46 THE PLANT CELL WALL 



feic, ferulic, and phenylpyruvic acids; and glucosides such as 

 coniferin, syringin, and glucovanillin. 



Enzymological studies have focused attention upon phenol- 

 dehydrogenase mixtures from the conifer Araucaria and from 

 common mushrooms; laccases from mushrooms, and the Japanese 

 lac tree; and peroxidases from a great variety of tissues. The lac- 

 cases and peroxidases are associated with the terminal steps in 

 lignin synthesis, the oxidative polymerization reactions themselves. 

 These reactions correspond to the general formulation: 



laccase or 



c 6 -c 3 (-c 6 -c 3 -) n 



phenylpropane peroxidase lignin 



monomer polymer 



This formulation is too general, however, to provide an accurate 

 picture of the transformations involved. Thus, a number of sup- 

 porting or preparative reactions and enzymes must be taken into 

 consideration. Among these reactions are: 



p-glucosidase 



(a) Glucoside hydrolysis, as in coniferin ~» coniferyl 



alcohol + glucose. 



transaminase 



(b) Deamination as in tyrosine +oc-ketoglutarate ► 



pyridoxal-5- 



phosphate 

 /?-hydroxyphenylpyruvate+glutamate, and 



amino acid oxidase 



tyrosine — » p-hydroxyphenylpyruvatc. 



FAD 



(c) Hydroxylation as in 



hydroxylase 

 phenylalanine -- » tyrosine 



tyrosinase 

 tyrosine — ► DOPA. 



