Effect of Acetate on Esterase C Activity During the Growth Cycle of Paramecium*

SYNOPSIS Enhanced esterase C activity could be demonstrated by starch gel electrophoresis in various stocks of Paramecium spp. (P. primaurelia stocks 90 and 540, P. biaurelia stock 93, P. tetraurelia stock 29. P. pentaurelia stock 87, P. octaurelia stocks 31 and 300, and P. multimicronucleatum species 3, stock 8 MO) grown in Adaptation Medium. This esterase, however, was barely detectable when they were cultivated in Axenic Medium. Addition of trypticase to Adaptation Medium resulted in reduction of esterase C in the ciliates. This effect is ascribable to Na acetate present in trypticase. Since esterase C increased with the decrease in acetate concentration (as estimated by gas-liquid chromatography) during growth of Paramecium, acetate appears to be utilized by the cells. Sensitivity of esterase C to acetate occurs in all 6 species of Paramecium examined. Different stocks within a species may have different levels of sensitivity; in one case this is genetically determined. The results emphasize the importance of controlling and manipulating growth conditions for the assessment of inter- and intraspecies variations in the isozymes of Paramecium.     

Oxygen inhibition of photosynthesis in the C4 species Amaranthus graecizans L.

In the C₄ plant, Amaranthus graecizans, increasing [O₂] from 2% up to 100% inhibited photosynthesis, quantum yield, and the carboxylation efficiency, and increased the CO₂ compensation point () from 2 to about 12 l/l. The O₂ inhibition of photosynthesis was fully reversible. When changing from 2.5 to 40% O₂ and vice versa, about 1 h was required for full equilibration with an O₂ inhibition of 18%; whereas in wheat, a C₃ species, inhibition of photosynthesis and its reversal occurs within minutes after changing [O₂], resulting in 63% inhibition of photosynthesis by 45% O₂. These differences in O₂ inhibition between a C₄ and C₃ species can be explained by high diffusive resistance across bundle-sheath cells of C₄ plants and the increased CO₂/O₂ ratio in bundle-sheath cells which is the consequence of the C₄ cycle. In A. graecizans, increased with increasing [O₂] but tended to reach a maximum at relatively high O₂ levels. The lack of a linear increase in as previously observed for C₃ species indicates that a considerable amount of photorespired CO₂ may be re-fixed with increasing levels of O₂. In comparison to previous reports with other C₄ species, photosynthesis of A. graecizans shows greater sensitivity to O₂, with a noticeable inhibition occurring with shifts from 2 to 21% O₂. A. graecizans has characteristics of other C₄ species with respect to Kranz anatomy, localization of PEP carboxylase in mesophyll cells and RuBP carboxylase in bundle-sheath cells, and little fractionation among carbon isotopes during CO₂ fixation. The basis for the higher sensitivity of photosynthesis of A. graecizans to O₂ may be based upon a lower diffusive resistance of gases across bundle-sheath cells than in some other C₄ species.Abbreviations CE carboxylation efficiency - RuBP ribulose-1,5-bisphosphate - CO₂ compensation point     

Selection and characterization of a feedback-insensitive tissue culture of maize

Tissue culture selection techniques were used to isolate a maize (Zea mays L.) variant D33, in which the aspartate family pathway was less sensitive to feedback inhibition by lysine. D33 was recovered by successively subculturing cultures originally derived from immature embryos on MS medium containing growth-inhibitory levels of lysine+threonine. The ability of D33 to grow vigorously on lysine+ threonine medium was retained after growth for 12 months on nonselection medium. New cultures initiated from shoot tissues of plants regenerated from D33 also were resistant to lysine+threonine inhibition. The K_i of aspartokinase for its feedback inhibitor, lysine, was about 9-fold higher in D33 than for the enzyme from unselected cultures. The free pools of lysine, threonine, isoleucine and methionine were increased 2–9-fold in D33 cultures. This was consistent with the observed change in feedback regulation of aspartokinase, the first enzyme common to the biosynthesis of these amino acids in the aspartate pathway. The accumulated evidence including the stability of resistance in the cultures, the resistance of cultures initiated from regenerated plants, the altered feedback regulation, and the increased free amino acids, indicates a mutational origin for these traits in line D33.Abbreviation LT lysine+threonine in equimolar concentration Paper No. 10880, Scientific Journal Series, Minnesota Agricultural Expertment Station     

Cytomorphogenetic- and anti-microtubule action of the antibiotic gougerotin inMicrasterias denticulata Bréb.

Summary Differentiating cells ofMicrasterias denticulata have been treated with aqueous solutions of the antibiotic gougerotin. Strong and characteristic cytomorphogenetic aberrations, resembling those of the anuclear type of development could be observed. It has been speculated that the aberrant growth of the growing half cell is the result of inhibition of protein synthesis by gougerotin.In addition to the morphogenetic influence, nuclear migration has been strongly inhibited by the drug. Therefore, it might be suggested that gougerotin is an active anti-microtubule agent.     

Spore and crystal formation inBacillus thuringiensis var.thuringiensis during growth in cystine and cysteine

The effect of the addition of different concentratons of cystine and cysteine on sporulation and parasporal crystal formation inBacillus thuringiensis var.thuringiensis was studied. The effect was well pronounced when the cystine/cysteine additions were made after the stationary phase. Heat stable spores and crystals were formed when the culture was provided with a low concentration of cystine/cysteine (0.05 per cent w/v). At a moderate concentration of cystine or cysteine (0.15%), only heat labile spores were formed without the production of the crystal. When the cystine/cysteine concentration was high (0.25%), spore and crystal formation were completely inhibited. Partial reversal of inhibition of sporulation was brought about by sodium sulphate or Zinc sulphate and lead, copper, cadmium or cobalt acetate at 0.2 mM or at 0.2% of sodium or potassium pyruvate, citrate, cisaconitate, oxalosuccinate, ∞ -keto-glutarate, succinate, fumarate, malate, or oxalacetate. Glutamate (0.2%) overcame the inhibitory effect of cystine/cysteine completely. The structural changes observed using phase contrast microscopy were dependent upon the concentration of cystine/cysteine.     

Hepatic and extra-hepatic glutathione-S-transferase activity in wild pigeons (Columba livia)

Glutathione-S-transferase (EC 2.5.1.18) activity was assayed in hepatic and extra-hepatic tissues of pigeons using l-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates. Gluthathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene in pigeon was in the order: kidney > liver > testes > brain > lung> heart. The enzyme activity with 1-chloro-2,4-dinitrobenzene as substrate was 40–44 times higher in pigeon liver and kidney than that observed with 1,2-dichloro-4-dinitrobenzene as substrate.K _m values of hepatic and renal glutathione transferase with l-chloro-2,4-dinitrobenzene as substrate were 2.5 and 3 mM respectively. Double reciprocal plots with varying reduced gluthathione concentrations resulted in biphasic curves with twoK _m values (liver 0.31 mM and 4mM; kidney 0.36 mM and 1.3 mM). The enzyme activity was inhibited by oxidized gluthathione in a dose-dependent pattern. 3-Methylcholanthrene elicited about 50% induction of hepatic glutathione transferase activity whereas phénobarbital was ineffective.     

Pentobarbital sodium inhibits calcium uptake in vascular smooth muscle

This report demonstrates that the commonly used anesthetic agent, pentobarbital sodium, in concentrations of 1 · 10^?4 to 2 · 10^?3 M inhibits calcium (Ca²⁺) uptake in both rat aortic and portal venous smooth muscle. The data indicate that total exchangeable Ca²⁺ in portal vein is reduced by about 15% in 1 · 10^?4 M pentobarbital sodium, while the intracellular exchangeable Ca²⁺ is reduced by 24%. On the other hand, in aortic smooth muscle, while 5–20 · 10^?4 M pentobarbital sodium reduces total exchangeable Ca²⁺ by about 15%, intracellular Ca²⁺ is reduced by 22% in 5 · 10^?4 M pentobarbital sodium and by 38% in 2 · 10^?3 M pentobarbital sodium. The present studies thus reveal that concentrations of pentobarbital sodium known to be present during induction of surgical anesthesia can exert significant inhibitory effects on exchangeability and transmembrane movement of Ca²⁺ in at least two different types of blood vessels.     

Vanadate inhibition of the Ca-ATPase from human red cell membranes

1. (1) VO₃⁻ combines with high affinity to the Ca²⁺-ATPase and fully inhibits Ca²⁺-ATPase and Ca²⁺-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca²⁺-dependent phosphoenzyme.

2. (2) VO₃⁻ blocks hydrolysis of ATP at the catalytic site. The sites for VO₃⁻ also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca²⁺-ATPase.

3. (3) The sites for VO₃⁻ show positive interactions in affinity with sites for Mg²⁺ and K⁺. This accounts for the dependence on Mg²⁺ and K⁺ of the inhibition by VO₃⁻. Although, with less effectiveness, Na⁺ substitutes for K⁺ whereas Li⁺ does not. The apparent affinities for Mg²⁺ and K⁺ for inhibition by VO₃⁻ seem to be less than those for activation of the Ca²⁺-ATPase.

4. (4) Inhibition by VO₃⁻ is independent of Ca²⁺ at concentrations up to 50 μM. Higher concentrations of Ca²⁺ lead to a progressive release of the inhibitory effect of VO₃⁻.

Inhibition of mineralization of urea nitrogen in soil

Summary The effects of anthraquinones and some other quinonoid and phenolic compounds on mineralization of urea N in soils were studied by estimating the influence on urease activity and nitrification. Anthraquinones did not affect the mineralization of urea N but 1,4-naphthoquinone; 2-methyl-1,4-naphthoquinone; 2–3-dichlorohydroquinone; 4,6-di-tert.butyl-o-benzoquinone; 4-tert.butylpyrocatechol and 4,6-di-tert.butylpyrocatechol inhibited urease activity and nitrification. The hydrolysis of urea (100 ppm) was not prevented by partial reduction in urease activity. The effective substances also inhibited dehydrogenase activity.