Chemisorptions of bacterial receptors for hydrophobic amino acids and sugars on gold for biosensor applications: a surface plasmon resonance study of genetically engineered proteins

This paper demonstrates potential applications of two periplasmic receptor proteins from E coli as sensing elements for biosensors using the surface plasmon resonance (SPR) technique. These molecules, namely the aspartate to cysteine mutant of the leucine-specific receptor (LS-DIC) and the glutamine to cysteine mutant of the D-glucose/D-galactose receptor (GGR-Q26C) proteins, are chemisorbed on a thin (similar to40 nm) Au film in neutral K2HPO4 buffers. Using angle and time resolved SPR measurements; we show that adsorption behaviors of both proteins are dominated by diffusion-free second order Langmuir kinetics. We also show that the protein-modified Au films exhibit measurable SPR shifts upon binding to their respective target ligands. According to these SPR data, the kinetics of ligand binding for both LS-DIC and GGR-Q26C are governed by irreversible first order diffusion limited Langmuir model. The utility of the SPR technique for studying reactions of biological molecules is further illustrated in this work. (C) 2003 Elsevier B.V. All rights reserved

Oxazolidinone Synthesis through Halohydrin Dehalogenase-Catalyzed Dynamic Kinetic Resolution

An efficient dynamic kinetic resolution protocol using a single enzyme is described. Both the kinetic resolution and substrate racemization are catalyzed by halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC). The HheC-catalyzed reaction of epibromohydrin and 2-bromomethyl-2-methyloxirane with sodium cyanate afforded 5-substituted 2-oxazolidinones in high yields (97% and 87%) and high optical purity (89% and > 99% ee) in the presence of catalytic amounts of bromide ion. These compounds are valuable building blocks with diverse synthetic applications

Endogenous gibberellin profile during Christmas rose ( Helleborus niger L.) flower and fruit development

Gibberellins (GAs) were identified and quantified during flower and fruit development in the Christmas rose (Helleborus niger L.), a native of southeastern Europe with a long international horticultural tradition. Physiologically, the plant differs from popular model species in two major respects: (1) following anthesis, the initially white or rose perianth (formed in this species by the sepals) turns green and persists until fruit ripening, and (2) the seed is shed with an immature embryo, a miniature endosperm, and a prominent perisperm as the main storage tissue. GA1 and GA4 were identified by full-scan mass spectra as the major bioactive GAs in sepals and fruit. LC-MS/MS system in accord with previously verified protocols also afforded analytical data on 12 precursors and metabolites of GAs. In the fruit, GA4 peaked during rapid pericarp growth and embryo development and GA1 peaked during the subsequent period of rapid nutrient accumulation in the seeds and continued pericarp enlargement. In the sepals, the flux through the GA biosynthetic pathway was highest prior to the light green stage when the photosynthetic system was induced. Unfertilized, depistillated, and deseeded flowers became less green than the seed-bearing controls; chlorophyll accumulation could be restored by applying GA1, GA4, and, less efficiently, GA3 to the deseeded fruit. The sepals of unfertilized and depistillated flowers indeed contained very low levels of GA4 and gradually decreasing levels of GA1. However, the concentrations of their precursors and metabolites were less affected. These data suggest that a signal(s) from the fruit stimulates GA biosynthesis in the sepals resulting in greening. The fruit-derived GAs appear to be mainly involved in pericarp growth and seed development

Endogenous Auxin Profile in the Christmas Rose (Helleborus niger L.) Flower and Fruit: Free and Amide Conjugated IAA

The reproductive development of the Christmas rose (Helleborus niger L.) is characterized by an uncommon feature in the world of flowering plants: after fertilization the white perianth becomes green, photosynthetically active and persists during fruit development. In the flowers in which fertilization was prevented by emasculation (unfertilized) or entire reproductive organs were removed (depistillated), the elongation of the peduncle was reduced by 20 to 30%, and vascular development, particularly lignin deposition in sclerenchyma was arrested. Chlorophyll accumulation in sepals and their photosynthetic efficacy was up to 80% lower in comparison to fertilized flowers. Endogenous auxins were investigated in floral and fruit tissues and their potential roles in these processes were discussed. Analytical data of free indole-3-acetic acid (IAA), indole-3-ethanol (IEt), and seven amino acid conjugates were afforded by LC-MS/MS in floral tissues of fertilized as well as unfertilized and depistillated flowers. Among amino acid conjugates novel ones with Val, Gly, and Phe, were identified and quantified in the anthers, and in the fruit during development. Reproductive organs before fertilization, followed by developing fruit at post-anthesis were the main source of auxin. Tissues of unfertilized and depistillated flowers accumulated significantly lower level of auxin. Upon depistillation, auxin content in the peduncle and sepal was decreased to 4% and 45%, respectively, in comparison to fruit-bearing flowers. This study suggests that auxin arising in developing fruit may participate, in part, in coordination of the Christmas rose peduncle elongation and its vascular development