Does a monospecific hybridoma always secrete homogeneous immunoglobulins?

The fusion of splenocytes (from mice immunized with the beta 2 subunit of E. coli tryptophan synthase) with myeloma cells which do not produce immunoglobulins gave rise to a clone secreting immunoglobulins with two distinct isotypes : gamma 1 and gamma 2b (Djavadi-Ohaniance et al. (1984) Biochemistry, 23, 97-104). Analysis of the immunoglobulins secreted by this clone indicates that these two isotypes are carried by two distinct heavy chains which are able to randomly associate to form hybrid molecules. In addition, two classes of light chains are able to randomly and to form heterologous associations with both the gamma 1 and gamma 2b heavy chains. Only the association between the gamma 2b heavy chains with one of the two classes of light chains leads to a combining site specific for the binding of the antigen beta 2.     

Regulation of Anterior Pituitary D2 Dopamine Receptors by Magnesium and Sodium Ions

At D2 3,4-dihydroxyphenylethylamine (dopamine) receptors in anterior pituitary tissue, magnesium ions shifted receptors to agonist high-affinity states, but decreased the affinity of the antagonist [3H]spiperone. Conversely, sodium ions shifted the receptors to agonist low-affinity states, but increased the affinity of [3H]spiperone. Magnesium is proposed to stabilize the hormone-receptor-guanine nucleotide regulatory protein complex, whereas sodium appears to destabilize this ternary complex. Thus, magnesium and sodium appear to mediate their regulatory effects via a common component at the D2 dopamine-receptor ternary complex.     

Self-association of sodium cholate in isotonic saline solutions

The self-association of dialyzed solutions of sodium cholate in isotonic saline solutions has been studied by vapor pressure osmometry and sedimentation equilibrium. These studies were carried out at 25, 31 and 37 degrees C. In all experiments the self-association could be described as a two-equilibrium constant, indefinite self-association in which odd species beyond monomer were absent. The plots of M1/Mna or M1/Mwa vs. c were quite smooth with no sharp breaks; this suggested that there were no critical phenomena. The temperature dependence of the self-association was quite small. Our results are in accord with other studies on sodium cholate which indicate that the self-association involves several species, and that it is not a monomer-n-mer self-association.     

Effects of experimental hypo-or hypernatremia on the fine structure of the pars intermedia of the murine pituitary

Summary Quantified ultrastructural observations of the pars intermedia (PI) of the murine hypophysis enable evaluation and kinetic study of relatively fine secretory changes in the gland. Changes in volume of rER and newly formed dense secretory granules (Golgi granules) appear to best translate functional variations in the PI, as shown by the morphological effects of drugs affecting the dopaminergic control of the gland. Our morphometric results show that the PI is stimulated, but only briefly (no longer than 8–12 days), by both salt-loading and Na deprivation. However, the PI displays different secretory patterns in salt-loaded and Na-deprived mice; moreover, bromocriptine, which abolishes PI stimulation in Na-deprived mice, has only a slight inhibitory effect in salt-treated animals. Thus, it appears that the stimulation of the PI under both experimental conditions is triggered by different mechanisms. These results underline the plurifactorial control of the PI and show that the gland may have complex effects on hydromineral regulation.     

Evidence that a 41,000 dalton brain phosphoprotein is pyruvate dehydrogenase

Phosphorylation of a brain protein of M_r=41,000, termed band F₂, is selectively regulated by effectors of pyruvate dehydrogenase kinase (pyruvate, dichloroacetate, NAD, NADH, CoA, and acetyl CoA). Subcellular fractionation studies indicate a mitochondrial localization of a phosphoprotein with this molecular weight. The phosphorylated α-subunit of purified bovine kidney pyruvate dehydrogenase comigrates with band F₂ on polyacrylamide gels and both appear as a doublet band of M_r=41,000?42,000. On the basis of similar regulatory properties, subcellular location and electrophoretic mobility, we propose that band F₂ is the α-subunit of the brain pyruvate dehydrogenase complex. Because band F₂ can be affected by physiological and behavioral treatments, our hypothesis suggests a potential regulatory role for pyruvate dehydrogenase in brain function.     

Ultrastructural Comparison of the Vacuolar and Mitochondrial H+-ATPases of Daucus carota

Eukaryotic vacuolar H⁺-ATPases (V-ATPases) are related to the F₀F₁-ATPases of chloroplasts and mitochondria and are believed to be organized into peripheral and integral membrane complexes. Vacuolar membranes isolated from purified carrot (Daucus carota) root vacuoles were observed to be coated with F₁-like particles after negative staining with phosphotungstic acid. The F₁-like particles formed typical “ball and stalk” structures, about 9.4 nm in diameter and 13.6 nm in height. The head portion frequently had a characteristic bifurcation or cleft at the apex and appeared to be composed of subunits. Such “V₁” complexes were frequently associated with smaller stalked particles emerging near the base. In contrast, negatively-stained carrot mitochondrial F₁ complexes averaged 8.7 nm in diameter and 11.7 nm in height. The head groups of the mitochondrial F₁s were nearly always spherical, and had no other smaller structures associated with them. The V₁ complexes of carrot are thus similar in form to the V₁ complexes of Neurospora (Bowman et al. J. Biol. Chem. 264 (1989) 15606–15612).