Cadmium-substituted skeletal troponin C metal binding investigations and sequence assignment of the cadmium-113 resonances

The binding of cadmium to the calcium binding subunit of skeletal troponin (STnC) has been reinvestigated using direct binding methods and fluorescent derivatives. These data provide straightforward explanations of the observed titration behavior in the 113Cd NMR (Ellis, P.D., Strang, P., and Potter, J.D. (1984) J. Biol. Chem. 259, 10348-10356). Further, fluorescent derivatives of skeletal troponin C provide an excellent means of establishing a sequence assignment for the resonances observed in the 113Cd NMR. The results of these experiments demonstrate that sites I and II, the Ca2+ regulatory sites, can be assigned to resonances at -108.5 and -101.5 ppm, respectively. Sites III and IV, the structural sites, are assigned to resonances -112.8 and -106.8 ppm, respectively. These data are discussed in terms of recent structural findings and speculations.     

Renal excretion capacity in hydrated desert rodents (Jaculus orientalis andJaculus deserti)

Summary The capacity to excrete a water load was studied in rats and in two desert rodents (Jaculus orientalis andJaculus deserti) adapted to either 5 or 30°C ambient temperature. The rat is able to eliminate the entire water load regardless of thermal adaptation. Cold-adaptedJ. orientalis andJ. deserti excreted 60% of the water load in comparison to 20–30% in warm-adapted jerboas.At both adaptation temperatures, antidiuretic hormone (ADH) concentration was estimated at maximum diuresis in the two desert species. Though hydration induced a significant decrease in ADH concentration in both species, its level in the plasma remained relatively high. The decrease was more pronounced inJ. orientalis thanJ. deserti.Abbreviation ADH antidiuretic hormone     

Nuclear magnetic resonance investigation of cadmium 113 substituted pea and lentil lectins

The lentil (LcH) and pea (PSA) lectins, which are members of the class of D-glucose/D-mannose binding lectins, are Ca2+ X Mn2+ metalloproteins that require the metal ions for their saccharide binding and biological activities. We have prepared a variety of Cd2+ derivatives of PSA and LcH, with Cd2+ in either the transition metal (S1) or calcium (S2) sites, or in both. Thus, Cd2+ X Zn2+, Cd2+ X Mn2+, and Ca2+ X Cd2+ derivatives were prepared, in addition to the Cd2+ X Cd2+ derivatives which we have recently reported. This is the first report of stable mixed metal Cd2+ complexes of lectins. The physical and saccharide binding properties of the Cd2+ derivatives of both lectins were characterized by a variety of physiochemical techniques and found to be the same as those of the corresponding native proteins. 113Cd NMR spectra of mono- and disubstituted 113Cd2+ complexes of LcH and PSA were recorded and compared with 113Cd NMR data for concanavalin A (ConA) (Palmer, A.R., Bailey, D.B., Behnke, W.D., Cardin, A.D., Yang, P.P., and Ellis, P.D. (1980) Biochemistry 19, 5063-5070). The data for the PSA and LcH derivatives were found to be very similar, indicating close homology of their metal ion binding sites. 113Cd resonances at 44.6 ppm and -129.4 ppm for 113Cd2+ X 113Cd2+ X LcH, and at 46.6 and -130.4 for the corresponding PSA derivative, are chemical shifts very similar to those observed for 113Cd2+ X 113Cd2+ X ConA. Assignment of the resonances to the transition metal (S1) and calcium (S2) sites were unambiguous since the Ca2+ X 113Cd2+ and 113Cd2+ X Zn2+ derivatives of both lectins showed single resonances characteristic of the S1 and S2 sites, respectively. The results indicate that, unlike ConA, 113Cd2+ binds tightly to PSA and LcH. Binding of monosaccharide to both lectins induce small (2 ppm) upfield shifts in their S2 113Cd resonances, in contrast to the larger shift (8 ppm) observed in ConA. The 113Cd2+ X Mn2+ complexes of PSA and LcH fail to show a 113Cd resonance characteristic of these derivatives, which provides evidence for the close proximity of the metal ions in the two proteins. The present findings indicate that the coordinating ligand atoms to the metal ions at the S1 and S2 sites in LcH, PSA, and ConA are the same.     

A transient voltage-dependent outward current in cultured cerebellar granules

Granule cells were dissociated from rat cerebella with a procedure that yields a 98% pure cell population. Potassium currents in these cells were studied using the patch-clamp technique. Depolarizing pulses of 10 mV step and 100 ms duration from a holding potential of –80 mV elicited two different potassium outward currents: a transient, low-voltage activated component and a long lasting, high-voltage activated component. At +30 mV, the total current reached an amplitude of 2 nA (mean value of 15 experiments). The reversal potential of the transient current, estimated by measuring tail currents, was –77 mV, close to that predicted by the Nernst equation. The transient current was half inactivated with a holding potential of –78 mV and completely inactivated with –50 mV or more positive holding potentials. Finally, the current decay could be fitted by the sum of two exponentials with time constants of about 20 and 250 ms.     

Stereological and functional investigations on isolated adrenocortical cells: Zona fasciculata/reticularis cells of chronically ACTH-treated rats

Summary The morphology and function of isolated inner (zona fasciculata/reticularis) adrenocortical cells of rats pretreated with ACTH for 3, 6, 9 or 12 days were investigated. ACTH treatment induced a notable time-dependent enhancement in the steroidogenic capacity (corticosterone production) and growth of inner cells. The volumes of cells, mitochondrial compartment, membrane space [the cellular space occupied by smooth endoplasmic reticulum (SER) membranes] and lipid-droplet compartment, as well as the surface area of mitochondrial cristae and SER tubules, were increased in relation to the duration of ACTH pretreatment, and showed a highly significant positive linear correlation with both basal and stimulated corticosterone production. The acute exposure of isolated cells to ACTH provoked a striking lipid-droplet depletion, the extent of which was linearly and positively correlated with stimulated corticosterone secretion. The hypertrophy of the mitochondrial compartment and SER are interpreted as the morphological counterpart of the enhanced steroidogenic capacity of inner adrenocortical cells, inasmuch as the enzymes of steroid synthesis are located in these two organelles, and it is well known that chronic ACTH exposure stimulates the de novo synthesis of many of them in vivo. The rise in the number of lipid droplets, in which cholesterol is stored, is interpreted as being due to the fact that, under chronic ACTH treatment, the processes leading to cholesterol accumulation in adrenocortical cells (exogenous uptake and endogenous synthesis) exceed those of its utilization in basal steroid secretion. Cholesterol accumulated in lipid droplets as a reserve material may be rapidly utilized after acute ACTH exposure to meet the needs of the enhanced steroidogenic capacity of adrenocortical cells.     

Thymocytes express a mRNA that is identical to hypothalamic luteinizing hormone-releasing hormone mRNA

1. A luteinizing hormone-releasing hormone (LHRH)-like molecule produced by thymocytes is similar to hypothalamic LHRH in both bioactivity and antigenicity. 2. We determined whether this thymic LHRH is identical to or only homologous with hypothalamic LHRH by synthesizing and sequencing the cDNA of rat thymus LHRH. 3. The thymocyte and hypothalamic LHRH cDNAs are identical, indicating, that the amino acid sequences of LHRH produced in the hypothalamus and the immune system are also identical. 4. This is the first report showing conclusively that cell of the immune system transcribe the authentic mRNA for a hypothalamic releasing factor, LHRH.     

Costs to host defence and the persistence of parasitic cuckoos.

Raising genetically unrelated young is maladaptive, yet brood parasitism is widespread in birds. In several systems, hosts can evolve near-perfect defences against the parasite (discrimination and rejection of unlike eggs), making it difficult to understand how the parasite continues to exist. This study demonstrates costs to host defences (e.g. rejection of one's own eggs) such that once the parasite goes extinct on a particular host species, defence mechanisms are selectively disadvantageous. The consequent loss of host defences, and potential for re-exploitation of the host by the parasite, can explain the continued persistence of avian brood parasites. The results provide one general explanation for coexistence of parasites and their hosts.     

Capacitance--voltage relationship in phospholipid bilayers containing gangliosides

Changes in the position of the minimum of the parabolic capacitance-voltage curve allow the measurement of the amount of ganglioside present in artificial bilayers made with phosphatidylcholine-ganglioside mixtures and asymmetrically shielded with Ca2+. The screening effect of the ionic solution must be considered. With ganglioside/phospholipid molar ratios of up to 15%, all glycolipids can be found at the membrane surfaces.