Enzymatic Browning and Biochemical Alterations in Black Spots of Pineapple [Ananas comosus (L.) Merr.]

Penicillium funiculosum Thom. was consistently isolated from pineapple-infected fruitlet (black spots). Polyphenol oxidase, peroxidase, and laccase activities were determined in extracts from contiguous and infected fruitlets. Healthy fruitlets showed a rather high level of polyphenol oxidase (optimum pH 7.0), and this activity was tremendously increased (×10) in contiguous infected fruitlets. Furthermore, infected fruitlets also exhibited laccase activity (optimum pH 4.0), while peroxidase was rather constant in both fruitlets. Browning reactions were attributed to qualitative and quantitative modifications of the enzymatic equipment (polyphenol oxidase and laccase) (p<0.0001). In infected fruiltets, sucrose and L-malic acid were present at significantly lower amounts than in healthy ones, likely owing to fungal metabolism (p<0.0001), whereas cell wall material was three times higher, which could be viewed as a defense mechanism to limit expansion of the mycelium. RID= ID= <E5>Correspondence to: </E5>S. Avallone; <E5>email:</E5> avallone&commat;siarc.cnearc.fr Received: 3 September 2002 / Accepted: 25 September 2002     

Enzymatic browning and biochemical alterations in black spots of pineapple [Ananas comosus (L.) Merr.

Penicillium funiculosum Thom. was consistently isolated from pineapple-infected fruitlet (black spots). Polyphenol oxidase, peroxidase, and laccase activities were determined in extracts from contiguous and infected fruitlets. Healthy fruitlets showed a rather high level of polyphenol oxidase (optimum pH 7.0), and this activity was tremendously increased (X 10) in contiguous infected fruitlets. Furthermore, infected fruitlets also exhibited laccase activity (optimum pH 4.0), while peroxidase was rather constant in both fruitlets. Browning reactions were attributed to qualitative and quantitative modifications of the enzymatic equipment (polyphenol oxidase and laccase) (p < 0.0001). In infected fruiltets, sucrose and L-malic acid were present at significantly lower amounts than in healthy ones, likely owing to fungal metabolism (p < 0.0001), whereas cell wall material was three times higher, which could be viewed as a defense mechanism to limit expansion of the mycelium.     

Increased platelet-activating factor-induced periventricular brain microvascular constriction associated with immaturity

Oxidant stress contributes to the pathogenesis of hypoxic-ischemic encephalopathies. Platelet-activating factor (PAF) is generated during oxidant stress. We studied the vasomotor mode of actions of PAF on periventricular (PV) microvessels of fetal ( approximately 75% of term), newborn (1-3 days), and adult pigs. PAF constricted PV microvessels from fetal (29.27 +/- 2.6%) and newborn (22.14 +/- 3.2%) pigs but was ineffective in adults (<2.5%). Specific [(3)H]PAF binding was greater in fetus and newborn than in adults; a concordant developmental PAF-induced inositol phosphate formation was observed. PAF-induced vasoconstriction was abrogated by thromboxane A(2) (TXA(2)) synthase and receptor inhibitors, calcium channel blockers, and by removal of endothelium; vasoconstriction to TXA(2) mimetic U-46619 did not differ with age. Immunoreactive TXA(2) synthase expression and PAF-evoked TXA(2) formation revealed a fetus> newborn>adult profile. Thus the greater PAF-induced PV microvascular constriction in younger subjects seems attributable to greater PAF receptor density and mostly secondary to TXA(2) formation from endothelium. The resulting decrease in blood flow may contribute to the increased vulnerability of the PV brain regions to oxidant stress-induced injury in immature subjects.     

Initial frequency of alleles conferring resistance to Bacillus thuringiensis poplar in a field population of Chrysomela tremulae

Globally, the estimated total area planted with transgenic plants producing Bacillus thuringiensis (Bt) toxins was 12 million hectares in 2001. The risk of target pests becoming resistant to these toxins has led to the implementation of resistance-management strategies. The efficiency and sustainability of these strategies, including the high-dose plus refuge strategy currently recommended for North American maize, depend on the initial frequency of resistance alleles. In this study, we estimated the initial frequencies of alleles conferring resistance to transgenic Bt poplars producing Cry3A in a natural population of the poplar pest Chrysomela tremulae (Coleoptera: Chrysomelidae). We used the F(2) screen method developed for detecting resistance alleles in natural pest populations. At least three parents of the 270 lines tested were heterozygous for a major Bt resistance allele. We estimated mean resistance-allele frequency for the period 1999-2001 at 0.0037 (95% confidence interval = 0.00045-0.0080) with a detection probability of 90%. These results demonstrate that (i) the F(2) screen method can be used to detect major alleles conferring resistance to Bt-producing plants in insects and (ii) the initial frequency of alleles conferring resistance to Bt toxin can be close to the highest theoretical values that are expected prior to the use of Bt plants if considering fitness costs and typical mutation rates.     

What is the nature of the replicative niche of a stealthy bug named Brucella?

Brucella spp. are facultatively intracellular bacteria that persist and multiply in the macrophages of their mammalian hosts. The so-called phagosome to which they have adapted is their natural living niche. Characterization of this niche would facilitate an understanding of the true relationship between the host cell and the intracellular bacteria. This Opinion analyses and discusses the characteristic properties and genesis of this vacuole during phagocytosis as deduced from the virulence factors necessary for intracellular multiplication of the pathogen. We conclude that the replicative niche of Brucella spp.--the 'brucellosome'--differs from all other cellular organelles, and that it isolates the pathogen from certain cytoplasmic nutrients. Adaptation to the stress conditions encountered and the use of anaerobic respiration enable brucellae to replicate in the compartment they create.     

Structure of mammalian cytochrome P450 2C5 complexed with diclofenac at 2.1 A resolution: evidence for an induced fit model of substrate binding

The structure of the anti-inflammatory drug diclofenac bound in the active site of rabbit microsomal cytochrome P450 2C5/3LVdH was determined by X-ray crystallography to 2.1 A resolution. P450 2C5/3LVdH and the related enzyme 2C5dH catalyze the 4'-hydroxylation of diclofenac with apparent K(m) values of 80 and 57 microM and k(cat) values of 13 and 16 min(-1), respectively. Spectrally determined binding constants are similar to the K(m) values. The structure indicates that the pi-electron system of the dichlorophenyl moiety faces the heme Fe with the 3'- and 4'-carbons located 4.4 and 4.7 A, respectively, from the Fe. The carboxyl moiety of the substrate is hydrogen bonded to a cluster of waters that are also hydrogen bonded to the side chains of N204, K241, S289, and D290 as well as the backbone of the protein. The proximity of the diclofenac carboxylate to the side chain of D290 together with an increased binding affinity at lower pH suggests that diclofenac is protonated when bound to the enzyme. The structure exhibits conformational changes indicative of an adaptive fit to the substrate reflecting both the hydration and size of the substrate. These results indicate how structurally diverse substrates are recognized by drug-metabolizing P450 enzymes.