Polyphenol pathway pathways, microorganisms

Figure 1. Schematic outline of various products and associated enzymes from the shikimate and phenolic pathways in plants (and some microorganisms). Enzymes (1) 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase (2) 5-dehydroquinate synthase (3) shikimate dehydrogenase (4) shikimate kinase (5) 5-enol-pyruvylshikimate-3-phosphate synthase (6) chorismate synthase (7) chorismate mutase (8) prephenate dehydrogenase (9) tyrosine aminotransferase (10) prephenate dehydratase (11) phenylalanine aminotransferase (12) anthranilate synthase (13) tryptophan synthase (14) phenylalanine ammonia-lyase (15) tyrosine ammonia-lyase and (16) polyphenol oxidase. (From ACS Symposium Series No. 181, 1982) (62).

Monophenol oxidase catalyzes the hydroxylation of monophenols to o-diphenols (Figure 11.1). The enzyme is referred to as tyrosinase in animals, since L-tyrosine is the major monophenolic substrate [37], In mammals, L-tyrosine is the initial substrate in the pathway leading to the final products of black-brown eumelanins, red-yellow pheomelanins, or a mixture of pheomelanins and eumelanins. In plants, the enzyme is sometimes referred to as cresolase owing to the ability of the enzyme to utilize the monophenolic substrate, cresol. In microorganisms and plants, a large number of structurally different monophenols, diphenols, and polyphenols serve as substrates for tyrosinase. As many plants are rich in polyphenols, the name PPO has been frequently used for this enzyme [38]. 

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