160 E. R. Way good and G. A. Maclachlan 



of Mn+3 from Mn^^. Manganiversene is rapidly reduced by catechol, 

 and pre-incubation of catechol with manganiversene or even manga- 

 nous ions also destroys its inhibitory effect, presumably by promoting 

 oxidation of catechol. Tiie evolution of carbon dioxide is also in- 

 hibited by catechol, antl this lends support to the hypothesis that 

 catechol exerts its inhibition in the initiation reactions or in the first 

 step of propagation in which reactions manganic ions are involved. 

 Nevertheless, the possibility cannot be excluded that the inhibition 

 by catechol is caused by stabilization of a cofactor or skatole radical 

 which in turn results in its destruction. The fact that the catechol- 

 induced lag period varies in length with the cofactor used (Table 1) 

 suggests that the cofactors or their radicals may compete at different 

 rates for catechol, but this could also be interpreted in terms of 

 their varying reactivity in manganigenesis. If, on the other hand, 

 catechol were involved in a reaction with skatole radicals which are 

 involved solely in propagation, it would be more likely to exert a 

 retarding effect rather than an inhibition at least at lower concen- 

 trations. The most probable explanation is that catechol reacts with 

 manganic ions produced during the initiation reactions and tem- 

 porarily blocks the decarboxylation of lAA. The same argument 

 would apply to pyrogallol, ascorbic acid, and possibly rutin. 



Mechanism of Retardation by Chain-transferring Agents 



The retarding effects of hydroqtiinone or its oxidation product, 

 p-benzoquinone, riboflavin, or its phosphate, and scopoletin persisted 

 even though several himdred moles of oxygen were consimied per 

 mole of retarder present. This persistence indicates that although 

 these retarders are changed by interfering in the reaction sequence 

 they must also be reformed probably by participating in reversible 

 redox system, a property that they wotdd all share. 



Hydroquinone p-benzoquinone. Systems containing hydroqtiinone 

 differed from the others in the lower final equilibrium attained 

 (Figure 1). This was due to a decline in lAA concentration and indi- 

 cates a side reaction of the retarder with lAA. The oxygen uptake 

 of systems containing either hydroquinone or p-benzoquinone dif- 

 fered only in the initial velocity, which was always slightly greater 

 with the latter. Thereafter the progress curves continued parallel 

 as would be expected if a steady state equilibrium was established 

 between the oxidized and reduced forms. 



Since hydroquinone rapidly reduces manganiversene it is prob- 

 able that it competes successfully with lAA for Mn^"^ in tlie same 

 way as catechol, but differs in that the oxidation product p-quinone 

 is not without effect on the system, but enters into another reaction 



