Biological substances, reactions

There is quite a large body of literature on films of biological substances and related model compounds, much of it made possible by the sophisticated microscopic techniques discussed in Section IV-3E. There is considerable interest in biomembranes and how they can be modeled by lipid monolayers [35]. In this section we briefly discuss lipid monolayers, lipolytic enzyme reactions, and model systems for studies of biological recognition. The related subjects of membranes and vesicles are covered in the following section. 

Special reactors are required to conduct biochemical reactions for the transformation and production of chemical and biological substances involving the use of biocatalysts (enzymes, immobilised enzymes, microorganisms, plant and animal cells). These bioreactors have to be designed so that the enzymes or living organisms can be used under defined, optimal conditions. The bioreactors which are mainly used on laboratory scale and industrially are roller bottles, shake flasks, stirred tanks and bubble columns (see Table 1). 

EBERT AND SWALLOW Reactions with Biological Substances... 

Among other reactions of the hydrated electron may be mentioned the reaction with methylene blue. Methylene blue may be regarded as the prototype of easily reducible biological substances such as NAD, cytochrome-c, etc. The preliminary value for the rate constant for reaction with the hydrated electron (5) has now been shown to be too high, and the more reasonable value of 2.5 X 1010 M-1 sec.-1 has been obtained (19). It is thus no longer necessary to attribute special properties to methylene blue. 

Enzyme-based biosensors are very suitable for the antioxidant status evaluation, since they show excellent selectivity for biological substances and can directly determine and/or monitor antioxidant compounds in a complex media such as biological or vegetable samples without needing a prior separation step. During the course of the catalytic reaction on the electroactive substrates, the current produced at an applied potential is related to the concentration of a specific biomarker, for which the biosensor is selective. HRP-based biosensors for antioxidant status evaluation have been applied in the detection of superoxide radical [119], nitric oxide [120], glutathione [119, 121], uric acid [122, 123], and phenolic compounds [124—126],... 

The majority of the industrially applied biotechnical processes for the generation of flavour preparations relies on reactions with isolated enzymes and enzyme complexes. The basic principle of enzymatic reactions is mostly hydrolytic decomposition or transformation of the most important biological substance categories like proteins, carbohydrates, lipids and acids. 

Though a biological recognihon reaction is typically very selective, interferences may occur due to substances other than the analyte of interest. Such interferences can be converted by the biorecognition element or at the transducer surface and... 

Enzymes are expensive and difficult to obtain in pure form. Only recently have enzymes, often in immobilized form, been increasingly used for reactions of non-biological substances. With the increasing importance of biotechnological processes, enzymes will also grow in importance. 

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