Spin contribution to the thermodynamics of ligand binding to methemoglobins and metmyoglobins. I. Azide ion binding to horse-heart myoglobin.

The binding of azide ion to horse-heart myoglobins has been studied at pH 6.98 and at various temperatures. The results show that the azide complex is not completely loe spin and that the spin population is strongly dependent on temperature. We have shown that with some assumption it is possible to calculate the approximate fraction of high and low spin present at any temperature from the absorbance measurements. Corrections to the spin contribution at pH 6.98 to these values has been calculated.     

Response of myogenic and fibrogenic cells to cytochalasin B and to colcemid. I. Light microscope observations

Cytochalasin B (CB) induces a biphasic retraction is some cell types. The rapid response that peaks in 30 min leads to the "dendritic" condition. Replicating myogenic and fibrogenic cells, as well as postmitotic myoblasts and myotubes, participate in this reaction. This is followed by a slower phase that requires 40 h for stabilization and leads to the fully "absorized" state. Only replicating myogenic and fibrogenic cells participate in this reaction. Postmitotic myoblasts and myotubes do not arborize but round up and float off into the medium. Pretreatment with Colcemid does not block the rapid response to CB, but does block arborization. CB-arborized cells exposed to Colcemid while in the presence of CB develop sufficient tension to pull themselves apart. If CB depolymerizes actin-like filaments, and if such filaments constitute the only contractile system in the cell, then it is difficult to visualize how cells in CB develop such tension. Colcemid induces twisting, birefringent bands in interphase- and metaphase-arrested myogenic and fibrogenic cells, and in postmitotic myotubes. Such bands are more evident when CB-arborized cells are removed from CB and allowed to relax in Colcemid. These birefringent bands assemble in the prescence of cycloheximide, and may constitute 20% of the volume of the cell.     

Susceptibility of orbiviruses to low pH and to organic solvents.

Six orbiviruses, Corriparta, Wallal, Eubenangee, D'Aguilar, Warrego and Mitchell River, were inactivated within 30 min in solutions of pH less than 6. All but Wallal virus resisted treatment with ether at 1 degrees for 22 h but only Corriparta virus resisted treatment with chloroform at 1 degrees for 22 h. The genomes of the orbiviruses, including Corriparta virus, after electrophoresis in acrylamide gels separated into basically similar patterns which were distinct from the pattern of reovirus RNA.     

Stability of horse muscle acylphosphatase to heat and to urea.

The thermal stability of horse muscle acylphosphatase was investigated by measuring the inactivation constants at various pH and temperature values, and by differential spectra technique. This enzyme has high thermal stability in an acidic environment but is inactivated in an alkaline medium. It was found that the enzyme can be protected against such inactivation at pH 8.0 by increasing its concentration and the ionic strength of the solution. The effect of high urea concentrations on stability was also measured. It was found that spectral changes at 230 nm are related to urea inactivation of the enzyme, and that the enzymatic activity can be instantly and almost completely restored by dilution of the urea.