Isothermal and non-isothermal bioreactors in the detoxification of waste waters polluted by aromatic compounds by means of immobilised laccase from Rhus vernicifera

Laccase from Rhus vernicifera was immobilised on a nylon membrane chemically grafted with glycidyl methacrylate (GMA). Hexamethylenediamine (HMDA) and glutaraldehyde (GLU) were used as spacer and bifunctional coupling agent, respectively. Quinol was used as substrate.

To know how the immobilisation procedures affected the enzyme reaction rate the catalytic behaviour of soluble and insoluble laccase was studied under isothermal conditions as a function of pH, temperature and substrate concentration. From these studies, two main singularities emerged from the experimental data: (i) the narrower pH-activity profile of the insoluble enzyme in comparison to that of the soluble counterpart; (ii) the increase of the affinity of the immobilised enzyme for its substrate.

The behaviour of the catalytic membrane was also studied in a non-isothermal bioreactor as a function of substrate concentration and size of the applied transmembrane temperature difference. It was found that, under non-isothermal conditions and keeping constant the average temperature of the bioreactor, the enzyme reaction rate linearly increases with the increase of the temperature difference. These results have been discussed in the frame of reference of the process of thermodialysis driving thermodiffusive transmembrane substrate fluxes, which add to the diffusive ones.

The advantages of the catalytic process carried out under non-isothermal conditions have been thrown in relief through the evaluation of the reduction of the production times and of the percentage increases of the enzyme activity.     

A simple and sensitive method for determination of human urinary kallikrein activity (kininogenase activity), using human low molecular weight kininogen

Human low molecular weight kininogen was partially purified and applied to the measurement of human glandular kallikrein as a substrate. The prepared human low molecular weight kininogen did not contain any significant amounts of kinin generating or destroying enzymes. When ethanol was added to the assay tube to stop the enzyme reaction, the substrate was almost completely removed from the incubation solution. Moreover, less than 1.25% ethanol had no effect on the kinin radioimmunoassay. These data suggest that the measurement of generated kinin can be done directly after the addition of ethanol. In this assay system, control tubes were unnecessary since the small volume of the urine samples (0.5 to 2.0 nl) contained negligible amounts of endogenous kinin. In a comparison of the availability as a substrate for human urinary kallikrein among human, dog and bovine low molecular weight kininogens, the enzyme activity was 5 or 100 times as high in the human substrate as in the dog and bovine substrates, suggesting that a human substrate is best for the human enzyme. A significant correlation was found between our previous method using bovine substrate and this method for human urinary kallikrein activity. In both methods, urinary kallikrein excretions were significantly lower in patients with essential hypertension and higher in those with primary aldosteronism, respectively. This simple, specific and sensitive kininogenase assay system seems to be very useful for investigating the physiological or pathophysiological role of the renal kallikrein-kinin system in hypertensive and renal diseases.