Effects of antimicrotubular agents in cAMP production and in steroidogenic response of isolated rat Leydig cells

In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time-dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8-Br-cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig cells.     

Decomposition of three halophytes in different habitats of an eastern scheldt salt marsh

Summary A 20.5-month study was undertaken to determine detrital processing of the halophytesSpartina anglica, Elytrigia pungens, andHalimione portulacoides in three different habitats of an estuarine salt marsh in the South-West Netherlands. Decomposition was measured using litter-bags of three different mesh sizes to partition the effects of different faunal groups on decomposition. From April 1980 through October 1981 litter-bags were sampled regulary from a creek, the upper marsh, and from a plant-debris belt on the higher marsh. Dry weights and nutritive values were measured and animals were counted. Mainly rates of loss are reported here. Zonal differences were significant. At first, decomposition in the creek was most rapid. After two months the processes in the creek slowed down because of the trapping of silt by the bags, which probably simulated the natural course of the decomposition process in the water. Decomposition on the marsh followed the most regular pattern, while in the plant-debris belt the pattern was very irregular. Population dynamics of microfaunal organisms supported these findings. In the plant-debris belts loss rates seem to be higher than on the marsh, because of the influence of detritivorous macrofaunal organisms. The loss rates of the three plant species differed significantly.Halimione decomposed fastest, especially in the beginning, and in the plant-debris habitat. On the upper marsh and in the plant-debris belt the loss rates ofSpartina seem to be a little higher than those ofElytrigia.Communication No. 233, Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

The role of histones H3 and H1 in the formation of thymine-lysine cross-links during UV-irradiation of deoxyribonucleoprotein

The effect of UV light (lambda = 254 nm) on calf thymus DNP at low ionic strengths was studied. It was found that at the irradiation doses used the protein in the DNA-protein complex increases as the irradiation dose rises. Thermal treatment and acid hydrolysis resulted in a predominant release of histones H3 and H1 from the complex. Data from liquid high performance chromatography, amino acid analysis, thin-layer chromatography point to the induction by UV-light of a thymine-lysine bond, whose formation involves DNA thymines and histone lysine residues, predominantly H3 and H1 fractions.     

Effect of serotonin on the yield of UV- and x ray-induced DNA damage

Using two-dimensional thin-layer chromatography, the effect of serotonin on the yield of thymine dimers and on cleavage of the N-glycosidic bond in the DNA irradiated with ultraviolet (UV) light and X-ray was studied. Bound serotonin was shown to reduce the synthesis of UV-induced thymine dimers but had no effect on the number of X-ray-induced breaks in the N-glycoside bonds in thymidine residues. The data obtained are discussed in terms of the mechanisms of serotonin involvement in the photoprotection of yeast cells from the lethal action of UV and X-ray irradiations.     

Soluble, prolonged-acting insulin derivatives. II. Degree of protraction and crystallizability of insulins substituted in positions A17, B8, B13, B27 and B30

It has previously been found that insulins, to which positive charge has been added by substitutions in position B30, thus raising the isoelectric point towards pH 7, had a prolonged action when injected as slightly acidic solutions because such derivatives crystallize very readily upon neutralization. Positive charge has now been added by substituting the B13 and A17 glutamic acid residues with glutamines and B27 threonine with lysine or arginine. These substitutions were introduced by site-specific mutagenesis in a gene coding for a single-chain insulin precursor. By tryptic transpeptidation the single-chain precursors were transformed to the double-chain insulin structure, concomitantly with incorporation of residue B30. Thus insulins combining B13 glutamine, A17 glutamine and B27 lysine or arginine with B30 threonine, threonine amide or lysine amide were synthesized. The time course of blood glucose lowering effect and the absorption were studied after subcutaneous injection in rabbits and pigs. The prolonged action of B30-substituted insulins was markedly enhanced by B27 lysine or arginine substitutions and by B13 glutamine. The B27 residue is located on the surface of the hexamer, so a basic residue in this position presumably promotes the packing of hexamers at neutral pH. The B13 residues cluster in the centre of the hexamer. When the electrostatic repulsive forces from six glutamic acid residues are abolished by substitution with glutamine, a stabilization of the hexamer can be envisaged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of ascorbic acid on the binding of 3H-GABA and 3H-glutamic acid to synaptosomes of the rat cerebral cortex

The effects of different concentrations of L-ascorbic acid (Asc) on Na+-dependent binding of 3H-GABA and 3H-DL-glutamic acid to rat brain cortical synaptosomes were studied. Asc, at a concentration nearly equal to brain extracellular one (3 X 10(-4) M), had no effect on specific and nonspecific 5H-GABA binding. At higher concentrations (10(-3) M) Asc strongly inhibited, and at lower concentrations (10(-6) M) considerably stimulated 3H-GABA binding. At a concentration of 10(-5)-10(-3) M Asc tended to decrease 3H-DL-glutamic acid binding.     

Range of the antigenic specificity of peptidoglycan in Staphylococcus aureus compared to other representatives of the Staphylococcus genus

In investigations based on the use of a highly sensitive test system permitting the detection of normal human antibodies to S. aureus peptidoglycan, the antigenic relationships between the peptidoglycans of S. aureus and other representatives of the genus Staphylococcus have been studied. Among other staphylococcal species, S. simulans, S. xylosus, S. hyicus, S. cohnii, S. hyicus s. s. chromogenes have been found to possess peptidoglycans most closely related to S. aureus peptidoglycans, while S. warneri and S. epidermidis peptidoglycans have proved to be least closely related to it.     

Mechanisms of induced processes in aqueous hemoglobin solutions at 77 K

ESR spectra of gamma-irradiated and frozen at 77 K human oxyhemoglobin and partially denaturated methemoglobin solutions were analysed. The quartet signal ascribed to the anion-radical of proximal histidine was shown to dominate in the spectra of both solutions. The spectra of methemoglobin solution irradiated with relatively small doses have an intensive singlet ascribed to the stabilized electron. The formation mechanism of free radicals is discussed.