Proteins catalytic wave

Fe 2S], a [4Fe-4S] and a [3Fe-4S] center. The enzyme catalyzes the reversible redox conversion of succinate to fumarate. Voltammetry of the enzyme on PGE electrodes in the presence of fumarate shows a catalytic wave for the reduction of fumarate to succinate (much more current than could be accounted for by the stoichiometric reduction of the protein active sites). Typical catalytic waves have a sigmoidal shape at a rotating disk electrode, but in the case of succinate dehydrogenase the catalytic wave shows a definite peak. This window of optimal potential for electrocatalysis seems to be a consequence of having multiple redox sites within the enzyme. Similar results were obtained with DMSO reductase, which contains a Mo-bis(pterin) active site and four [4Fe 4S] centers. 

Catalytic waves in cobalt solutions. Compounds containing sulphydryl or disulphide groups give two different types of catalytic waves in buffered ammoniacal solutions of cobalt, which are very often named Brdicka catalytic waves. The simple compounds of a low molecular weight (e.g., cystine, cysteine) produce a characteristic round maximum, whereas more complicated compounds such as proteins give a typical double-wave [3,127-131]. 

Brdidka catalytic processes are strongly influenced by the concentration of ammonia and ammonium ions. Any change in their concentration ratio brings a shift in the dissociation equilibria of SH-compounds and their complexes. In excess of ammonia, the coalescence of the protein double-wave occurs, giving a single wave and a considerable increase in the single wave appears as compared to the double wave. 

In such a manner, the activity of different proteolytic enzymes has been estimated. Since the products of proteolytic cleavage can exhibit higher catalytic waves than those of the native proteins, the proteolytic effect can be investigated polarographically. Larger protein molecules can be precipitated with sulphosalicyclic acid. The polarographic analysis of these filtrates corresponds to the content of proteolytic products mainly. 

Proteolysis. The polarographic proof of proteolysis and the estimation of some proteolytic enzymes by means of the increase of the polarographic activity of hydrolysed proteins are described on p. 267. In this part, we should mention another method of following the proteolytic activity. Some polypeptides yield high polarographic catalytic waves in the Brdicka cobalt(III) solution (see p. 265). However, the products of their hydrolysis are polarographically much less active in cobalt (III) solution (see p. 265). In such a manner, the influence of serum of pregnant women on the hydrolysis of protein pituitary extract and on oxytocin and vasopressin was measured [178,179]. 

Kuznetsov studied Brdicka catalytic waves for several nonheme proteins and proposed that complete unfolding accompanied adsorption of these biological molecules. Cytochrome c gave rise to weak Brdicka currents, probably as a consequence of having only three hidden sulfur atoms per molecule. Senda et have recently stated that cytochrome c Brdicka... 

The fact that proteins, in contrast to free cystine and cysteine, are capable of producing a catalytic wave even in solutions of complex trivalent cobalt ions may be explained only if we assume that cobalt is probably capable of entering with sufficient velocity into a complex with proteins, which in turn conditions the catalytic reaction, whereas with free cysteine cobalt reacts relatively more slowly. This explanation is supported by the fact that if the concentration of free cystine is substantially increased, a catalytic wave can also be produced in a solution containing Co (23). Thus the use of the latter solution in polarographic examinations of proteins and high-molecular polypeptides helps eliminate the undesirable influence of free cystine, cysteine, and their low-molecular polypeptides. 

Proteins may 3rield also reduction waves, provided that they contain disulfidic groups, as, for example, serum albumin or insulin do. Such a reduction wave, however, is very low, usually 200 to 400 times lower than the catalytic waves (40). 

Substances showing catalytic waves in ammoniacal cobalt or nickel solutions< > must fulfil another condition beside the two conditions mentioned above the substance has to form a complex-compound with cobalt and other components of the solution. Moreover, the acid properties of this complex and its adsorbability also seem to be of importance. The substances showing a catalytic effect of this type usually contain at least an atom of sulphur in their molecule (e.g. cysteine, dithiopyrimidine or proteins). Whether or not the presence of sulphur in the catalytically active molecule is a sufficient condition has yet to be decided. It was shown that e.g. gelatin or casein containing little or no sulphur atoms do not produce any catalytic wave of this type. Similarly, in the series of hydantoin, thiohydantoin and dithiohydantoin as well as pyrimidine, thiopyrimidine, and dithiopyrimidine, the catalytic effect was only observed for the thioderivative and it increased with the number of sulphur atoms in the molecule. 

Pollen allergens can be determined( > from the catalytic wave which these proteins give in ammoniacal cobaltic solutions. To express the content of pollen allergens in different preparations it is necessary to choose, as a standard, the allergen from one plant. 

Brdiika catalytic wave. The Brdicka protein reaction is perhaps one of the most important among the polarographic methods used... 

All proteins yield catalytic hydrogen waves ( presodium waves ) at the negative end of polarograms by lowering the hydrogen overvoltage as discovered by Heyrovsky and Babicka in 1939. Moreover, in 1933 Brdicka introduced the catalytic double waves in the presence of cobalt ions which... 

Figure 6. Scheme of relative wave heights (hr) versus the uv dose for A serum albumin R RNase. K catalytic presodium wave (peptide wave), M damping curve for O2 maximum, Pj+2-both Brdicka protein waves, Pj first Brdicka protein wave. 

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