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B A Wittenberg

Publications and source records attributed to B A Wittenberg.

At least 55 records · Page 3Linked to original sources
PubMed1980

Uniform sarcomere shortening behavior in isolated cardiac muscle cells.

We have observed the dynamics of sarcomere shortening and the diffracting action of single, functionally intact, unattached cardiac muscle cells enzymatically isolated from the ventricular tissue of adult rats. Sarcomere length was measured either (a) continuously by a light diffraction method or (b) by direct inspection of the cell's striated image as recorded on videotape or by cinemicroscopy (120--400 frames/s). At physiological levels of added CaCl2 (0.5--2.0 mM), many cells were quiescent (i.e., they did not beat spontaneously) and contracted in response to electrical stimulation (less than or equal to 1.0-ms pulse width). Sarcomere length in the quiescent, unstimulated cells (1.93 +/- 0.10 [SD] micrometers), at peak shortening (1.57 +/- 0.13 micrometers, n = 49), and the maximum velocity of sarcomere shortening and relengthening were comparable to previous observations in intact heart muscle preparations. The dispersion of light diffracted by the cell remained narrow, and individual striations remained distinct and laterally well registered throughout the shortening-relengthening cycle. In contrast, appreciable nonuniformity and internal buckling were seen at sarcomere lengths < 1.8 micrometers when the resting cell, embedded in gelatin, was longitudinally compressed These results indicate (a) that shortening and relengthening is characterized by uniform activation between myofibrils within the cardiac cell and (b) that physiologically significant relengthening forces in living heart muscle originate at the level of the cell rather than in extracellular connections. First-order diffracted light intensity, extremely variable during sarcomere shortening, was always greatest during midrelaxation preceding the onset of a very slow and uniform phase of sarcomere relengthening.

Animals↗
PubMed1978

Myoglobin function in the isolated fluorocarbon-perfused dog heart.

An isolated dog heart preparation perfused with hemoglobin-free fluorocarbon suspension has been developed to study the role of myoglobin in myocardial function. The coronary vasculature was perfused at constant flow, with oxygen consumption determined from arteriovenous PO2 differences. Muscle function was assessed by measurement of pressures generated in a latex balloon placed in the left ventricle. The perfusate consisted of 20% perfluorotributylamine and 80% Ringer's lactate with 16 mM glucose. Steady-state oxygen consumption decreased from 0.30 to 0.11 ml/min per gram dry weight left ventricle, as perfusate PO2 decreased from 690 to 150 mmHg. Left ventricular pressure generation and oxygen consumption were determined before and after addition of 8 mM sodium nitrite, which changed functional ferrous myoglobin to high-spin ferric myoglobin. Over the range of perfusate PO2 studied, nitrite addition did not alter mechanical performance or myocardial oxygen consumption. These data suggest that those conditions necessary for substantial myoglobin-facilitated diffusion of oxygen in the myocardium are not present in the isolated fluorocarbon-perfused dog heart.

Animals↗
PubMed1976

Leghemoglobin. An electron paramagnetic resonance and optical spectral study of the free protein and its complexes with nicotinate and acetate.

Electron paramagnetic resonance (EPR) and optical spectra are used as probes of the heme and its ligands in ferric and ferrous leghemoglobin. The proximal ligand to the heme iron atom of ferric soybean leghemoglobin is identified as imidazole by comparison of the EPR of leghemoglobin hydroxide, azide, and cyanide with the corresponding derivatives of human hemoglobin. Optical spectra show that ferric soybean leghemoglobin near room temperature is almost entirely in the high spin state. At 77 K the optical spectrum is that of a low spin compound, while at 1.6 K the EPR is that of a low spin form resembling bis-imidazole heme. Acetate binds to ferric leghemoglobin to form a high spin complex as judged from the optical spectrum. The EPR of this complex is that of high spin ferric heme in a nearly axial environment. The complexes of ferrous leghemoglobin with substituted pyridines exhibit optical absorption maxima near 685 nm, whose absorption maxima and extinctions are strongly dependent on the nature of the substitutents of the pyridine ring; electron withdrawing groups on the pyridine ring shift the absorption maxima to lower energy. A crystal field analysis of the EPR of nicotinate derivatives of ferric leghemoblobin demonstrates that the pyridine nitrogen is also bound to the heme iron in the ferric state. These findings lead us to picture leghemoglobin as a somewhat flexible molecule in which the transition region between the E and F helices may act as a hinge, opening a small amount at higher temperature to a stable configuration in which the protein is high spin and can accommodate exogenous ligand molecules and closing at low temperature to a second stable configuration in which the protein is low spin and in which close approach of the E helix permits the distal histidine to become the principal sixth ligand.

Acetates↗
PubMed1975

Role of myoglobin in the oxygen supply to red skeletal muscle.

The contribution of nyoglobin to the oxygen uptake of red skeletal muscle was estimated from the difference in oxygen uptake with and without functional myoglobin. The oxygen uptake of bundles (25 mm long, 0.5 mm mean diameter) of muscle fibers teased from pigeon breast muscle was measured in families of steady states of oxygen pressure from 0 to 250 mm Hg. The oxygen-binding function of myoglobin, in situ in muscle fiber bundles, was abolished by treatment with nitrite of hydroxylamine, which convert oxymyoglobin in situ to high spin ferric myoglobin, or with phenylhydrazine, which converts oxymyoglobin to denatured products, or with 2-hydroxyethylhydrazine, which appears to remove myoglobin from the muslce. The oxygen uptake was again measured. At higher oxygen pressure, where oxygen availability does not limit the respiration of the fiber bundles, oxygen uptake is not affected by any of the four reagents, which is evidence that mitochondrial oxygen uptake is not impaired. At lower oxygen pressure, where oxygen uptake is one-half maximal, the steady state oxygen consumption is roughly halved by abolishing functional myoglobin. Under the steady state conditions studied, the storage function of myoglobin, being static, vanishes and the transport function stands revealed. We conclude from these experiments that myoglobin may transport a significant fraction of the oxygen consumed by muscle mitochondria.

Animals↗
PubMed1973

Nicotinic Acid as a ligand affecting leghemoglobin structure and oxygen reactivity.

A small molecule, hitherto called X, which is present in legume root nodules and ligates reversibly to the monomeric protein, leghemoglobin, with formation of a hemochrome structure, is identified as nicotinic acid. The binding constants at pH 5.3 are K = 7.3 x 10(5) M(-1) and K = 3.0 x 10(4) M(-1) for combination of nicotinic acid with ferric and ferrous leghemoglobin, respectively. This high affinity binding of ligand requires an unsubstituted pyridine ring nitrogen atom and an ionized carboxyl group in the 3-position of the ring. Binding of nicotinic acid is favored at acid pH and is reflected by diminished apparent affinity of leghemoglobin for oxygen.

Journal Article↗
PubMed1970

On the state of the iron and the nature of the ligand in oxyhemoglobin.

The structure of the oxygenated heme group of oxyhemoglobin may be formulated as [Hb(Heme d(1/2) (5)).OO(-)]. The heme iron atom is formally ferric, and the ligand is bound superoxide anion. When deoxyhemoglobin combines reversibly with oxygen a partial transfer of an electron occurs from the ferrous iron atom to the oxygen molecule. By surrendering its electron the iron atom has become ferric; in accepting an electron the ligated oxygen molecule has become a new species, the bound superoxide anion (.OO(-)). The configuration of the heme iron atom is deduced from comparison of the optical spectrum in the visible region of oxyhemoglobin with that of alkaline ferric hemoglobin whose configuration is established by electron paramagnetic resonance spectroscopy. The configuration of both species is low spin ferric heme iron (Heme d(1/2) (5)). The configuration of the ligated oxygen molecule of oxyhemoglobin is not accessible to study by magnetic or optical probes. However it may be known by analogy with the configuration of the ligated oxygen molecule of reversibly oxygenated cobalt complexes whose structure has been proved by both electron paramagnetic resonance and x-ray diffraction analysis. It is bound superoxide anion (.OO(-)). Other physical studies bearing on the structure of the oxygenated heme group are discussed. Reasons are given for believing that the proposed formulation of the oxyhemoglobin structure is consistent with the known stability of oxyhemoglobin.

Arteries↗
PubMed1969

Hemoglobin A: an electron paramagnetic resonance study of the effects of interchain contacts on the heme symmetry of high-spin and low-spin derivatives of ferric alpha chains.

Hemoglobin, the oxygen-binding heme protein of blood is composed of four subunits of two types, alpha and beta. Although the protein when isolated is diamagnetic, by oxidation it can be converted to various paramagnetic ferric forms exhibiting specific electron paramagnetic resonance (EPR) spectra. Using electron paramagnetic resonance, we have shown that the symmetry of the heme of isolated ferric alpha chains is different from that of the heme of these same subunits when associated with ferric beta chains in the parent tetramer. The high-spin form of the isolated ferric alpha chains shows a clearly resolved departure from tetragonal symmetry in contrast to ferrihemoglobin A, where the environment of the iron of all four chains is nearly tetragonal. This difference in heme symmetry suggests that the maintenance of tetragonal symmetry in the hemoglobin tetramer must be brought about by the configuration the alpha chains assume due to their contact with the beta chains. When isolated from the tetramer, some parts of the alpha chain must undergo physical displacement from a configuration that had been stabilized by the beta chains.Although differences in symmetry between monomer and tetramer are seen with high-spin forms, no such difference exists with two low-spin ferric forms. Here the symmetries of iron are primarily governed by the immediate ligand environment of the iron and not by the state of association of the protein.

Electron Spin Resonance Spectroscopy↗