Polyphenol Oxidase Produced During Encystation of Acanthamoeba castellanii

Acanthamoeba castellanii has a phenol oxidase activity that is believed to be a laccase. Enzyme activity was found in the outer cyst wall, in the cytoplasm of encysting amoebae and in the encystment medium. Encystment procedures were modified to promote an increase in the amount of soluble enzyme secreted during encystation. Acanthamoeba polyphenol oxidase has a pH optimum of 6.0 and a K_m value of 0.21 mM with dihydroxyphenylalanine. The enzyme does not oxidize tyrosine, and it is inhibited by chloride but not by inhibitors of peroxidase. Its synthesis coincides with encystation. and known inhibitors of polyphenol oxidase prevent encystation. Polyphenol oxidase may have a role in making the cyst resistant to mechanical and chemical breakdown.     

The Organic Acid Metabolism of Bramley's Seedling Apple Peel1

1. The effect of various Krebs cycle acids on the respirationofdisks of apple peel at various stages of maturity was measuredin a Warburg respirometer.
2. Peel tissue from apples at thepre-climacteric and early post-climactericstages apparentlycontain sufficient of the Krebs cycle acidsused, with the exceptionof succinate, to maintain oxidativeprocesses at a maximum.
3. The addition of malate causes a large increase in the CO₂-outputof peel from post-climacteric and senescent fruit but not frompre-climacteric fruit, and a close correlation exists betweenthe climacteric and this decarboxylation of malate. The decarboxylationof malate does not affect the rate of O₂-uptake of peel tissue.The possible part played by the decarboxylation of malate inthe increased CO₂-output at the climacteric is discussed.
4. Addedpyruvate is decarboxylated by the tissue at all stagesof storagelife.
5. The decarboxylation of added malate is an aerobic fermentation,resulting in the quantitative production of acetaldehyde. Althoughthe presence of oxygen is necessary, the rate of O₂-uptake isnot affected by the reaction. Pyruvate decar boxylation doesnot require the presence of oxygen.
6. The O₂-uptake of peelfrom senescent apples can be stimulatedby addition of malate,succinate, and a-ketoglutarate. No evidencewas obtained, however,of oxidation of fumarate, citrate, orpyruvate. The additionof malate to senescent tissue restoresthe lower endogenousrate of O₂-uptake to that of early postclimacteric tissue.
7. Succinate and fumarate are toxic to peel tissue at concentrationabove 0.02M.

     

In Vitro Excystation of Spironucleus muris

ABSTRACT. In vitro excystation of Spironucleus muris cysts, purified by sequential sucrose and Percoll gradients from mouse feces, was studied. Three in vitro excystation procedures, used for Giardia , were assessed to determine the most useful method. Excystation was monitored by light microscopy and subsequently characterized by transmission and scanning electron microscopy. Spironucleus muris excysted routinely at a level greater than 90% when induced in Hanks' balanced salt solution containing sodium bicarbonate at pH 2.0 and transferred to Tyrodes' salt solution as an excystation medium. Similarly, high rates of excystation were recorded after induction of S. muris cysts in 0.1 M potassium phosphate buffer (pH 7.0) with sodium bicarbonate and excystation in trypticase-yeast extract-iron medium (TYI medium) or phosphate-buffered saline. A lower rate and percentage of excystation were observed after induction of S. muris cysts in an aqueous hydrochloric acid solution (pH 2.0) followed by excystation in TYI medium. All excystation methods produced extremely active S. muris trophozoites with normal morphology. Nonexcysting S. muris cysts have a wall composed of an outer fibrous and an inner membranous portion. Following induction, numerous vesicles appeared in the peritrophic space. Excystation began by the cyst wall opening at one pole, and the anterior part of the trophozoite protruding from the cyst wall. The trophozoite emerged progressively from the cyst wall and the empty cyst wall appeared to collapse. Excysted trophozoites exhibited normal morphological features of S. muris trophozoites isolated from the mouse intestine.     

Variable chemical defence in the checkerspot butterfly Euphydryas gillettii (Lepidoptera: NymphaIidae)

Abstract.

• 1 Like other checkerspots, Euphydryas gillettii butterflies may contain the defensive chemicals, iridoid glycosides, which are sequestered from their hostplants during larval feeding.
• 2 We analysed the iridoid glycoside content of E.gillettii adults from two different populations, Warm Lake, Idaho, and Granite Creek, Wyoming, that have different patterns of hostplant use.
• 3 Gas chromatographic analysis of thirty butterflies from the Wyoming population showed that they contained a mean of 1.27 (±0.19 SE) % dry weight iridoid glycosides. Notably, 20% of these butterflies contained no detectable iridoid glycosides.
• 4 In contrast, nineteen butterflies from the Idaho population contained a mean of 3.89 (±0.38 SE) % dry weight iridoid glycosides, and all butterflies contained iridoid glycosides.
• 5 These results illustrate how the chemical defence of herbivorous insects varies according to differential use of potential hostplants.

     

Collective Action and Social Capital of Wildlife Management Associations

Abstract: In areas with dense landownership patterns, management of white-tailed deer (Odocoileus virginianus) depends upon collective decision making of landowners and hunters. To resolve conflicts associated with this commons dilemma, wildlife management associations (WMAs) have become a popular mechanism for coordinating wildlife management decisions in private land states, especially in Texas, USA. Social capital, represented by metrics such as trust, reciprocity, and community involvement, has been identified as an important determinant of the success of collaborative institutional arrangements. To determine the influence of social capital on the effectiveness of WMAs, we address 2 research questions: 1) do WMAs exhibit elements of social capital, and 2) what landowner characteristics affect elements of social capital within WMAs? We used a mail survey questionnaire to determine the effect of various factors on the activities and management practices in 4 WMAs in 2 regions in Texas: the Lower Post Oak Savannah (LPOS) and the Central Post Oak Savannah (CPOS). The LPOS landowners were members of larger associations, had generally acquired their land more recently, held more frequent meetings, and tended to have longer association membership than CPOS landowners, yet they exhibited lower social capital. The CPOS landowners owned significantly larger properties, and were predominantly absentee wealthy males that considered relaxation and hunting more important land uses than property ownership for a place to live. The smaller group size of the CPOS associations may be the most important factor in building and maintaining social capital. Intra-association trust, a primary measure of social capital, was positively influenced by the longevity of property ownership, the number of association meetings, the percentage of males in the association, and other factors. Conversely, negative influences on trust included absentee ownership and the proportion of woodland habitat present in each WMA. We suggest that deer are a common-pool resource whose populations are dependent upon collective action by stakeholders. Social capital building within landowner associations could facilitate the sustainable harvest of quality deer and possibly lead to cooperative management of other common-pool natural resources.