PSII Activity after Immobilization

The PSII complex is known to be particularly sensitive to many substances and its activity is studied firstly. Different methods were used to detect the activity of PSII aftet immobilization of photosynthetic material (Fig. 2). There is no relation between the method of immobilization and the measurement technique of the photosynthetic activity. 

The measurement of oxygen evolution using a Clark-type oxygen electrode is a standard procedure in the field of photosynthesis research. The measure is simple and the oxygen electrode constitutes an interesting method to evaluate the photosynthetic activity. Several types of photosystem II specific artificial electron acceptors can be used as electroactive mediators to maximize the photosynthetic activity. The more used mediator is potassium ferricyanide but this one 

The measurement of the PSII activity can be based on amperometric detection of the reduced form of a specific artificial electron acceptor in an electrochemical cell. The mediator must be present in its oxidized form in the measuring buffer. Under illumination, this artificial electron acceptor is reduced and then reoxidized on the surface of a working electrode. Different mediators were used potassium ferricyanide, parabenzoquinone, duroquinone, 2,6 dimethylbenzoquinone. With whole cells of eukaryotic algae, potassium ferrycianide, methyl-viologen, and DCIP were unable to access the photosynthetic electron transfer chain.  

A special electrochemical cell was often employed to detect the photosynthetic activity of immobilized thylakoids. With this electrochemical micro-cell, it was possible to detect a photocurrent of free or immobilized thylakoid membranes in the absence of exogenous artificial electron acceptor. The photosynthetic origin of the photocurrent was demonstrated by an inhibition in the presence of the photosynthetic inhibitor diuron. The inhibition of the photocurrent by catalase, an enzyme that degrades hydrogen peroxide, demonstrated that dissolved oxygen was involved. The ability of oxygen to act as an electron acceptor for the photosynthesis membrane was initially demonstrated by Mehler. This process, known as pseudocyclic electron transport or Mehler 

Biotechnological Applications of Photosynthetic Proteins Biochip, Biosensors and Biodevices 

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Immobilization Procedure PSII Activity (%) after Immobilization PSII Activity (%) after 400h of Storage ... 

It was observed that the specific activity of PSII of chloroplasts immobilized in DEAE-cellulose was higher than those of the free chloroplats. The activities of PSI and PSII catalyzed by free or immobilized chloroplasts were both insensitive to uncouplers after adsorption indicating that the immobilized chloroplasts had already been uncoupled. 

Examples of PSII activities (oxygen production) after immobilization of thylakoids according to the procedure ate shown in Table 2. As the uncoupling effect of each method varies, an uncoupler (NH4CI) was added to the reaction medium in order to obtain a well defined activity yield. 

Table 2. PSII activity (oxygen production) after immobilization of thylakoirls...

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