Lipolytic activity of ricin from Ricinus sanguineus and Ricinus communis on neutral lipids.

The present study was carried out with a view of determining ricin lipolytic activity on neutral lipids in emulsion and in a membrane-like model. Using 2,3-dimercapto-1-propanol tributyrate (BAL-TC(4)) as substrate, the lipolytic activity of ricin was found to be proportional to ricin and substrate concentrations, with an apparent K(m) (K(m,app)) of 2.4 mM, a k(cat) of 200 min(-1) and a specific activity of 1.0 unit/mg of protein. This work was extended to p-nitrophenyl (pNP) fatty acid esters containing two to twelve carbon atoms. Maximum lipolytic activity was registered on pNP decanoate (pNPC(10)), with a K(m,app) of 3.5 mM, a k(cat) of 173 min(-1) and a specific activity of 3.5 units/mg of protein. Ricin lipolytic activity is pH and galactose dependent, with a maximum at pH 7.0 in the presence of 0.2 M galactose. Using the monolayer technique with dicaprin as substrate, ricin showed a lipolytic activity proportional to the ricin concentration at 20 mN/m, which is dependent on the surface pressure of the lipid monolayer and is detectable up to 30 mN/m, a surface pressure that is of the same order of magnitude as that of natural cell membranes. The methods based on pNPC(10) and BAL-TC(4) hydrolysis are simple and reproducible; thus they can be used for routine studies of ricin lipolytic activity. Ricin from Ricinus communis and R. sanguineus were treated with diethyl p-nitrophenylphosphate, an irreversible serine esterase inhibitor, and their lipolytic activities on BAL-TC(4) and pNPC(10), and cytotoxic activity, were concurrently recorded. A reduction in lipolytic activity was accompanied by a decrease in cytotoxicity on Caco2 cells. These data support the idea that the lipolytic activity associated with ricin is relevant to a lipase whose activity is pH and galactose dependent, sensitive to diethyl p-nitrophenylphosphate, and that a lipolytic step may be involved in the process of cell poisoning by ricin. Both colorimetric tests used in this study are sensitive enough to be helpful in the detection of possible lipolytic activities associated with other cytotoxins or lectins.

Raising the curtain on the gray region.

The gray region in EPA Document QA/G-4 is defined as the range of possible parameter values near the action level where the cost of determining that the alternative condition is true outweighs the expected consequences of a decision error. The gray region is also described as a range of true parameter values within the alternative condition near the action level where it is "too close to call." EPA Document QA/G-4HW states that during the planning stage the action level is based on an ideal decision rule, while during the assessment stage an operational decision rule is used. This paper analyzes the factors that define the gray region and the action level, including the errors of the first kind (a) and second kind (beta) and the number of samples taken to determine the mean result. The relationship between the Decision Performance Curve presented in EPA QA/G-4 and the statistical power curve is also discussed. The statistically derived critical level is identified as the concentration of importance for decision-making. The action level is defined in terms of the critical level so that its value is consistent for decisions made during both planning (a priori decisions) and assessment (a posteriori decisions).

Ricin RCA60: evidence of its phospholipase activity.

The present work documents, on a qualitative and quantitative basis, the lipolytic activity of ricin protein RCA60 on glycerophospholipids. RCA60 demonstrates a low level of hydrolysis towards radioactive dipalmitoyl-glycerophosphatidylcholine. This observation was confirmed on a better substrate, palmitoyl-oleoyl-glycerophosphatidylcholine, after analysis of the reaction products by thin-layer and gas chromatography. A comparable hydrolytic activity was observed when palmitoyl-oleoyl-glycerophosphatidylethanolamine was used as substrate. The nature of the hydrolysis products supports the conclusion that RCA60 demonstrates phospholipase A1 and A2 activities as well as a lysophospholipase activity of A1 and A2 type. The insensitivity of this lipolytic activity towards calcium ions and the presence of the already described consensus sequence of lipases, Gly-Xaa-Ser-Xaa-Gly, in the primary sequence of the B-chain of RCA60 support the idea that the lipolytic activity of RCA60 is more related to the lipase family than to the phospholipases A. We hypothesize that such activity contributes to the mechanism which underlies the expression of the cytotoxicity of RCA60.

[A program for personnel staffing in a nursing service]. / 'n Program vir personeelvoorsiening in 'n verpleegdiens.

A staffing programme for a nursing service in a private hospital can be very costly. The aim with this study was to describe and implement a staffing programme for a nursing service in a private hospital and to determine the success thereof by means of a cost-analysis. An exploratory, descriptive and instrumental research design was employed. The cost saving was statistically significant without jeopardizing the quality of nursing care. It is recommended that a staffing programme be implemented in private hospitals to improve cost-effectiveness.

Catabolism of leukotriene A4 into B4, C4, and D4 by rat liver subcellular fractions.

[3H]Leukotriene A4 was incubated with various subcellular fractions of rat liver homogenates. After solvent extraction and purification on C18 Sep-Pak cartridges, tritiated products migrating on reversed-phase HPLC with authentic unlabelled leukotriene C4, D4 and B4 were observed. The identity of leukotriene C4 was confirmed through enzymatic conversion into D4 by gamma-glutamyl transpeptidase as well as by bioassay on the rat stomach fundus after HPLC purification. The contractile response to the extracted material was blocked by the SRS antagonist, FPL 55712. Leukotriene B4 synthesis was located in the 100 000 X g supernatant, while C4 synthesis was present in the corresponding pellet. Leukotriene C4 formation was enhanced when reduced glutathione was supplemented in the incubation medium. These results demonstrate the presence in rat liver of various enzymatic steps in leukotriene A4 catabolism.

The effect of the dye-marking of mastitis remedies on the incidence of antibiotic residues in Pretoria's market milk supplies.

A 1973 survey on the incidence of inhibitory substances (mostly antiobiotic residues) in market milk supplied in Pretoria, on 3 195 herd milk samples, 65 tanker milk samples and 252 samples of pasteurised milk using the disc assay procedure with Bacillus stearothermophilus C 953 as test organism, revealed inhibitory substances equivalent to 0,005 IU penicillin/ml in 7.8% of the herd samples, 29,2% of the tanker samples and in 38.5% of the samples of pasteurised milk. In 38.9% of the positive herd milk samples and 73% of the samples of pasteurised milk, penicillin was indentified with the aid of the penicillinase test. Some of the pasteurised milk contained inhibitory substances equivalent to more than 1.0 IU penicillin/ml; in some of the herd milk samples this figure exceeded 5,0 IU penicillin/ml. A repeat survey was undertaken in 1977/78 to evaluate the effect of compulsory dye-marking of non-prescription mastitis remedies on the situation. In a total of 1 081 herd milk samples, 60 tanker milk samples and 112 samples of pasteurised milk, antibiotic residues were found in 2,13% of the herd milk, 11,7% of the tanker milk and 2,1% of the pasteurised milk samples, with a much lower average concentration of antibiotic residues. The compulsory dye-marking of mastitis remedies had a beneficial effect on the occurrence of antibiotic residues in milk but did not ensure their complete absence, presumably because dye-marking was not made compulsory in scheduled preparations.

[UHT--behandeling van melk (author's transl)].

Pasteurisation of milk provides protection for the consumer against pathogens which may be present in the raw milk, and improves its keeping quality. Sterilisation provides indefinite keeping quality but has an undesirable effect on the flavour and nutritive value of the milk. Ultra high temperature (UHT) treatment produces a milk with prolonged shelf life at ambient temperatures yet has practically the same effect on colour, falvour and nutritive value as pasteurisation. UHT treatment of milk involves preheating to 80 degrees C and then quickly raising the temperature, either by indirect heating in a tubular heater or by direct steam injection, to 130 degrees-- to 150 degrees C at which temperature it is kept for 3 to 5 sec. Cooling follows immediately. Systems in operation in South Africa use steam injection for heating to sterilising temperatures. Evaporation cooling is obtained by subjecting milk to a partial vacuum. This removes any water added during heating by condensing steam and also removes steam-volatile off-flavours. UHT-treated milk is packed aseptically, usually into heat-sealed paperboard laminated cartons. Intact packages can be kept for up to three months. Absolute sterility cannot be obtained by UHT processing. The term "sterilising effect", introduced by Galesloot, means the log10 of the ratio of initial spore count to surviving spore count. A spoilage rate of not more than one litre package per 1000 is considered satisfactory. For laboratory control samples of the sterilized milk are incubated at temperatures favourable to germination of mesophilic and thermophilic spores respectively. After incubation the milk is examined for flavour and physical appearance, subjected to the standard plate count and tested for increase in acidity and decrease in stability towards the alcohol test. Milk for UHT treatment must possess protein stability in the alcohol test, be of good bacteriological quality, and a low spore count in particular.