Boophilus microplus: characterization of larval phosphomonoesterases and isolation of subcellular fractions with high phosphatase activity.

Phosphomonoesterase activity was determined for a 115,000g pellet and soluble fractions resulting from a subcellular fractioning of a homogenate of larval Boophilus microplus. Both fractions showed maximum phosphatase activity at pH 5.5 and 10. Acid phosphatase (EC 3.1.3.2) activity was found to be greatest in the soluble fraction. When the reaction rate was plotted against homogenate concentration, the soluble acid phosphatase deviated from the linear relationship. For both fractions different thermostability patterns were obtained, inactlvation beginning for the alkaline phosphatase (EC 3.1.3.1) at 45–55 C. When the effect of substrate concentration on activity was studied, deviations from the typical hyperbolic behavior were observed. Homogenization of larvae with 5 mm EDTA buffer failed to yield a low-speed pellet with high alkaline phosphatase activity, as it is expected if absorptive structures sediment. Moreover, total alkaline phosphatase activity recovered by this method is significantly lower than activity recovered when homogenization is carried out without EDTA. Alternately, homogenization with 10 mM Tris buffer and 0.25 M sucrose gave 27,000g and 115,000g fractions with high phosphatase activity when fractioned by centrifugation. Alkaline treatment of the 115,000g fraction with 10 mM Tris buffer, pH 7.8, failed to separate endoplasmic reticulum contaminants without loss of phosphatase activity. When the 115,000g fraction was centrifuged in a sucrose density gradient, two activity peaks, coincident for both acid and alkaline phosphatases, were obtained. Antigenic analysis showed the existence of similar antigenic determinants in both peaks “immunologically” presented in different ways.     

Thymineless death inLactobacillus acidophilus R-26

Thymineless death (TLD) as well as deoxyribosideless death (DRLD) can be observed inLactobacillus acidophilus R-26 during growth in media lacking thymine or deoxyriboside respectively. Both phenomena exhibit the same interval of lage period (2–3 h) but the rate of inactivation is 2–3 times faster in TLD. Transfer experiments show that inactivation of bacterial reproduction is accelerated immediately if—DR medium is replaced by—T one. In the opposite case the deceleration of the inactivation rate does not appear immediately but after a 1–2 h lag period, in which no changes in the number of viable bacteria can be observed. Our results suggested that the accumulation of deoxyriboside compounds has no causal role in the inactivation of bacterial reproduction. However, the presence of deoxyribosides can accelerate the process of inactivation.     

Differential inactivation of plant lauric acid omega- and in-chain-hydroxylases by terminally unsaturated fatty acids

The microsomal fraction from Vicia sativa L. cv. Septimane contains a cytochrome P-450-dependent lauric acid omega-hydroxylase that is inactivated in a time-dependent, pseudo-first-order manner when the microsomes are incubated with 11-dodecynoic acid. The rate constant for the inactivation is approximately 4.3-4.8 X 10(-3) s-1. In contrast, the olefinic analog 11-dodecenoic acid is primarily a time-independent inhibitor of the omega-hydroxylase. 1-Aminobenzotriazole, 3-phenoxy-1-propyne, and 3-(2,4-dichlorophenoxy)-1-propyne, mechanism-based inactivators of cinnamic acid 4-hydroxylase, and 9-decenoic acid, a mechanism-based inactivator of the lauric acid in-chain hydroxylase, are at best poor inactivators of the omega-hydroxylase. Conversely, cinnamic acid 4-hydroxylase is only slightly affected by concentrations of 11-dodecynoic acid that completely inactivate the omega-hydroxylase. 11-Dodecynoic acid is thus a potent, relatively specific, inactivator of the V. sativa lauric acid omega-hydroxylase.     

Leaf size of woody dicots predicts ecosystem primary productivity

A key challenge in ecology is to understand the relationships between organismal traits and ecosystem processes. Here, with a novel dataset of leaf length and width for 10 480 woody dicots in China and 2374 in North America, we show that the variation in community mean leaf size is highly correlated with the variation in climate and ecosystem primary productivity, independent of plant life form. These relationships likely reflect how natural selection modifies leaf size across varying climates in conjunction with how climate influences canopy total leaf area. We find that the leaf size?primary productivity functions based on the Chinese dataset can predict productivity in North America and vice‐versa. In addition to advancing understanding of the relationship between a climate‐driven trait and ecosystem functioning, our findings suggest that leaf size can also be a promising tool in palaeoecology for scaling from fossil leaves to palaeo‐primary productivity of woody ecosystems.     

A trophic cascade initiated by an invasive vertebrate alters the structure of native reptile communities

Invasive vertebrates are frequently reported to have catastrophic effects on the populations of species which they directly impact. It follows then, that if invaders exert strong suppressive effects on some species then other species will indirectly benefit due to ecological release from interactions with directly impacted species. However, evidence that invasive vertebrates trigger such trophic cascades and alter community structure in terrestrial ecosystems remains rare. Here, we ask how the cane toad, a vertebrate invader that is toxic to many of Australia's vertebrate predators, influences lizard assemblages in a semi‐arid rangeland. In our study area, the density of cane toads is influenced by the availability of water accessible to toads. We compared an index of the abundance of sand goannas, a large predatory lizard that is susceptible to poisoning by cane toads and the abundances of four lizard families preyed upon by goannas (skinks, pygopods, agamid lizards and geckos) in areas where cane toads were common or rare. Consistent with the idea that suppression of sand goannas by cane toads initiates a trophic cascade, goanna activity was lower and small lizards were more abundant where toads were common. The hypothesis that suppression of sand goannas by cane toads triggers a trophic cascade was further supported by our findings that small terrestrial lizards that are frequently preyed upon by goannas were more affected by toad abundance than arboreal geckos, which are rarely consumed by goannas. Furthermore, the abundance of at least one genus of terrestrial skinks benefitted from allogenic ecosystem engineering by goannas where toads were rare. Overall, our study provides evidence that the invasion of ecosystems by non‐native species can have important effects on the structure and integrity of native communities extending beyond their often most obvious and frequently documented direct ecological effects.     

New Approaches for Absolute Quantification of Stable‐Isotope‐Labeled Peptide Standards for Targeted Proteomics Based on a UV Active Tag

Targeted proteomics depends on the availability of stable isotope labeled (SIL) peptide standards, which for absolute protein quantification need to be absolutely quantified. In the present study, three new approaches for absolute quantification of SIL peptides are developed. All approaches rely on a quantification tag (Qtag) with a specific UV absorption. The Qtag is attached to the peptide during synthesis and is removed by tryptic digestion under standard proteomics workflow conditions. While one quantification method (method A) is designed to allow the fast and economic production of absolutely quantified SIL peptides, two other methods (methods B and C) are developed to enable the straightforward re‐quantification of SIL peptides after reconstitution to control and monitor known problems related to peptide solubility, precipitation, and adhesion to vials. All methods yield consistent results when compared to each other and when compared to quantification by amino acid analysis. The precise quantitation methods are used to characterize the in vivo specificity of the H3 specific histone methyltransferase EZH2.