Dynamic structure of metallothionein

Molecular sieve chromatography of rabbit liver metallothionein at different electrolyte concentrations revealed that this protein undergoes an increase in Stokes radius from 1.50 to 1.78 nm when the ionic strength is lowered from 0.5 to 0.015 indicating a change in molecular shape and/or hydration. The variation in ionic strength also affects the far-UV circular dichroism of metallothionein reflecting a conformational transition in the protein. The effects are attributed to changes in intramolecular repulsion between the strongly negatively charged metal-thiolate clusters of the protein. It is suggested that metallothionein exists in at least two interchangeable conformational states which differ in hydrodynamic properties and whose equilibrium concentrations are determined by the electrostatic free energy of the system.     

The role ofH-2 regions in overcoming tissue incompatibility

Neonatal transplantation tolerance to the products of theH-2 ^b complex was induced in B10.A (H-2 ^a ) mice. On the basis of the survival of skin allografts it was found that antigens determined by theD region of theH-2 ^b complex (of the B10.A(2R) strain) were most easily overcome and that tolerance to the products of theD end of theH-2 complex (of the B10.A(4R) strain) was also easy to induce. The antigens produced by theK end ofH-2 (of the B10.A(5R) and B10.A(3R) strains) represented a stronger incompatibility barrier and a difference in the entireH-2 ^b complex caused strongest resistance to tolerance induction. When tolerance to the products of the entireH-2 ^b complex was induced in newborn B10.A mice, and the neonatally treated animals were grafted simultaneously with five different grafts, those disparate at theK end ofH-2 and in the entireH-2 region were rejected in some animals, while the grafts disparate at theD end of H-2 remained intact in the same mice. No dependence on theI-J subregion was observed in this system. Furthermore, tolerance was more easily inducible in male than in female B10.A mice.     

Evidence for interactions between the energy-dependent transport of sugars and the membrane potential in the yeastRhodotorula gracilis (Rhodosporidium toruloides)

Summary A membrane potential (inside negative) across the plasma membrane of the obligatory aerobic yeastRhodotorula gracilis is indicated by the intracellular accumulation of the lipid-soluble cations tetraphenylphosphonium and triphenylmethylphosphonium. The uptake of these ions is inhibited by anaerobic conditions, by uncouplers, by addition of diffusible ions, or by increase of the leakiness of the membrane caused by the polyene antibiotic nystatin. The membrane potential is strongly pH-dependent, its value increasing with decreasing extracellular proton concentration. Addition of transportable monosaccharides causes a depolarization of the electrical potential difference, indicating that the H⁺-sugar cotransport is electrogenic. The effect on the membrane potential is enhanced by increasing the sugar concentration. The half-saturation constants of depolarization ford-xylose andd-galactose were comparable to those of the corresponding transport system for the two sugars. All agents that depressed the membrane potential inhibited monosaccharide transport; hence the membrane potential provides energy for active sugar transport in this strain of yeast.     

Toronto scientists using wire mould to treat malignant melanomas of the choroid

The quadriceps tendon and patellar ligament rupture rarely, even when under great stress or trauma, but can rupture spontaneously in patients with chronic diseases such as gout, rheumatoid arthritis and renal disease. Several factors probably combine to weaken the tendon, including an impoverished local vascular supply, repeated microtrauma and secondary hypoparathyroidism with osteodystrophy. In the three cases reported here, one of which was bilateral, the patients were being treated for chronic renal disease; surgical repair of the tendons led to sound healing and a return to normal function of the joints.     

Microdetermination of monosaccharides in glycoproteins by gas-liquid chromatography

In a newly developed method for determining picomolar quantities of monosaccharides in glycoproteins, the methyl glycosides released by methanolysis of glycoproteins are separated as trifluoroacetates by gas-liquid chromatography and are detected with an electron capture detector. The application of the method has been demonstrated for the analysis of the carbohydrate moiety of secretory component isolated from human colostral immunoglobulin A.