Conversion of Tyrosine Hydroxylase to Stable and Inactive Form by the End Products

We have reported previously that tyrosine hydroxylase in the crude extract from rat striatum exists in the inactive form showing almost no activity at the physiological pH and that the inactive form is produced by the action of the end products of the enzyme, such as dopamine. The incubation of the enzyme with the end products resulted in not only the inactivation but also a remarkable stabilization of the enzyme. Catechols possessing amino groups but no negatively charged groups on the side chains (catecholamine-type catechols) were effective at a concentration as low as 10(-7) M in both the inactivation and stabilization of the enzyme. In contrast, catechols not possessing positively or negatively charged side chains (3,4-dihydroxyphenylethyleneglycol-type catechols) were ineffective at a concentration of 10(-7) M but effective at a concentration of 10(-6) M for both the inactivation and stabilization. Catechols possessing negatively charged groups (3,4-dihydroxyphenylacetic acid-type catechols) were ineffective even at a concentration of 10(-6) M. Thus, the end products of tyrosine hydroxylase appear to serve to keep the enzyme inactive and stable. The reaction mechanism of the conversion of the enzyme from the active/labile form to the inactive/stable form by dopamine was also investigated.     

发展生态渔业,保护水域环境——朱湖水体生态农业初探

渔业是大农业的一环。在充分合理的利用好水体自然资源,大力发展水产品生产的同时,认真保护好水域生态环境,这不仅是渔业的问题,也完全符合环保这项基本国策。研究渔业生态,发展生态渔业也是当今水产养殖发展的主要方向。“水体生态农业”是依据生态学原理,生态     

Correlations between chironomid pupal skin collections and habitats recorded from a chalk river

Chironomid pupal skins were collected during one year from three sites along a chalk stream in southern England. The sites had similar chemistry and discharge but differed in their current and temperature regimes. Substrate composition upstream of each collection point was surveyed during spring, summer and autumn. Proportions of macrophytes and sediments were compared with proportions of chironomid species and trophic groups. Seasonal changes in substrate and pupal skin collections were correlated by classification and direct ordination techniques. The distribution of chironomid species were indicated as being significantly related to the recorded substrate data.     

Measurement of chronic toxicity using the opossum shrimpMysidopsis bahia

The chronic toxicity of silver and endosulfan to the opossum shrimpMysidopsis bahia was determined using continuous-flow bioassays. The 28-day bioassays measured survival, fecundity, and growth (length and weight measurements). Maximum acceptable toxicant concentrations (MATC) were estimated from measured toxicant concentrations. MATC values were similar using either brood size or growth as a criterion for sublethal effects. As an alternative to the determination of fecundity impairment, measurement of growth reduction in response to exposure to toxicants may provide a useful tool in the assessment of chronic toxicity inMysidopsis life-cycle bioassays.     

The discovery of Myriophyllum exalbescens Fernald (Haloragaceae) in Europe and the typification of M.spicatum L. And M.verticillatum L.

Myriophyllum exalbescens Fernald, hitherto regarded as a North American endemic, has been fund to occur widely as a native plant in northern Europe, where it has occasionally been distinguished as a subspecies or variety of M.spicatum L.under the epithet squamosum Linnacus original concept of M.spicalum appears to have included M.exalbescens (and also M. Alterniflorum DC.) but selection of Burser VII(1)79 at UPS as lectotvpe ensures the continued use of the epithet spicatum for the native Eurasian weed species to which it is customarily applied. .M.verlicillalum L., the name of a morphologically similar species, is also lectotypified in a way that preserves its current usage. Distinguishing features of M.exalbescens and M.spicatum are provided along with details of the synonymy and presently known distribution in Europe of M.exalbescens .     

Absorption of gamma-emitting fission products and activation products by rice under flooded and unflooded conditions from two tropical soils

Summary The absorption of gamma-emitting fission products¹⁰⁶Ru,¹²⁵Sb,¹³⁷Cs and¹⁴⁴Ce and activation products⁵⁹Fe,⁵⁸Co.⁵⁴Mn and⁶⁵Zn by rice plants grown on two contrasting tropical soils, namely, a blak soil (pellustert) and a laterite (oxisol), and the effects of flooding were studied under controlled conditions. Results indicated greater uptake of¹⁰⁶Ru and¹²⁵Sb from the black soil than from the laterite. In contrast, the uptake of¹⁴⁴Ce and¹³⁷Cs was greater in the laterite than in the black soil. Flooding treatment enhanced the uptake of all these fission products by rice plants in the laterite soil whereas this effect was observed only for¹²⁵Sb and¹³⁷Cs in the black soil.The plant uptake of activation products from the two soil types showed maximum accumulation of⁶⁵Zn followed by⁵⁴Mn,⁵⁹Fe and⁵⁸Co in both soil types. Besides, uptake of these nuclides was greater from the laterite soil than from the black soil. Flooding treatment for rice while showing a reduction of⁵⁹Fe uptake, showed an increase in plant uptake of⁵⁸Co,⁵⁴Mn and⁶⁵Zn in both soil types.     

The mechanism of bicarbonate assimilation by the polar leaves of Potamogeton and Elodea. CO2 concentrations at the leaf surface

Abstract. Photosynthetic utilization of HCO, in leaves of Poiamogeton and Elodea occurs at the lower leaf side, with subsequent OH∼ release at the upper side. It is accompanied by transport of cations, in the present experiment K +, across the leaf. The resulting pH and K+ concentration changes near the leaf surface were recorded with miniature electrodes. From the pH and K+ concentration the concentrations of the different inorganic carbon species were calculated and compared with photosynthetic O, production. HCO⁻₃ utilization is accompanied by a drastic increase in the free CO₂ concentration near the lower epidermis. Experiments with CO₂− and HCO₃⁻free solutions showed an oscillating acidification near the lower epidermis and alkalinization near the upper epidermis. It is concluded that the acidification results from the activity of light-dependent H+ pumps. The finding that an increase in pH at the upper side always coincided with a decrease at the lower in these experiments shows that the H+ pumps and the OH− extruding mechanism are coupled although occurring in different cell layers. Previously we have suggested that the first step in the process of photosynthetic HCO₃⁻ utilization is external conversion of HCO₃⁻" by acidification caused by light-dependent H+ pumps. The present results strongly support this hypothesis. Two possible pathways for the accompanying K + transport are discussed. The model presented here explains the known inhibiting effects of buffers and high pH on photosynlhetic HCO₃⁻ utilization.     

Estimating thermal properties of simulated aquatic soils from their composition

Heat penetration and thermal lag in the submersed soil surrounding the roots of aquatic plants depends on two fundamental thermal properties of the substrate, volumetric heat capacity (C_V) and thermal conductivity (k). The relationship of these parameters to the fractions of organic and mineral matter, gas and water in natural and simulated aquatic soils was investigated. The gas fraction was found to be insignificant and it was possible to make good estimates of C_V and k from a knowledge of substrate water content alone.     

Relationships between culture density and the composition of three floating aquatic macrophytes

Eichhornia crassipes (Mart.) Solms, Pistia stratiotes (L.), and Lemna minor (L.) were cultured at four different densities each and analyzed for cell-wall fraction, crude protein, total available carbohydrate and ash. Cell-wall fraction increased and crude protein content decreased as density increased in Eichhornia and Pistia cultures. The cell-wall and crude protein content of Lemna did not change with increasing culture density. Differences in the trends of cell-wall and crude protein content of the three plants at increasing culture densities appear to be related to differences in growth form. There was no difference in the total available carbohydrate or ash content of the three species at different culture densities.     

The role of carbon dioxide in the formation of end-products by Hymenolepis diminuta

The hypothesis that ambient CO₂ levels determine the end-products of energy metabolism excreted by Hymenolepis diminuta was tested by incubating the parasite in a range of CO₂ concentrations and measuring internal concentrations of adenine nucleotides and the excretion of organic acids. The strain of H. diminuta used was found to excrete mainly lactic acid and acetic acid. Succinic acid production was generally less than 5–10% of the total. At high CO₂ concentrations, the rate of excretion of lactic acid decreased while that of succinic acid increased, which conforms with the hypothesis. Acetic acid excretion did not vary significantly over the range of CO₂ concentrations used. Other results did not support the hypothesis. High CO₂ levels reduced the total amounts of acids excreted and the rate of succinic acid excretion was so small as to be ineffective in preventing the accumulation of H⁺ ions. When present in the incubation medium, succinic acid was taken up by H. diminuta. Lactic and acetic acid excretion was always sufficient to limit the accumulation of H⁺ ions. The conditions of incubation were shown not to be responsible for the low rates of succinic acid excreted. Incubation conditions and metabolic end-products were found to affect the rates of excretion of organic acids. There is thus a need, in work of this nature, to regulate and specify experimental conditions and to stipulate the strain of parasite used. The hypothesis was rejected and it was suggested that the energy metabolism of parasitic helminths is adapted to fluctuating O₂ and CO₂ tensions.