Specificity studies of 3-mercaptopyruvate sulfurtransferase

3-Mercaptopyruvate sulfurtransferase (E.C. 2.8.1.2; MST) is an enzyme believed to function in the endogenous cyanide (CN) detoxification system because it is capable of transferring sulfur from 3-mercaptopyruvate (3-MP) to CN, forming the less toxic thiocyanate (SCN). To date, 3-MP is the only known sulfur-donor substrate for MST. In an effort to increase the understanding of what chemical properties of 3-MP affect its utilization as a substrate, in vitro enzyme kinetic studies of MST were conducted using two mercaptic acids that are structurally related to 3-MP. Neither of these compounds was able to serve as a sulfur-donor substrate for MST. Inhibitor studies determined that 3-mercaptopropionic acid did not affect the K_m of MST for 3-MP but did decrease V_max and, thus, was determined to be a noncompetitive inhibitor. Alternatively, 2-mercaptopropionic acid 2-MPA decreased K_m and V_max and was determined to be an uncompetitive inhibitor of MST with respect to 3-MP. These data indicate that the α-keto group of 3-MP is necessary for its utilization as a substrate, and the inhibitor studies suggest that the position of the sulfur may also affect the binding of these compounds to the enzyme. These observations increase the understanding of what factors can affect the utilization of a compound as a sulfur-donor substrate for MST and may aid in the development of alternative sulfur-donor substrates for MST. © 1996 John Wiley & Sons, Inc.     

Effects of Interactions BetweenPasteurella haemolyticaandBordetella parapertussisonin vitroPhagocytosis by Lung Macrophages

The aim of the work was to determine the effect of exposing ovine bronchoalveolar macrophages (BAM)in vivotoPasteurella haemolyticaand/orBordetella parapertussison the subsequent uptake and killing ofP. haemolyticaby these cellsin vitro. Exposurein vivotoP. haemolyticadid not affect the uptake ofP. haemolyticaby BAMin vitrobut reduced (P< 0·05) the intracellular killing of bacteria. Exposurein vivotoB. parapertussishad no significant effect on either the uptake of killing ofP. haemolytica in vitro. However, sequential exposurein vivotoB. parapertussisandP. haemolyticareduced both the ingestion (P< 0·05) and killing (P< 0·001) ofP. haemolytica in vitro. These results indicate that exposure toP. haemolyticacompromised the bacterial killing mechanisms of BAM and that synergy betweenB. parapertussisandP. haemolyticareduced the ability of BAM to ingest bacteria.     

Decompression comparison of helium and hydrogen in rats

Lillo, R. S., E. C. Parker, and W. R. Porter.Decompression comparison of helium and hydrogen in rats.J. Appl. Physiol. 82(3): 892-901, 1997.The hypothesis that there are differences in decompression riskbetween He and H₂ wasexamined in 1,607 unanesthetized male albino rats subjected to dives on2% O₂-balance He or 2%O₂-balanceH₂ (depths  50 ATA, bottom times  60 min). The animals were decompressed to 10.8 ATA with profilesvarying from rapid to slow, with up to four decompression stops of up to 60 min each. Maximum likelihood analysis was used to estimate therelative decompression risk on a per unit pressure basis (termed "potency") and the rate of gas uptake and elimination, bothfactors affecting the decompression sickness risk, from a specific dive profile. H₂ potency for causingdecompression sickness was found to be up to 35% greater than that forHe. Uptake rates were unresolvable between the two gases with the timeconstant (TC) estimated at ~2-3 min, leading to saturation inboth cases in <15 min. Washout of both gases was significantly slowerthan uptake, with He washout (TC ~1.5-3 h) substantially slowerthan H₂ washout (TC ~0.5 h). Itis unknown whether the decompression advantage of the faster washout ofH₂ or the disadvantage of itsincreased potency, observed in the rat, would be important for humandiving.

     

A followup study of the academic attainment and classroom behavior of children with elevated dentine lead levels

To investigate the impact of low-level lead exposure on children's behavior within a natural setting, we assessed the school performance of a sample of 141 elementary school children classified according to dentine lead level. Twenty-two children had “elevated” levels (≥20 parts per million), 71 had “midrange” levels (10.0–19.9 parts per million), and 48 had “low” levels (<10 parts per million). Four types of outcome data were collected: (1) scores on a standardized group intelligence test, (2) teachers' ratings, (3) incidence of academic failure (assignment to remedial aid, grade retention), and (4) observations of classroom behavior. In general, higher dentine lead levels were associated with less favorable school performance, with most covariance-adjustedp-values in the range of 0.05–0.15. The incidence of grade retention was the outcome most strongly related to lead level. The pattern of results suggests a consistent, though weak relationship between children's dentine lead levels and elementary school performance.     

The fluorescence decay kinetics of in vivo chlorophyll measured using low intensity excitation

We report fluorescence lifetimes for in vivo chlorophyll a using a time-correlated single-photon counting technique with tunable dye laser excitation. The fluorescence decay of dark-adapted chlorella is almost exponential with a lifetime of 490 ps, which is independent of excitation from 570 nm to 640 nm.Chloroplasts show a two-component decay of 410 ps and approximately 1.4 ns, the proportion of long component depending upon the fluorescence state of the chloroplasts. The fluorescence lifetime of Photosystem I was determined to be 110 ps from measurements on fragments enriched in Photosystem I prepared from chloroplasts with digitonin.     

Developmental Parameters of Mother-Offspring Interactions in Acomys cahirinus

Developmental parameters of mother-infant interactions in Acomys cahirinus were investigated in a series of observational and experimental studies. The uniquely precocial offspring associated closely with both parents beyond the time of weaning and birth of the next litter. The survival rate of foster pups was dependent upon both the age of the pups and the physiological stare of the foster mothers. While 1 and 8-day post partum ♂♂ nursed unfamiliar neonates as frequently as their own pups, they interacted with unfamiliar 8-day-old offspring less than with their own.     

Preparation of protoplasts from the green alga Enteromorpha intestinalis (L.) Link

Protoplasts have been obtained from vegetative thallus of the green seaweed Enteromorpha following enzymic digestion with driselase and pectinase. The viability of purified protoplast fractions was assessed by staining and measurements of O₂ uptake and evolution.Abbreviations MES 2-(N-morpholino) ethanesulphonic acid - TES N-tris(hydoxymethyl) methyl-2 aminoethanesulphonic acid