The formerly described Microspira tyrosinatica (I.e.) living in the sea and in 

 sewagewater, oxidises tyrosin directly to melanin without intervention of any other 

 organism. That this is done here also by a vigorously active tyrosinase is easily 

 shown with the form living in the sea, the bacterium, when killed by chloroform, 

 being still able to cause the melanin reaction. I think it is proved now, that also in 

 this case the tyrosinase consists of two enzymes, as it is possible with Microspira 

 to oxidise the homogentisinic acid to a dark pigment. 



In order to ascertain how in this respect the tyrosinase of the higher plants 

 behaves, I took strong tyrosinase preparations derived from the potato, the beetroot 

 and latex of Euphorbia Lathyris 1 ) which quickly colour tyrosin solutions deep 

 black, and made them act on homogentisinic acid salts. The latex of Euphorbia 

 Lathyris is extremely fit for these experiments as it can always be made to drip 

 from the living plant, which supports our winters very well in the garden. A single 

 drop on an agar-tyrosin plate at from 30 to 50 C. forms deep black melain spots 

 after a few hours already. But homogentisinic acid can also be oxidised with great 

 velocity. For this experiment I used an agarplate of this compositon: water, 2% 

 agar, 0,5% natrium homogentisinate, 0,02% NHC1 and 0,02% K 2 HPO.j. 



On this plate drops of the latex were put and besides streaks were made of 

 Actlnomyces and the symbiotic bacterium. After some hours, at 30 C., dark 

 brownish black fields appeard, evidently more readily formed than the black fields 

 from the tyrosin. 



After about 24 hours Actinomyces also began to grow but no pigment at all 

 appeared, as was to be expected. The symbiotic bacterium did not develop under 

 the^e conditions. But some broth being added to a like medium the bacterium could 

 grow and oxidised the homogentisinic salt to melanin. So it is certain that also the 

 tyrosinase of Euphorbia Lathyris must be a mixture of two oxidising enzymes; one 

 of these, which may preserve the name of tyrosinase, produces homogentisinic acid 

 from tyrosin, the other, homogentisinase, forms melanin from the acid, and 

 corresponds with the oxidase of the symbiotic bacterium. This enzyme requires no 

 special name as homogentinase and laccase are probably identic. 



Although the two enzymes theory* of the tyrosinase may be considered as 

 confirmed by what precedes, still it should be called to mind that, when a method of 

 experimenting is used somewhat deviating from the described the above result with 

 Euphorbia Latyris is not obtained. Such is, namely, the case when the milky juice 

 of the plant is put on agarplates with homogentisinic acid salt, with addition of broth 

 for the bacteria. Then the surprising fact occurs that the bacterium is active but 

 the latex is not. Whereon this difference reposes is no clear. 



Finally it may be mentioned that the existence of two enzymes in the tyrosinase 

 of the beetroot was already made probable by P. C. van der W o 1 k (Recherches 

 au sujet de certains processes enzymatiques chez Beta vulgar is, Nimegue 1912.) 



*) The latex of Euphorbia palustris, E. Peplus, E. helioscopia, E. Mysinitis, contain 

 no tyrosinase. 



