On the composition of tyrosinase from two 



enzymes. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. XV, 1913, p. 932 937. Verscheen onder den titel Over de samenstelling 

 der tyrosinase uit twee enzymen in Verslagen Kon. Akademie van Wetenschappen, 

 Wis-en Natuurk. Afd., Amsterdam, Deel XXI. 1913, biz. 923930. 



The product of the action of tyrosinase on tyrosin is commonly called melanin, 

 whose colour may be jet black, but takes all shades between light brown, 

 pure red, brownish red, sepia and black in experimental conditions. These pigments 

 are of uncommon stability and resist even heating with strong alkalies and sulfuric 

 acid, whereby the black runs somewhat into brown but in chief remains unchanged. 

 Even when boiled with nitric acid the melanin remains almost unchanged. It is 

 accepted that the pigment of the hair and hide of higher animals is associated with 

 these substances and is derived from tyrosin. 



Melanin formation by symbiose of an Actinomyces zvith a bacterium. 



On a culture plate of the composition: distilled water, 2% agar, 0.1% tyrosin 

 (dissolved in a few drops natriumcarbonate) and 0.02% K 2 HPO 4 , on which some 

 centigrams garden soil are sown and which is kept at 30 C., hundreds or thousands 

 of little sods of Actinomyces (Streptothri.v) will develop after two or three days. 

 The tyrosin serves at the same time as source of carbon and of nitrogen. But the 

 agar itself also is attacked by these microbes, although with difficulty, and used as 

 food. This is not surprising as many Actinomyces-species can even live on cellulose 

 as source of carbon. 



The common bacteria of the soil develop not or hardly on the tyrosin plate and 

 cannot in the given circumstances compete with the slowly growing Actinomyces as 

 they do on better media, e.g. on broth agar, where Actinomyces never occurs when 

 bacteria are present. 



As the delicate threads of this genus enter deep into the agar, the plates may be 

 freed by washing from the bacterial colonies and the adhering soil ; then the Actino- 

 myces sods can be easily counted. In humus and humus containing soil their number is 

 amazing. When they can freely multiply on plates which are poor in food their 

 growth is unlimited and they produce sods of great extension, even of one or more 

 decimeters in surface, commonly producing very fine mycelial-rings, which by turns 

 bear spores or not. These rings are independent of light and suggest a periodicity in 

 the nutrition not yet fully explained. 



