E. H. NEWCOMB 4^5 



homogenates of either young or old tissue since, when either ascorbic 

 acid or /7-phenylenediamine was used as a substrate, the addition of 

 cytochrome c did not result in an increased oxygen consumption. On 

 the other hand, ascorbic acid oxidase and tyrosinase activity were found 

 in normal and gall material of all ages. The presence of ascorbic acid 

 oxidase was shown by the vigorous oxygen consumption supported by 

 ascorbic acid. While laccase can also oxidize ascorbic acid, the inactivity 

 of the homogenates toward hydroquinone indicated its absence. Tyro- 

 sinase activity was shown by the oxygen consumption on a variety of 

 poly- and monophenols known to be attacked by this enzyme. Catechol- 

 ase, while not attacking monophenols, can oxidize the polyphenols 

 employed, but its presence in any considerable amount seems unlikely 

 because of the agreement between trends in rates of mono- and poly- 

 phenol oxidation for material of different ages (Table 2). 



When gall and normal leaf tissues are compared, the trends in levels of 

 ascorbic acid oxidase and tyrosinase activity as the tissues mature are 

 striking (Table 2). Ascorbic acid oxidase activity is greater on a dry 

 weight basis in both young and old galls than in leaves. As both gall 

 and normal tissues age the activity decreases considerably. 



Tyrosinase activity decreases greatly during the maturation of normal 

 leaf tissue. But whereas tyrosinase activity in young galls is only about 

 one-half that of young leaves, it is approximately doubled in old galls, 

 and exceeds that of mature leaves several fold. The significance of this 

 increase in the amount of an enzyme acting on polyphenolic compounds 

 which takes place as the galls age is not yet clear. The fact may be 

 recalled, however, that such compounds are capable of functioning as 

 H-carriers with tyrosinase. Whether one or both of these oxidases par- 

 ticipate as terminal oxidases in the respiration of these tissues is not 

 certain. Both are copper-containing enzymes sensitive to such poisons as 

 8-hydroxyquinoline and allylthiourea. Inhibition of leaf respiration by 

 these poisons is only partial (about 30 per cent for 5 x iq-^ M allylthi- 

 ourea for both young and old tissue), while the gall respiration appears to 

 be insensitive to both poisons. 



The disparity in the trends which occur in the activity of the two 

 oxidases as the gall and normal tissues mature suggests the possibility 

 that the two enzymes are not associated in the same types of cytoplasmic 

 particles and that there is a differential rate of multiplication of the latter. 

 Comparison of the types and numbers of plastids and mitochondria and 



