AMINOPHENOLS AND PHENYLENEDIAMINES 585 



Many of the quinones mentioned above in metabolic or antimitotic studies 

 occur naturally. p-Benzoquinone, toluquinone, and the xyloquinones occur 

 in either plants or insects, while the methoxy- and dimethoxy-p-quinones 

 apparently are found in wheat germ. Lawsone (2-hydroxy-l,4-naphthoqui- 

 none) is the dye in henna [Lawsonia alba), lapachol is a yellow pigment 

 in the wood of Tecoma (greenheart) and other trees, lomatiol is a dye ob- 

 tained from the seeds and bark of species of Lomatia, juglone is found in 

 various parts of walnut trees, and phthiocol was originally derived from 

 Mycobacterium tuberculosis. All of these and other quinones are occasionally 

 quite potent inhibitors of metabolism or mitosis. Do they function in any 

 way in the control of metabolism or growth in the microorganisms on 

 plants? Almost nothing is known about this interesting aspect of the prob- 

 lem, but it has been suggested that they may regulate the rate of mitosis in 

 growing tips or participate in oxidation-reduction reactions, for neither 

 of which there is much evidence. In fact, it has been pointed out that cer- 

 tain fungal mutants which do not form a quinone normally present manage 

 to proliferate and survive without difficulty. One might also raise the 

 question as to how tissues which contain inhibitory quinones resist their 

 actions. An important factor here is probably the fact that these quinones 

 occur within the plant cells to a large extent as glycosides and hence are 

 inactive. However, the quinones sometimes occur in a free form and ap- 

 parently in rather high concentrations; e. g., lawsone may be around 1% 

 in henna leaves, lomatiol 3.5% in the fruit and 12% in the seeds of Lomatia, 

 and juglone nearly 8% in the walnut catkin buds. They may not be dis- 

 tributed uniformly and possibly in some instances are mainly outside 

 the cells. 



AMINOPHENOLS AND PHENYLENEDIAMINES 



The ability to form quinonoid structures is also possessed by compounds 

 in which the phenolic hydroxy groups of o- and p-benzohydroquinones are 

 replaced by amino groups, and there is some evidence that these substances 

 often exert metabolic actions similar to those of the quinones and hydro- 

 quinones. Early interest in p-aminophenol stemmed from the fact that 

 it is a major metabolite of certain antipyretics and analgetics, such as 

 acetanilide and acetophenetidin, and was thought by some to be responsible 

 for the pharmacological effects of these drugs, while p-phenylenediamine 

 attracted attention because of its toxic actions when used as a hair dye and 

 industrially in the dyeing of fur and feathers and the vulcanization of rub- 

 ber. Battelli and Stern (1912) demonstrated that j)-phenylenediamine is 

 readily oxidized hy various mammalian tissue preparations, and it has 

 been used by biochemists since that time as a hydrogen donor to the cyto- 

 chrome system and as a cytological stain for oxidases. More recently there 



