Fluorescence and photoacoustic spectroscopy of immobilized thylakoids

Monitoring electron transfer by photoacoustic spectroscopy in native and immobilized thylakoid membranes

Photoacoustic spectroscopy was used to monitor photo synthetic electron transfer in native and immobilized thylakoid membranes. The photoacoustic parameter phi(r)' (the percentage of absorbed energy that is stored in photo chemical intermediates) and i(50) (the half-saturation modulated light intensity) were directly correlated to electron transfer rates. As previously shown, thylakoids immobilized in an albumin-glutaraldehyde matrix were more resistant to aging. The inhibitory effects of the immobilization procedure and of aging at 4 degrees C were detected as a decrease in i(50) values. In analogy with enzyme kinetic analysis, the effect could be characterized as a competitive type of inhibition. Photoacoustic measurements are performed in conditions similar to a working bioreactor cell with regards to the sample preparation.

Micro-algal biosensors

Fighting against water pollution requires the ability to detect pollutants for example herbicides or heavy metals. Micro-algae that live in marine and fresh water offer a versatile solution for the construction of novel biosensors. These photosynthetic microorganisms are very sensitive to changes in their environment, enabling the detection of traces of pollutants. Three groups of micro-algae are described in this paper: chlorophyta, cyanobacteria, and diatoms.

Comparative study of thylakoid membranes sensitivity for herbicide detection after physical or chemical immobilization

A micro-test using immobilized thylakoid membranes as sensing element in a micro-electrochemical cell has been developed to assess impairment at the level of the light-driven transport of electrons. In this study, thylakoids isolated from spinach leaves were either immobilized by entrapment in poly(vinylalcohol) bearing styrylpyridinium groups or by chemical immobilization in an albumin-glutaraldehyde crosslinked matrix. The two immobilization procedures were compared upon the sensitivity of the immobilized materials to detect nine herbicides targetting photosystem II. Despite the largely differing mode of immobilization, the procedures led to strikingly similar detection capabilities for herbicides. Inherent characteristics of both immobilization procedures are also discussed.

Modulation by a high citrate concentration of kinetic parameters and of functional stability of two immobilized thylakoid systems

This article deals with aspects of the reciprocal interaction between the activity of chloroplast membranes and their microenvironment. The artificial matrices used in the present work to immobilize thylakoids (albumin-glutaraldehyde matrix, polyurethane foam) can be regarded as weak ion exchangers. Thus, the distribution of the solute between the matrix surface and the external solution should, at least in part, be governed by a Donnan equilibrium. The influence of a high ionic strength medium (750mM potassium citrate) on the kinetic parameters (K(p1) V(m)) and on the stability of the photosynthetic activity of immobilized chloroplast membranes has been studied. The results show similarities in behavior of the two supports studied in that, for both, a high concentration of salt (citrate) increases the apparent affinity for ferricyanide and allows a better transformation of this electron acceptor in CSTR experiments.