Mushrooms enzyme characteristics

Mushrooms have been investigated with especial reference to shiitake, Lentinus edodes, the flavorful fungus widely used in Chinese and Japanese dishes. While the umami taste is attributed to guanylic acid, lentinic acid 14 (Scheme 6) is converted to lenthionine, 1,2,3,5,6-pentathiacycloheptane 15, a compound with the characteristic shiitake flavor. This complex reaction requires a C-S lyase enzyme.30 Other important flavor compounds are 1,2,4,6-tetrathiacycloheptane 16 (Scheme 6) and 1,2,3,4,5,6-hexathiacycloheptane (not shown). 

Lenthionine has the characteristic shiitake flavor. It is formed from the precursor, lentinic acid 14 by complex reactions involving a C-S lyase enzyme.30 Cyclic polysulfides occur in other Basidiomycete mushrooms (Genus Micromp-hale and Colly bid), in some red alga, and in seeds of Parkia speciosa. The latter contain lenthionine and 1,2,4-trithiolane (1,2,4-trithiacyclopentane) 17 as well as compounds with 4, 5, or 6 sulfur atoms.31 These seeds are valued in Indonesia for a unique, onion-like odor. Djenkolic acid and dichrostachinic acid S -[(2-carboxy-2-hydroxyethylsulfonyl)-methyl]cysteine are converted by a C-S lyase enzyme to cyclic polysulfides djenkolic acid yields 1,2,4-trithiolane and 1,2,4,6-tetrathiepane the latter is also formed from dichrostachinic acid.32... 

Many physical characteristics have been determined for the mushroom tyrosinases. These include diffusion coefficients, sedimentation coefficients, frictional ratios, Stoke s radii, isoelectric points, and apparent molecular weights (17-20). Recent evidence suggests that tyrosinase is composed of two heavy chain components (H) of approximately 43-45 kd each and two light chain components (L) of approximately 13 kd each (18-20). The heavy chains contain the catalytic sites. Podila and Flurkey (21) have suggested that the heavy chains were synthesized as smaller molecular weight precursors to the native enzyme. Different isoenzyme forms of tyrosinase apparently contain different H chains (7,17). No role for the L chain subunits have been reported. 

The characteristics of a rennet, however, depend on other conditions than those which could result from its habitat. Thus it is that Gerber, in a comparative study of rennet enzymes of a parasitic mushroom, Plerotus ostreaius, and of the plant on which it grows, Broussonetia papyrifera, found that they are very different. The rennet of the mushroom is very calciphile, very oxyphile, exceedingly sensitive to alkalis, and little resistant to heat that of the white mulberry, on the contrary, is moderately calciphile, moderately oxyphile, little sensitive to alkalis, and very resistant to heat. 

While k Inhibition is characteristic of PPO reactions, the mechanism is poorly understood. Wood and Ingraham (1965) found that mushroom PPO was covalently labeled with when it was incubated with 1- C phenol in the presence of 02 They proposed that a nucleophilic group at or near the active site of PPO reacted with the benzoquinone, via a Michael-type addition, to form an inactive enzyme derivative (Eqn. 4). 

Oxidations now known to be catalyzed by copper-containing enzymes were noticed over a century ago, when Schoenbein observed that oxidation of natural substrates resulted in pigment formation in mushrooms. Individual enzymes were gradually identified laccase by Yoshida in 1883 and tyrosinase by Bertrand in 1896. However, it was not imtil potato polyphenol oxidase was isolated in 1937 by Kubowitz that the role of copper was defined. The family of copper oxidases includes a number of enzymes of both plant and animal origin that may very probably be found to react through similar mechanisms, but which exhibit a number of individual characteristics. The enzymes to be described in this section include potato phenol oxidase, mushroom polyphenol oxidase (tyrosinase), laccase, mammalian and insect tyrosinase, and ascorbic acid oxidase. Each of these differs in certain respects from the others, and undoubtedly other related enzymes will be described from other sources that resemble these, but also display individualities. In these cases, identities in nomenclature must not be extended to imply identities in enzyme structure or activity. 

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