusion alone even in developmental stages with extensive convective blood circulation generated by the heart.

Cooperativity and allosteric regulation in non-mammalian vertebrate haemoglobins

1. This review illustrates the vast range of molecular functions expressed in non-mammalian vertebrate haemoglobins; with particular reference to the degree of aggregation of haemoglobin subunits and their interactions with allosteric effectors. 2. In at least the broadest sense, these properties suggest that haemoglobin function in non-mammalian vertebrates can be viewed against the evolutionary hierarchy of organisms rather than from a purely adaptive perspective.

Detection of the heme perturbations caused by the quaternary R----T transition in oxyhemoglobin trout IV by resonance Raman scattering

The depolarization ratio dispersion and the respective excitation profiles of two structural sensitive Raman lines of oxyhemoglobin-trout IV (1,375 and 1,638 cm-1) have been measured at pH-values between 6.5 and 8.5. They were analyzed by employing a fifth order time dependent perturbation theory to calculate the polarizability tensor. This provides information about the pH-dependence of parameters reflecting symmetry classified distortions of the prosthetic heme groups. In order to correlate these distortions with functional properties of the molecule the following protocol has been employed: (a) a titration model was formulated relating each conformation of the molecule to a distinct set of distortion parameters the incoherent superposition of which provides the respective distortion parameter obtained from our Raman data. (b) The thermodynamic constants determining the equilibrium between these molecular conformations (i.e., the quaternary T and R-states, the low affinity t and the high affinity r-states of the distinct subunits, the pK-values of the Root- and Bohr groups) were obtained from a set of O2-binding curves that were analyzed in terms of an allosteric model suggested by Herzfeld and Stanley 1974. J. Mol. Biol. 82:231. The application of this procedure yields excellent reproduction of the pH-dependent effective distortion parameters of both Raman lines investigated. Thus established correlation between hemoglobin function (O2-binding) and structure (asymmetric perturbation of the hemegroup) provides some interesting insights into the molecular basis of the allosteric Root effect.

Redox properties of components I and IV of trout hemoglobins: kinetic and potentiometric studies

Redox properties of component I and IV from trout hemoglobin (Salmo irideus) have been studied kinetically and at equilibrium. In the case of component I of trout hemoglobin, the mid-point potential (Eh) is pH independent below the acid-alkaline transition (pKa approximately equal to 8.6) and decreases at higher pH, following the deprotonation of the water molecule. Similarly to human hemoglobin, the mid-point potential of component IV of trout hemoglobin is pH-dependent, but the redox Bohr effect is extended to more acid pH. Moreover, the cooperativity of the redox equilibrium process is higher than in human hemoglobin. These features parallel the oxygen-binding properties of the same hemoglobin components from trout hemolysate. Differently from human hemoglobin, the oxidation kinetics of the two hemoglobins from trout by potassium ferricyanide show markedly biphasic progress curves with pH-independent second-order rate constants. This behavior suggests a different energy barrier for the interaction with ferricyanide in the two types of subunit of both Hb components from trout.

The Root effect

Considering the presently available data it is clear that the Root effect represents an exaggerated alkaline Bohr effect which occurs in the absence of a normal acid Bohr effect and is associated with a loss of oxygen binding capacity at low pH. Undoubtedly at the molecular level the presence of a Ser residue at position F9(94) beta in these haemoglobin is of primary importance. No Root effect haemoglobin has yet been identified which lacks this substitution. On the other hand however many haemoglobins are known which possess this Ser residue and at the same time lack a Root effect. Other factors arising from interactions at other sites in the haemoglobin molecule are obviously sufficient to negate the otherwise stabilizing effect of this critical Ser residue. The loss of cooperativity of Root effect systems as the pH is lowered is readily explained as due to stabilization of the low affinity T state to such a degree that the switch to the high affinity R state is suppressed even in the fully liganded molecule. The observation of Hill coefficients of less than unity requires that within the T state chain heterogeneity exists such that the alpha and beta chain haems demonstrate significantly different affinities for ligand. The physiological role of Root effect haemoglobins is demonstrably not inevitably linked to the swim bladder but more probably arose from the need to oxygenate the poorly vascularized retina of many fishes.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermodynamic characterization of the allosteric transition in trout hemoglobin

The pH induced spectral changes in the Soret region occurring in the carbomonoxy derivative of trout HbIV have been measured under carefully controlled conditions of temperature and organic phosphate concentration. Parallel experiments on the kinetics of carbon monoxide dissociation by NO replacement have been performed over the same pH range. Both sets of results agree satisfactorily with a thermodynamic scheme independently drawn on the basis of functional data previously analyzed within the framework of a two state allosteric model. Thus, the whole body of data strongly supports the idea that the spectral changes are themselves an indication of the pH induced structural transition, thereby reflecting the stabilization of the liganded T-state of the molecule at low pH. This allows us to definitely conclude that the functional changes induced in trout HbIV-CO by protons are associated with a red shift of the Soret absorption band.

A comparative approach to protein- and ligand-dependence of the Root effect for fish haemoglobins

Ligand-binding equilibria, kinetics and (13)C n.m.r. spectra of bound (13)CO, of the haemoglobins from two fishes that are very distant on the evolutionary scale, i.e. the fourth haemoglobin component from Salmo irideus and the single component from Osteoglossum bicirrhosum, were studied. The C-terminal sequence was also determined for the haemoglobin from Osteoglossum. The results show that (i) the C-terminal residues of both chains are not directly responsible for the characteristic heterotropic effect known as Root effect, since for both fish haemoglobins these residues are identical with those of human haemoglobins. (ii) In all haemoglobins characterized by the Root effect a dependence of the (13)CO n.m.r. resonances on pH is observed. However, the extent of the shift(s) depends on the particular protein, and is probably the result of a combination of both tertiary and quaternary conformational changes. (iii) Both haemoglobins from trout and Osteoglossum manifest a functional heterogeneity between the two types of chains in the tetramer, which increases with proton activity. For CO, the effect is very small for trout haemoglobin IV, and very marked for Osteoglossum haemoglobin; for O(2) strongly heterogeneous binding curves were obtained at approx. pH6.2 with both haemoglobins. (iv) Estimations of the relative values of the affinity constants for the alpha and beta chains in the tetramer were obtained for both haemoglobins from (13)CO n.m.r. spectra at low fractional saturation. On the basis of these findings the molecular mechanism underlying the Root effect is discussed.

Properties of trout hemoglobins reconstituted with unnatural hemes

Native globins isolated from trout hemoglobin compoents I and IV have been reconstituted with proto-, meso-, and deuteroheme, and the spectral and functional properties of the reconstituted hemoglobins have been investigated. Equilibrium and kinetic studies allow the following conclusions. (a) The properties of the proto-reconstituted hemoglobins are very similar, or indistinguishable, from those of the native Hb's I and IV. (B) The CO binding kinetics for both proteins were found to be consistent with the equilibrium data: the overall association rate constant increases (and the autocatalytic character of the reaction decreases) in the order proto, meso, deutero. (c) A marked pH dependence of both ligand affinity and cooperativity is maintained in the reconstituted Hb's IV: at pH 6 the fractional saturation with oxygen in air (Root effect) is lower for proto- than for meso- and deutero-Hb IV. The results obtained, including partial photodissociation experiments at different pH values, can be considered, to a first approximation, consistent with the basic features of a simple two-states model.

The kinetics and equilibria of squirrel-fish hemoglobin. A Root effect hemoglobin complicated by large subunit heterogeneity

The functional properties of squirrel-fish hemoglobin have been measured by studying ligand binding equilibria and kinetics. The results show that squirrel-fish hemoglobin has a Root effect with a corresponding stabilization of the low affinity state. The properties of this state are pH dependent even in the absence of cooperativity. The effect of ATP shifts the overall ligant affinity towards the low affinity state and is characteristic of the allosteric effect caused by organic phosphates. Under pH and ATP conditions favoring the low affinity conformational state, a 10-fold difference in the binding kinetics of carbon monoxide to the alpha and beta subunits is observed.

Kinetic properties and electron paramagnetic resonance spectra of the nitric oxide derivative of hemoglobin components of trout (Salmo irideus)

The binding of nitric oxide to hemoglobin components of trout (Salmo irideus), i.e., Hb trout I and Hb trout IV, has been studied by optical and electron paramagnetic resonance spectroscopy. Kinetic studies show that the Root effect in Hb trout IV is operative also for NO, since a large increase in the dissociation velocity constant (j(4)) is observed as the pH is decreased below 7. Moreover, the time course of the displacement of NO by CO is heterogeneous, suggesting that alpha and beta chains may have different j(4) values. Low-temperature X-band electron paramagnetic resonance spectra have been recorded with Hb trout I and IV saturated with NO at different pH values. The spectra of Hb trout IV are strongly pH-dependent. The high-pH form (pH 8.1) shows axial symmetry and no resolved hyperfine splitting, while the low-pH form is rhombic with a hyperfine splitting of 6.5 G in the g(z) region. The latter form reflects a more distorted site with a more significant delocalization of the unpaired electron on the proximal histidine; both features indicate a destabilization of the ligand binding at low pH. On the other hand, spectra of Hb trout I are axial at both pH values, with hyperfine splitting of 16.5 G, indicating that the site is not distorted and interacts with the ligand very strongly at either pH.