Enzyme fruit ripening

KUNTZ M, ROMER s, suiRE c, HUGUENEY p, WEIL j H, scHANTZ R and CAMARA B (1992) Identification of a cDNA for the plastid-located geranylgeranyl pyrophosphate synthase from Capsicum annuum correlative increase in enzyme activity and transcript level during fruit ripening , Plant J, 2, 25-34. 

Bartley, G.E. et ah, A tomato gene expressed during fruit ripening encodes an enzyme of the carotenoid biosynthesis pathway, J. Biol. Chem. 267, 5036, 1992. 

It is not yet known whether the increase of these activities in the course of fruit ripening is due to a direct synthesis of the enzymes, or whether conversion of inactive precursors into the active enzymes is involved. There is also the possibility of (a) an effect of inhibitors present in unripe fruit on the activity of endo-D-galacturonanase, and (b) disappearance of such inhibitors in the course of ripening.184 For pectinesterase, it has been speculated that plants may be able to regulate the activity of this enzyme by metabolic control of the amount and proportion of certain, naturally occurring, fatty acids.82... 

Fruit tissues respond to ethylene by exhibiting increases in the activities of enzymes that catalyze ripening reactions, and in some cases, the increases in enzyme activity probably are the result of de novo synthesis, rather than activation of preexisting enzymes. Other target tissues respond similarly to ethylene. But it is not known whether ethylene acts directly to evoke new enzyme production. Interpretation of results with inhibitors of RNA and protein synthesis is inconclusive, because it could be merely that RNA and protein synthesis are essential to maintain the cells in a state competent to respond to ethylene. Moreover, there are some responses to ethylene, besides fruit ripening, which occur under conditions which apparently do not directly involve RNA and protein synthesis (e.g., membrane permeability changes). It has been proposed that the in vivo ethylene receptor site contains a metal such as copper (34,35). 

We noted earlier in this chapter (Section II.C.3) the pyridoxal-phosphate-linked enzymatic route of synthesis of ACPC (9) from the a-aminobutyryl moiety of S-adenosylmethionine (99). ACPC (9) undergoes further metabolic processing by two distinct fragmentation routes, to a-ketobutyrate (138) and ammonia (equation 21) in bacteria and yeast or to ethylene (139) in fruit and other plant tissues (equation 22) where ethylene (139) is a potent hormone for fruit-ripening or wound-healing The bacterial enzyme, ACPC deaminase is much better characterized and is taken up first. 

Usually, donor and acceptor functions are located at different ring carbon atoms, but there are also examples in which both functions are linked to the same atom. The most prominent compound of this type is 1-aminocyclopropanecarboxylic acid (ACC, 6), a naturally occurring amino acid which is the precursor of the fruit-ripening hormone ethene. In fruit tissues, such as apple tissue, this amino acid is oxidized to ethene, carbon dioxide and hydrogen cyanide by the enzyme ACC oxidase, also known as ethene-forming enzyme (EFE). This reaction has been studied in detail. ... 

Reported results indicate that in fruit ripening and flower senescence, genes of ACC synthase and ACC oxidase are co-ordinately expressed, whereas in vegetative tissues, expression of genes coding for the two enzymes is not necessarily co-ordinated. 

Anthocyanins occur ubiquitously in fruits and confer orange, red, blue, and purple colors of many fruits such as apples and berries. Cyanidin glycosides are the most common anthocyanin in foods. Its content is generally proportional to color intensity and reaches values up to 250 mg/100 g of fresh blackcurrants [30] and 146-2199 mg/100 g fresh black berries [31]. This value increases as the fruit ripens. The anticarcinogenic activity of anthocyanins revealed from in vitro and in vivo studies showed its radical scavenging activity, stimulation of phase II detoxifying enzymes, reduced cell proliferation, inflammation, angiogenesis and invasiveness, and induction of apoptosis and differentiation [32]. 

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