Tyrosinase copper content

Mutant tyrosinase Copper content (mole/mol subunit)... 

The activation of protyrosinase expressed in E. coli was accomplished by incubation with an acidic buffer at ph 3.0 for 20 min. The copper contents of wild-type and mutant protyrosinases are shown in parentheses the values without parentheses show the copper content of wild-type and mutant tyrosinase after acid activation. Abbreviation PCMB, p-chloromercuribenzoate. 

Table 23. Atomic absorption spectrophotometric determination of copper content for wild-type and mutant tyrosinases from A. oryzae expressed in E. coli...

Copper is present in a number of mammalian proteins and the characteristics of these have been summarized by Scheinberg and Sternlieb [3]. Amongst the copper proteins identified in man, but of unknown function, are cerebro-cuprein I, a protein extracted from normal human brain by Porter and Ainsworth [4], liver copper-protein [5], and erythrocuprein [6]. Tyrosinase, a protein of 0.25% copper content is to be found wherever melanin is present in the body, it catalyses the oxidation of tyrosine to dopa and accelerates the conversion of dopa to dopa quinone, the initicJ stages in the conversion of tyrosine to melanin. Lack of this enzyme is not, however, associated with deficient production of pressor amines, another pathway being present in the adreneil gletnd for the hydroxylation of tyrosine [7]. 

The evidence at present available suggests that the formation of no copper-protein other than caeruloplasmin is disturbed in Wilson s disease. An abnormality of cytochrome oxidase itself would surely be incompatible with life, tyrosinase also does not appear to be abnormal since widespread disturbances of pigmentation are rare indeed [73]. I have seen abnormal skin pigmentation only once in over 70 cases, this was clearly melanin deposited at the site of purpuric haemorrhages on the dorsum of the feet and ankles. Neither have there been any reports of abnormal pigmentary deposits in the brain. The copper content of hair and nails is also normal [74, 75, 76]. 

Another problem to be elucidated is the role of copper in cytochrome a. In the known copper enzymes such as tyrosinase and laccase, copper is an important component of the prosthetic group, but is released from the protein moiety by dialysis against potassium cyanide. In the case of cytochrome a, however, the mode of combination of copper must be different, since very little copper is released from the protein moiety by dialysis. The best known method of releasing the copper is by acid treatment. The role of copper in the electron trasnferring system is still obscure, though Cohen and Elvehjem (1934), Yoshikawa (1937), Schultze (1939, 1941), Gallagher et al. (1956), and Gubler et al. (1957) observed, from dietary experiments, that copper-deficient tissues and yeast have a low cytochrome oxidase activity and a decreased content of hemin a. 

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