Nutrients are assimilated efficiently by Lymantria dispar caterpillars from the mature leaves of trees in the Salicaceae

The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71–81%) but significantly lower PAE from their mature leaves (45–52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68–76% and 72–92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high‐quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available.     

Altitudinal distribution limits of aquatic macroinvertebrates: an experimental test in a tropical alpine stream

1. Temperature and oxygen are recognised as the main drivers of altitudinal limits of species distributions. However, the two factors are linked, and both decrease with altitude, why their effects are difficult to disentangle. 2. This was experimentally addressed using aquatic macroinvertebrates; larvae of Andesiops (Ephemeroptera), Claudioperla, (Plecoptera), Scirtes (Coleoptera) and Anomalocosmoecus (Trichoptera), and the amphipod Hyalella in an Ecuadorian glacier‐fed stream (4100–4500 m a.s.l.). The following were performed: (i) quantitative benthic sampling at three sites to determine altitudinal patterns in population densities, (ii) transplants of the five taxa upstream of their natural altitudinal limit to test the short‐term (14 days) effect on survival, and (iii) in situ experiments of locomotory activity as a proxy for animal response to relatively small differences in temperature (5 °C vs. 10 °C) and oxygen saturation (55% vs. 62%). 3. The transplant experiment reduced survival to a varying degree among taxa, but Claudioperla survived well at a site where it did not naturally occur. In the in situ experiment, Scirtes and Hyalella decreased their activity at lower oxygen saturation, whereas Andesiops and Anomalocosmoecus did so at a low temperature. The decrease in activity from a high to a low temperature and oxygen for the five taxa was significantly correlated with their mortality in the transplant experiment. 4. Together the present experiments indicate that even relatively small differences in temperature and oxygen may produce effects explaining ecological patterns, and depending on the taxon, either water temperature or oxygen saturation, without clear interacting effects, are important drivers of altitudinal limits.     

Purification and characterization of recombinant human testis angiotensin-converting enzyme expressed in Chinese hamster ovary cells.

Enzymatically active human testis angiotensin-converting enzyme (ACE) was expressed in Chinese hamster ovary (CHO) cells stably transfected with each of three vectors: p omega-ACE contains a full-length testis ACE cDNA under the control of a retroviral promoter; and pLEN-ACEVII and pLEN-ACE6/5, in which full-length and membrane anchor-minus testis ACE cDNAs, respectively, are under the control of the human metallothionein IIA promoter and SV40 enhancer. In every case, active recombinant human testis ACE (hTACE) was secreted in a soluble form into the culture media, up to 2.4 mg/liter in the media of metal-induced, high-producing clones transfected with one of the pLEN vectors. In addition, membrane-bound recombinant enzyme was recovered from detergent extracts of cell pellets of CHO cells transfected with either p omega-ACE or pLEN-ACE-VII. Recombinant converting enzyme was purified to homogeneity by single-step affinity chromatography of conditioned media and detergent-extracted cell pellets in 85 and 70% overall yield, respectively. Purified hTACE from all sources comigrated with the native testis isozyme on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with M(r) approximately 100 kDa. The native and recombinant proteins cross-reacted equally with anti-human kidney ACE antiserum on Western blotting. The catalytic activity of recombinant angiotensin-converting enzyme, in terms of angiotensin I and 2-furanacryloyl-Phe-Gly-Gly hydrolysis, chloride activation, and lisinopril inhibition, was essentially identical to that of the native enzyme. The facile recovery in high yield of fully active hTACE from the media of stably transfected CHO cells provides a suitable system for investigating structure-function relationships in this enzyme.     

Side reaction in peptide synthesis. Formation of oxazolidone derivatives

2-Oxazolidone derivatives formed through an intramolecular reaction in the process of alkaline treatment of urethane-type N-protected peptides of which the N-terminal residues were Ser or Thr having unprotected hydroxyl groups. In oder to avoid this side reaction, the esters of these peptides could be cleaved by enzymatic hydrolyses instead of saponification.