54 OXIDATION-REDUCTION POTENTIALS 



The need of Hasmophilus influenzce for protoporphyrin for growth (the X factor, 

 of Lwoff and Lwoff) depends upon the inabihty of the organisms to synthesise the 

 necessary cytochrome etc., enzymes without the porphyrin into which iron may be 

 incorporated ; other porphyrins could not replace protoporphyrin (Granick and 

 Gilder, 1946.) 



COPPER PROTEIN OXIDASES 



Several plant proteins containing copper have been found to function as oxidases : 

 they include tyrosinase, laccase and ascorbic acid oxidase. In general the proteins 

 are blue and catalyse the direct oxidation of their substrates by molecular oxygen 

 but not by methylene blue and other dyes under anaerobic conditions and no hydro- 

 gen peroxide formation has been detected as has been done in the case of other 

 dehydrogenases. Cyanide inhibits their action. (For a review see Dawson and 

 Mallette, 1945.) 



Laccase, obtained from the latex of lacquer trees, oxidases polyhydric phenols 

 e.g., hydroquinone and guaiacum (Keilin and Mann, 1940 ; Kubowdtz, 1937, 1938.) 

 Tyrosinase occurs in mushrooms, potatoes, tea and tobacco as well as in insects and 

 invertebrates. Under aerobic conditions it oxidises monophenols and 0-dihydric 

 phenols, among the substrates oxidised being phenol, p-cresol, catechol, tyrosine and 

 adrenaline (Kubowitz, 1937 ; Raper, 1928 ; Keilin and Mann, 1938 ; Nelson and 

 Dawson, 1944), and the darkening of injured tissues has been ascribed to tyrosinase 

 activity. The meal-worm is a useful source of the pro-enzyme. Figge (1940) finds 

 that melanin production by tyrosinase is subject to an oxidation-reduction potential 

 optimum range for maximum activity. 



Ascorbic acid oxidase oxidises ascorbic acid and is found in cabbages and many 

 other plants. (Szent-Gyorgi ; Zilva ; Barron, de Meio and Klemperer, 1936 ; Stotz ; 

 Meikeljohn and Stewart, 1941.) 



Hsemocyanin is a complex copper protein occuring in the blood of invertebrates 

 such as crabs and snails ; it is blue when oxygenated and nearly colourless when 

 de-oxygenated and it plays a role in respiration similar to that of haemoglobin. 

 Hsemocuprein is a blue copper protein found in mammalian blood, containing 0-34% 

 of copper with a molecular weight of 35,000 having two atoms of copper in the 

 protein molecule. 



The dropping mercury electrode has been used (Ames and Dawson, 1945) for 

 the determination of copper in copper proteins. 



COBALT COMPLEXES— ANTI-PERNICIOUS ANAEMIA FACTOR 



The anti-pernicious anaemia factor of liver which is required, in addition to folic 

 acid, for prevention of sj)inal degeneration has been isolated and found to be a deep 

 red cobalt complex (Rickes et al, 1948, Smith and Parker, 1948) which is active in 

 minute doses. 



The power of cobalt complexes to unite reversibly with oxygen has been studied 

 by Calvin and Barkelew (1946). The observation of Burk, Hearon, Caroline and 

 Schade (1946) that cobalt inhibits the growth and respiration of micro-organisms, 

 tissues and tumours led to the investigation of the chelate cobalt complexes of histi- 

 dine. Purple complexes of trivalent cobalt were observed by Laland and Closs (1945) 

 in the case of all amino acids except tryptophane, and with protein hydroly sates. 

 The casein cobalt complex was not attacked by papain but was partly digested by 



