3 io THE OXYDASES 



such circumstances, In addition to laccol, other polyatomic phenols (pyrogallol, 

 hydroquinone, <fec.) and their acid derivatives (e.g. gallic acid and tannin) are 

 quickly oxidised by laccase in presence of air. According to the further dis- 

 coveries of BERTRAND (III.), tne polyphenols containing at least two groups of 

 OH or NH., (either in the ortho- or in the para-position) are also easily and 

 readily oxidised by this oxydase. 



This interesting discovery gave an impulse to the elucidation of several other 

 phenomena interesting both to the food-stuff chemist and the agriculturist. It 

 is well known that the freshly broken or cut surfaces of raw apples rapidly 

 become discoloured on exposure to the air, at first turning reddish and then 

 becoming brown. This is the cause of the ugly colour of expressed apple-must. 

 Housewives skilled in cookery are aware that this alteration of colour does not 

 ensue if the cellular structure of this fruit is preserved unbroken until after the 

 apple has been boiled. L. LINDET (I.) in 1893 explained this discoloration as 

 resulting from the action of an enzyme, to which he subsequently gave the name 

 of laccase without, however, implying the identity of this with the oxydase of 

 the lac-tree. The name of malase would probably be more suitable for this apple 

 enzyme. In the case of apple-juice also, oxygen is carried by the enzyme to the 

 tannin, and thus dark-coloured oxy-compounds are produced, which are pre- 

 cipitated on the cell walls as a fast, permanent dye. The spotting of sound 

 apples under the rind, the so-called brown spotting, is explainable in the same 

 manner. So long as the structure of the cell remains perfectly intact, the 

 atmospheric oxygen cannot obtain access to the enzyme (in the plasma) or to the 

 tannin. As soon, however, as by mechanical action (e.g. the dropping of the 

 apple from the tree, pressure in packing or transit, &c.) any of the cells become 

 ruptured, then an opportunity is afforded the oxygen to act on the now exposed 

 constituents of the plasma. If the rind of the fruit remains uninjured, the air 

 gains admission to the interior merely through the intracellular spaces alone, and, 

 in such event, will produce only a faint reaction and slight discoloration. 

 Whether, as assumed by Lindet, the enzyme and tannin are contained in separate 

 cells (i.e. distinct from each other), is a question still requiring more accurate 

 research on the part of the botanist to decide. 



The darkening of beet-juice, or the rapid discoloration of the fresh slices of 

 beet in the sugar-works evidenced even when cutting-tools devoid of iron are 

 employed, is equally attributable to the action of an oxydase present in the sugar- 

 beet. This was discovered by G. BERTRAND (IV.)> and received the name of 

 Tyrosinase, because it carries atmospheric oxygen to the tyrosine well known 

 to be abundantly present in the cells of the sugar-beet and thus produces the 

 discoloration in question. On the other hand, laccase has no effect on the said 

 amido-compound. Apart from this property, tyrosinase is also characterised by 

 its greater susceptibility both to heat and chemical influences. It occurs in other 

 plants, e.g. the bulbs of the dahlia (Dahlia variabilis). According to the 

 researches of G. BERTRAND (V.), oxidising enzymes are also found in other 

 plants, e.g. in the carrot ; the tubers of the potato (which, as is well known, 

 rapidly become discoloured when cut in an uncooked state) ; in the pear, quince, 

 and chestnut ; in the sprouts of asparagus, clover, lucerne, and rye-grass ; in 

 the leaves of the potato, sugar-beet, <tc. For detecting this class of enzymes 

 Bertrand recommends the employment of guaiacum tincture, which produces 

 therewith a blue coloration when dabbed or poured on to the cut surface or juice 

 under examination. To isolate these enzymes the plant juice is mixed with 

 alcohol, the resulting precipitate being dissolved in a little water and filtered. 

 On pouring the filtrate into five volumes of alcohol, a precipitate consisting of the 

 desired enzyme will be formed. 



The so-called rusting or tarnishing of many of the agarics, i.e. the rapid 





