Diferric transferrin reduction stimulates the Na+/H+ antiport of HeLa cells

Proton release from HeLa cells is stimulated by external oxidants for the transplasmalemma electron transport enzymes. These oxidants, such as ferricyanide and diferric transferrin, also stimulate cell growth. We now present evidence that proton release associated with the reduction of ferricyanide and diferric transferrin is through the Na+/H+ antiport. The stoichiometry of H+/e- release with diferric transferrin is over 50 to 1, which is greater than expected for oxidation of a protonated transmembrane electron carrier. Diferric transferrin induced proton release depends on external sodium and is inhibited by amiloride. Proton release is also inhibited when diferric transferrin reduction is inhibited by apotransferrin. A tightly coupled association between the redox system and the antiport is shown by sodium dependence and amiloride inhibition of diferric transferrin reduction. The results indicate a new role for ferric transferrin in growth stimulation by activation of the sodium-proton antiport.

Effect of (D-Trp6, Pro9-NEt)-GnRH on the function and ultrastructure of pituitary and testis in male rats

Groups of ten adult male Wistar rats were treated chronically with GnRH agonist for different durations. The responses of pituitary and testis to GnRH agonist were evaluated by serum and testicular testosterone, serum and pituitary LH, and testicular LH receptors. Testicular testosterone and LH receptors were decreased very significantly under our experimental regimen, irrespective of the duration of the treatment Serum testosterone levels were reduced after 10 and 15 injections, but only rats receiving 10 injections showed a significant increase in serum LH levels and decrease of pituitary LH content. The type II gonadotropes of the pars distalis of pituitary were increased in number but showed a higher degree of dilated smooth endoplasmic reticulum with few secretory granules. Many large lipid droplets appeared in the cytoplasms of the Leydig cells. Degenerative changes were observed in most seminiferous tubules following GnRH agonist treatment. Obvious abnormal acrosome and nuclear caps of some spermatids were also observed. The functional changes caused by GnRH agonist coincided with their ultrastructural appearance.

Determination of rate constants for the irreversible inhibition of acetylcholine esterase by continuously monitoring the substrate reaction in the presence of the inhibitor

The kinetics of the irreversible inhibition of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) by diisopropyl fluorophosphate and paraoxon have been studied by the approach of following the substrate reaction continuously in the presence of both the substrate and the inhibitor based on kinetic equations previously derived (Tsou, C.-L. (1965) Acta Biochim. Biophys. Sinica 5, 387-417). From determinations of the effects of different concentrations of substrate and the inhibitors on the apparent rate constants for the irreversible inhibition reactions it can be shown that these inhibitors are of the competitive complexing type. Both the reversible dissociation constant for the enzyme inhibitor complex and the rate constant for the subsequent phosphorylation step can be obtained from suitable plots of the experimental data.

Chloride secretory mechanism induced by prostaglandin E1 in a colonic epithelial cell line

Confluent T84 monolayers grown on permeable supports and mounted in a modified Ussing chamber secrete chloride (Cl-) in response to prostaglandin E1. The threshold stimulation was observed at 10(-9) M and a maximal effect at 10(-6) M. Unidirectional flux studies showed an increase in both serosal to mucosal and mucosal to serosal Cl- fluxes with 10(-6) M prostaglandin E1; the increase in serosal to mucosal Cl- flux exceeded the increase in mucosal to serosal flux, resulting in net Cl- secretion. Na+ transport was not affected in either direction and the changes in net Cl- flux correlated well with the changes in short circuit current. To identify the electrolyte transport pathways involved in the Cl- secretory process, the effect of prostaglandin E1 on ion fluxes was tested in the presence of putative inhibitors. Bumetanide was used as an inhibitor for the basolaterally localized Na+,K+,Cl- cotransport system whose existence and bumetanide sensitivity have been verified in earlier studies (Dharmsathaphorn et al. 1984. J. Clin. Invest. 75:462-471). Barium was used as an inhibitor for the K+ efflux pathway on the basolateral membrane whose existence and barium sensitivity were demonstrated in this study by preloading the monolayers with 86Rb+ (as a tracer for K+) and simultaneously measuring 86Rb+ efflux into both serosal and mucosal reservoirs. Both bumetanide and barium inhibited the net chloride secretion induced by prostaglandin E1 suggesting the involvement of the Na+,K+,Cl- cotransport and a K+ efflux pathways on the basolateral membrane in the Cl- secretory process. The activation of another Cl- transport pathway on the apical membrane by prostaglandin E1 was suggested by Cl- uptake studies. Our findings indicate that the prostaglandin E1-stimulated Cl- secretion, which is associated with an increase in cyclic AMP level, intimately involves (a) a bumetanide-sensitive Na+,K+,Cl- cotransport pathway that serves as a Cl- uptake step across the basolateral membrane, (b) the stimulation of a barium-sensitive K+ efflux mechanism on the basolateral membrane that most likely acts to recycle K+, and (c) the activation of a Cl- transport pathway on the apical membrane that serves as a Cl- exit pathway.

Reactivation kinetics of diethylphosphoryl acetylcholine esterase

The kinetics of reactivation of diethylphosphorylated acetylcholine esterase by pyridine-2-aldoxime methochloride has been studied using the approach of following the course of the hydrolysis of acetylcholine during the reactivation of the phosphorylated enzyme by the reactivator [Tsou, C.-L. (1965) Acta Biochem. Biophys. Sin. 5, 398-417]. Equations are derived based on the scheme of the formation of a complex between the phosphorylated enzyme and the reactivator and the rate of dissociation of this complex is not necessarily faster than the dephosphorylation and regeneration of the active enzyme. The regenerated enzyme then reacts with the substrate through an acetyl-enzyme intermediate as generally depicted. The equation obtained for product formation during the course of reactivation contains two exponential terms and this is in accord with the experimentally observed biphasic reaction. By making the assumption that the dissociation of the phosphorylated enzyme-reactivator complex is much faster than the dephosphorylation reaction, the above equation can be simplified to a form containing only one exponential term. By following the course of the reactivation reaction with the conventional approach of taking aliquots and assaying for enzyme activity recovery, it would appear likely that one would miss the initial stage of this biphasic reaction.

Alternative conformational states in the ribosome-associated 5.8S RNA

Two conformations of the 5.8S rRNA have been distinguished by gel electrophoresis. Diethyl pyrocarbonate and dimethyl sulphate reactivity were used to probe these conformational states in both the free molecule and those associated with 28S RNA or the ribosome. Both conformations could be demonstrated in each case and in every instance four residues, C50, A52, G53, C54, which were strongly reactive in the faster-migrating conformation were essentially unreactive in the slower-migrating form. These results suggest that the two conformations differ in the degree to which the tertiary structure is folded and raise the possibility that the 5.8S rRNA functions in translation by switching between alternative conformational states.

Structure of the ribosome-associated 5.8 S ribosomal RNA

The structure of the 5.8 S ribosomal RNA in rat liver ribosomes was probed by comparing dimethyl sulfate-reactive sites in whole ribosomes, 60 S subunits, the 5.8 S-28 S rRNA complex and the free 5.8 S rRNA under conditions of salt and temperature that permit protein synthesis in vitro. Differences in reactive sites between the free and both the 28 S rRNA and 60 S subunit-associated 5.8 S rRNA show that significant conformational changes occur when the molecule interacts with its cognate 28 S rRNA and as the complex is further integrated into the ribosomal structure. These results indicate that, as previously suggested by phylogenetic comparisons of the secondary structure, only the "G + C-rich" stem may remain unaltered and a universal structure is probably present only in the whole ribosome or 60 S subunit. Further comparisons with the ribosome-associated molecule indicate that while the 5.8 S rRNA may be partly localized in the ribosomal interface, four cytidylic acid residues, C56, C100, C127 and C128, remain reactive even in whole ribosomes. In contrast, the cytidylic acid residues in the 5 S rRNA are not accessible in either the 60 S subunit or the intact ribosome. The nature of the structural rearrangements and potential sites of interaction with the 28 S rRNA and ribosomal proteins are discussed.

Multiple-locus departures from panmictic equilibrium within and between village gene pools of Amerindian tribes at different stages of agglomeration

A comparative analysis of departures from multiple-locus Hardy-Weinberg equilibrium is presented for a set of four tribal Indian groups (the Yanomama, Makiritare, Wapishana and Ticuna) from the lowlands of South America. These tribes span a range of agglomeration and acculturation from the most traditional, swidden horticulturalists to frontier townspeople. The small-group social organization typical of traditional horticulturalists leads to substantial departures from tribal panmixia, as manifested by the distribution of multiple-locus genotypes both within and between villages. Within villages, the departures from single-locus Hardy-Weinberg equilibrium are small and nonsignificant, but the departures from gametic equilibrium (independence of loci) are substantial, even for the unlinked loci we have used to characterize these populations. The departures from single-locus homogeneity across villages are also substantial. One of the normal concomitants of increasing acculturation in this setting is an increase in agglomeration. As agglomeration increases, the departures from multiple-locus panmixia decrease, a process that can be very rapid. We discuss both the shifting balance theory of evolution and punctuated evolutionary rates in light of the small group social organization that must have obtained throughout most of human evolution.

Serum proteins in healthy Basenjis and Basenjis with chronic diarrhea

A serologic survey was conducted to characterize the electrophoretic patterns of serum proteins in healthy Basenji dogs (n = 137) and Basenjis with chronic diarrhea (n = 32). Serum protein electrophoresis values for Basenjis were similar to previously reported values from dogs of other breeds. Dogs with histologically confirmed lymphocytic-plasmacytic enteritis had a statistically significant (P less than 0.05) decrease in total protein, albumin, and albumin/globulin ratio. alpha 2-Globulin and gamma-globulin values were significantly increased in old dogs (9 years of age or older) with lymphocytic-plasmacytic enteritis. Although not statistically significant, gamma-globulin values were generally increased in Basenjis with lymphocytic-plasmacytic enteritis when compared with the values in age-matched clinically healthy Basenjis.

Effect of localized trauma and temporary splinting on immature skeletal muscle and mobility of the femorotibial joint in the dog

The right pelvic limbs of 2 groups of dogs were splinted in extension for 2 weeks. In 1 of these groups, the dogs were anesthetized and the distal portion of the quadriceps femoris muscle was traumatized before splinting. Two groups of control dogs were also used; neither group was splinted, but 1 group was anesthetized, and their muscles were traumatized. The range of motion of the femorotibial joint was measured in all 4 groups before splinting and 3 and 9 weeks after splinting. Types I and II muscle fiber diameters and percentages were also recorded at 3 and 9 weeks in all groups. Flexion of the femorotibial joint was limited after splinting (P less than 0.001), but less so after trauma and splinting than after splinting alone (P less than 0.0001). A reversible type I fiber atrophy occurred in most restricted muscles (P less than 0.001) and early type II fiber atrophy was seen in a few muscles after trauma and splinting (P less than 0.002). Multifocal fiber necrosis was the only irreversible change seen after 3 weeks of splinting with or without concurrent muscle trauma. Relative fiber percentages did not change appreciably during splinting or recovery.