Plant‐mediated effects of soil nitrogen enrichment on a chemically defended specialist herbivore,Calophasia lunula

1. Nitrogen enrichment is an important driver of environmental change. In the present study, plant‐mediated effects of increased nitrogen on a specialist herbivore, Calophasia lunula Hufnagel, which sequesters antirrhinoside, an iridoid glycoside produced by its host plants, were examined. 2. Caterpillars were reared on Linaria dalmatica plants grown under low or high N treatments, and C. lunula performance traits and antirrhinoside levels were measured. Additionally, a bioassay was conducted with predatory ants to examine their response to antirrhinoside. 3. Nitrogen enrichment increased larval biomass and decreased larval antirrhinoside concentrations, but had no effect on plant iridoid glycoside concentrations or larval antirrhinoside content. Thus, differences in larval antirrhinoside concentrations were evidently a consequence of increased larval biomass. Additionally, nitrogen treatment had no effects on pupal performance or defence traits. 4. Bioassay results demonstrated a deterrent effect of antirrhinoside, but additional tests are necessary to evaluate the defensive role of this compound in insects. 5. Surprisingly, this study demonstrated little effect of a six‐fold increase in nitrogen availability on L. dalmatica iridoid glycoside concentrations or sequestration by C. lunula. Moreover, the results suggested that changes in plant primary chemistry were more important than secondary chemistry for this specialist herbivore, and that some insects may be insensitive to N enrichment.     

Screening of Commercial Enzymes for Transfructosylation of Tyrosol: Effect of Process Conditions and Reaction Network

Enzymatic fructosylation of organic acceptors other than saccharides brings new possibilities to synthesize molecules that do not exist in nature. The introduction of fructosyl moiety may lead to glycosides possessing enhanced physicochemical and bioactive properties which could be useful in the pharmaceutical and cosmetic industry. In this work, the regioselective synthesis of tyrosol β‐d ‐fructofuranoside (TF) catalyzed by β‐fructofuranosidase is investigated. In the first step, 32 commercial enzyme preparations are screened for fructoside‐hydrolyzing activity. The most active preparations are subsequently examined for fructofuranosyl transfer from sucrose to tyrosol. The best candidate, Novozym 188, is chosen to study the effect of reaction conditions on the product formation in a batch reactor. The effects of substrate concentration, temperature, pH, time, and enzyme dosage on the concentration of TF produced are studied using the design of experiments methodology. The maximal product concentration of 3.8 g L^?1 is achieved for the sucrose concentration of 1.5 m , tyrosol concentration of 29 g L^?1, temperature of 41 °C, and pH 5.1. Besides the main transfructosylation reaction between sucrose and tyrosol, several side reactions take place. A reaction network includes also the formation of fructooligosaccharides and the hydrolysis of sucrose and all reaction products.     

A critical survey of average distances between catalytic carboxyl groups in glycoside hydrolases

Published X‐ray crystallographic structures for glycoside hydrolases (GHs) from 39 different families are surveyed according to some rigorous selection criteria, and the distances separating 208 pairs of catalytic carboxyl groups (20 α‐retaining, 87 β‐retaining, 38 α‐inverting, and 63 β‐inverting) are analyzed. First, the average of all four inter‐carboxyl O^…O distances for each pair is determined; second, the mean of all the pair‐averages within each GH family is determined; third, means are determined for groups of GH families. No significant differences are found for free structures compared with those complexed with a ligand in the active site of the enzyme, nor for α‐GHs as compared with β‐GHs. The mean and standard deviation (1σ) of the unimodal distribution of average O^…O distances for all families of inverting GHs is 8 ± 2Å, with a very wide range from 5Å (GH82) to nearly 13Å (GH46). The distribution of average O^…O distances for all families of retaining GHs appears to be bimodal: the means and standard deviations of the two groups are 4.8 ± 0.3Å and 6.4 ± 0.6Å. These average values are more representative, and more likely to be meaningful, than the often‐quoted literature values, which are based on a very small sample of structures. The newly‐updated average values proposed here may alter perceptions about what separations between catalytic residues are “normal” or “abnormal” for GHs. Proteins 2014; 82:1747–1755. © 2014 Wiley Periodicals, Inc.