Mg2+ restores membrane potential in rat liver mitochondria deenergized by Ca2+ and phosphate movements

Cellular ornithine biosynthesis could be expected to play a significant role in putrescine formation and hence in growth. Two enzymes are involved in ornithine biosynthesis: arginase and transamidinase. These enzyme activities were studied in two human melanoma cell lines differing in their K_m of diamine oxidase for putrescine and in their tumorigenicity in nude mice. Arginase activity accounts for the majority of ornithine formed in the highly tumorigenic cell line, while the majority of ornithine is derived from transamidinase action in the poorly tumorigenic cell line, with concomitant formation of methyl guanidine, a potent inhibitor of diamine oxidase.     

Glycinebetaine biosynthesis and its control in detached secondary leaves of spinach

In secondary leaves from spinach plants pretreated in vermiculite for 24 h with 300 mM NaCl, glycinebetaine accumulated at a rate of circa 0.16 mol 100 g^-1 Chl d^-1 (2 mol g^-1 FW d^-1), about three times the rate of control plants. The soluble carbohydrate and free amino acid contents did not increase significantly following salinisation until after 4 d when the relative growth rate also decreased. Leaf proline levels remained very low throughout the experimental period. K⁺ on a tissue water basis remained constant at 200 mM while Cl^- and Na⁺ levels increased linearly to reach 175 and 100 mM respectively after 5 d of saline treatment. The osmotic pressure of leaf tissue also increased from 300 to 500 mosmol kg^-1. These experimental conditions were considered suitable to study glycinebetaine biosynthesis and its induction by salinity in the absence of marked growth inhibition or metabolic disturbance. Radioactive labelled [¹⁴C]serine, ethanolamine and choline (all 1 mol, 13.3 MBq in 10 l) were fed to detached secondary leaves via the petiole 24 h after the exposure of plants to salt. The rate of isotope incorporation into water soluble products, lipids and residue was measured over a further 24 h. The major metabolic fate of exogenous [¹⁴C]choline and [¹⁴C]ethanolamine was incorporation into glycinebetaine while less ¹⁴C-label was found in phosphatidyl choline and phosphatidyl ethanolamine. Incorporation rates were identical in control and salinised leaves and were adequate to account for observed values of glycinebetaine accumulation previously reported in spinach. In contrast the labelling of glycinebetaine from [¹⁴C]serine was twice as great in salinated plants as in the controls. These results, together with short term labelling experiment with [¹⁴C]ethanolamine using leaf slices, were consistent with the formation of glycinebetaine via serine, ethanolamine and its methylated derivatives to choline with some control being exerted at the serine level. However a flux through the phosphorylated intermediates is not excluded.From a consideration of these results and the published data on barley subjected to water stress (Hanson and Scott, 1980 Plant Physiol. 66, 342–348) there appear to be significant differences in the biosynthetic pathways in spinach and barley.Abbreviations BHT butylated hydroxytoluerte (2,6-di-tert-butyl-4-methylphenol) - C₁ one-carbon fragment - 1,2DG diglyceride moiety - DW day weight - MCW methanol-chloroform-water (12:5:1, by vol.) - PA phosphatidic acid - PC phosphatidyl choline - PMME phosphatidyl monomethylethanolamine - PDME phosphatidyl dimethylethanolamine - PE phosphatidyl ethanolamine - PPO 2,5-diphenyloxazole - POPOP 1,4-bis(5-phenyloxazoyl) benzene     

Protein synthesis during the transition from the resting to the growing state in suspension cultures of Paul's Scarlet rose cells

Cells derived from Paul's Scarlet rose ( Rosa sp. ) were grown in the chemically defined medium of Nesius. When a stationary phase culture was diluted with fresh medium, growth was initiated after a pronounced lag period. DNA replication, as revealed by thymidine labeling and autoradiography, did not begin until 36 h, and mitotic figures were not observed until 48 h after dilution. A 10–15 fold increase in the rate of protein synthesis occurred during the lag period. This was brought about by a 3.5 fold increase in the amount of ribosomal RNA per cell, plus a doubling of both the percentage of ribosomes that are present as polyribosomes and the average number of ribosomes per polyribosome. The spectrum of polypeptides synthesized by these cells during the lag and early log periods of growth was examined. Polyribosomes were extracted from the cells at intervals preceding and accompanying the initiation of proliferative growth. The polyribosomes were translated in a wheat germ cell-free protein synthesizing system and the ³⁵S-methionine-labeled translation products were separated on polyacrylamide slab gels and by 2-dimensional gel electrophoresis. Comparatively few differences were observed between stationary phase, lag phase and log phase cells in terms of the spectrum of polypeptides synthesized in vitro. However, these various phases of the growth cycle could be characterized by a relatively high rate of synthesis of a few specific polypeptides. That is, while most proteins are synthesized throughout the growth cycle and even in non-growing cells at approximately the same relative rates, there are a few variable proteins whose synthesis marks a particular phase of the growth cycle.     

The effect of the osmotic potential and specific ion concentration of the nutrient solution on the uptake and reduction of nitrate by barley seedlings

Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψ^π) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized to (Ψ^π) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl₂ or Na₂SO₄. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO₃. The nutrient solutions were sampled for NO₃ analysis each day immediately before renewing the solutions. The accumulative loss of NO₃ from the solutions was considered to be uptake whereas NO₃ reduction was the difference between uptake and seedling content. Lowering the (Ψ^π) of the nutrient solutions resulted in decreased concentrations of NO₃ in the plant, little or no effect (except at the lowest (Ψ^π) level) on uptake, and increased nitrate reductase activity. Increased rates of NO₃ reduction were in particular associated with the Cl concentration of the nutrient solution.     

Tyrosine Hydroxylase Regulation: Apparent Kinetic Alterations Following Incubation of Brain Slices in a Sodium-free Medium

In an attempt to determine if alterations in intraneuronal Ca2+ may regulate tyrosine hydroxylase activity, brain slices were subjected to experimental manipulations known to increase the intraneuronal concentration of free Ca2+ ions. Incubation of either striatal or olfactory tubercle slices in a Na+-free medium for 15 min at 37 degrees resulted in a marked increase in the activity of tyrosine hydroxylase present in the 20,000 g supernatant fraction of homogenates prepared from the slices. Tyrosine hydroxylase isolated from slices previously incubated in a Na+-free, choline-enriched medium or in a Na+-free, sucrose-enriched medium exhibited maximal activities when assayed at pH 6.0 and 7.0, respectively. However, the percentage stimulation of enzyme activity induced by incubation of the slices in a Na+-free medium was maximal when the enzyme assays were performed at pH 7.0. The observed increase in enzyme activity seems to be mediated by a decrease in the apparent Km of the enzyme for pteridine cofactor, regardless of whether the kinetic enzyme analyses were conducted at pH 6.0 or 7.0, and by an increase in the Ki of the enzyme for end-product inhibitor dopamine. The apparent kinetic changes in the enzyme do not seem to result from alterations in the endogenous dopamine content of the slices, and they are independent of any increase in dopamine release that might have occurred as a response to the augmented intraneuronal Ca2+ concentration. Furthermore, the activation of tyrosine hydroxylase produced by incubating slices in a Na+-free medium is observed even in slices depleted of dopamine by pretreatment of rats with reserpine 90 min before preparation of brain slices. The activation of tyrosine hydroxylase observed under these experimental conditions does not seem to be mediated by cAMP or by a cAMP-dependent phosphorylation process. It is suggested that the changes in tyrosine hydroxylase reported are mediated primarily by a rise in the free Ca2+ concentration within the nerve tissue. These observations are consistent with the hypothesis that the kinetic activation of tyrosine hydroxylase produced after depolarization of central dopaminergic neurons may occur through a Ca2+-dependent even other than transmitter release.     

Mineral salt requirements of Bacillus globisporus subsp. marinus strains

The mineral salt requirements of four isolates of Bacillus globisporus subsp. marinus and of two terrestrial strains of B. globisporus were investigated. In contrast to the terrestrial reference strains the marine isolates showed an obligate requirement for sodium and potassium. The sodium ion could not be replaced by potassium or by osmotically equivalent concentrations of mannitol. None of the strains proved to be dependent upon Mg²⁺ or Ca²⁺. The B. globisporus subsp. marinus strains are considered true marine bacteria. The criteria used to distinguish between marine and terrestrial Gram-negative bacteria can also be applied for Gram-positive bacteria.     

Leishmania tropica: pathogenicity and in vitro macrophage function in strains of inbred mice.

Of seven strains of inbred mice and one hybrid that were infected intracutaneously with 5, 10, or 20 × 10⁶ active promastigotes of Leishmania tropica major, two strains (CBA/Ca and C₃H/He) recovered from the infection and their lesions healed within 3 to 5 months. The other strains, with the possible exception of C57B1/6 animals, remained infected, carrying large cutaneous ulcers throughout their lives. These included DBA/2, A/Jax, Balb/c, athymic nude mice of Balb/c origin (nu/nu) and the heterozygote Balb/c (nu⁺). The responses of C57B1/6 animals were of intermediate type with a tendency toward nonhealing at higher doses of the parasite. The cutaneous infection of athymic nude mice invariably gave rise to fulminating visceral infections and death. This condition was never observed in the other strains tested. Concanavalin A (Con A)-stimulated syngeneic or allogeneic lymphocytes of intact mice activated peritoneal macrophages of both healer and nonhealer mice, resulting in complete destruction of phagocytosed L. enriettii within 24 to 48 hr. The destruction of ingested L. tropica was confined to macrophages of healer mice and required 72 to 96 hr to reach completion. However, removal of Con A-stimulated lymphocytes from macrophage cultures and regular pulsing of the cells with a lymphokine-rich supernatant produced a state of sustained activation, resulting in destruction of L. tropica inside macrophages of both healer and nonhealer mice. The ability of Con A-stimulated lymphocytes of nonhealer animals to induce effective levels of activation in healer macrophages on one hand, and eventual destruction of L. tropica in macrophages of nonhealer mice under condition of sustained activation on the other, had indicated that so far as the in vitro situation is concerned, there is no inherent defect in lymphocytes or macrophages of nonhealer animals, although the threshold of activation necessary for killing of the parasite seems to be higher for cells of nonhealer origin.     

Schistosoma mansoni: thiol proteinase properties of adult worm "hemoglobinase".

This report presents evidence that the “hemoglobinase” from adult Schistosoma mansoni, first described by Timms and Bueding and later by Senft and his collaborators, belongs to the class of thiol proteinases. Proteolytic activity is stimulated by SH-containing compounds and inhibited by N-ethylmaleimide as well as other inhibitors of thiol proteinases. The enzyme can be partially purified by affinity chromatography using a Sepharose-linked organomercurial ligand. In addition to its activity on globin and hemoglobin, the enzyme can also be assayed with Azocoll, a general protease substrate, and by the activation of inactive trypsinogen to active trypsin. Extraction of the enzyme is enhanced by the addition of the nonionic detergent Triton X-100.     

Ultrastructure and ATPase activity of the rectal gland of the chondrichthyean fish Hydrolagus colliei (Holocephali)

Summary The anatomy, histology, ultrastructure and ATPase activity of the intramural rectal gland of the chondrichthyean Hydrolagus colliei, are described. The cells of the rectal gland of Hydrolagus demonstrate the same well developed lateral and basal cisternae, elongate mitochondria and luminal border as those of their elasmobranch counterparts. ATPase activity within the rectal gland of Hydrolagus is as intense as that in a number of elasmobranchs examined in the course of the study. Despite its primitive intramural location the rectal gland of Hydrolagus respresents a homolog of the more specialized and better known elasmobranch gland and appears as well suited for cation excretion.