Influence of the carboxyl terminus of luteinizing hormone-releasing hormone and bradykinin on hydrolysis by brain endo-oligopeptidases

A homogeneous preparation of endo-oligopeptidase A from rabbit brain cleaves luteinizing hormone-releasing hormone (less than Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) at the Tyr-Gly bond only after the removal of Gly-NH2 from the COOH-terminal position of the molecule. The influence of the carboxyl terminus on hydrolysis by brain endo-oligopeptidases was studied using bradykinin as a model substrate. The substitution of the carboxyl group of bradykinin by the amide reduces by 2.5-fold the rate of Phe-Ser bond hydrolysis by endo-oligopeptidase A but has no effect on the rate of hydrolysis of the Pro-Phe bond by endo-oligopeptidase B. On the other hand, the deletion of Phe-Arg from the COOH-terminal portion of bradykinin makes the peptide resistant to hydrolysis by endo-oligopeptidase A whereas it increases by 5-fold the rate of hydrolysis of the Pro-Gly bond by endo-oligopeptidase B.     

Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.     

Plant defense against leaf herbivory based on metal accumulation: examples from a tropical high altitude ecosystem

Species that evolved in high‐altitude grasslands, where soils are dystrophic and metal rich, developed adaptations for these extreme conditions, such as metal accumulation and sclerophyllous leaves, and these adaptations may secondarily affect insect herbivory activity. The present study investigates the hypothesis that costs related to accumulation of certain metals may be evolutionarily compensated for by decreasing leaf herbivory in some plant species from rupestrian fields. Studies were conducted in different locations at the Ferriferous Quadrangle, a metal‐rich region in south‐east Brazil, with four species adapted to high‐altitude grasslands: Eremanthus erythropappus, Eremanthus incanus, Lychnophora ericoides and Byrsonima variabilis. Sample design varied according to population sizes and spatial distribution of individuals. We found that concentrations of manganese (Mn) and iron (Fe) significantly reduced the herbivory in the leaves of E. erythroppapus and E. incanus, whereas aluminum (Al) reduced herbivory in L. ericoides, and Mn affected negatively the herbivory in B. variabilis. These results support the hypothesis that metal‐accumulating plants, as a response to the harsh environment in which they evolved, are protected against foliar damage caused by insect herbivores in rupestrian fields.     

Degradation of neurotensin by rabbit brain endo-oligopeptidase A and endo-oligopeptidase B (proline-endopeptidase)

The degradation of neurotensin and D-Tyr11 neurotensin by apparently homogeneous preparations of rabbit brain endo-oligopeptidase A and endo-oligopeptidase B (Proline-endopeptidase) was studied. Peptide fragments were isolated by high performance liquid chromatography and identified by amino acid analysis. Endo-oligopeptidase A cleaved neurotensin at the Arg8-Arg9 bond whereas D-Tyr11 neurotensin was not significantly hydrolysed. Endo-oligopeptidase B cleaved at the carboxyl side of Pro7, Pro10 in neurotensin and at Pro7 in D-Tyr11 neurotensin. The concentration dependent inhibition of neurotensin degradation by bradykinin and vice-versa represents additional evidence that endo-oligopeptidase A cleaves both Phe5-Ser6 bond of bradykinin and the Arg8-Arg9 bond of neurotensin.