Glyoxylate metabolism and fatty acid oxidation in mango fruit during development and ripening

Throughout the development (maturation) of mango fruit the contents of citric and glyoxylic acids increased steadily. As the fruit matured the levels of isocitrate lyase, malate lyase and alanine: glyoxylate aminotransferase increased and reached maximum values prior to the time of harvesting. At and after harvest the levels of malate lyase and alanine : glyoxylate aminotransferase began to decrease but that of isocitrate lyase remained high until after the harvest when it decreased. The level of glyoxylate reductase was highest in the early developmental stage but declined as the fruit matured and ripened. As the fruit ripened, after harvest, the amounts of citric and glyoxylic acids decreased concomitant with a considerable increase in the levels of isocitrate dehydrogenase, malic dehydrogenase, malic enzyme and glyoxylate dehydrogenase.Fatty acid oxidizing capacity of mitochondria isolated from immature (developing) and postclimacteric fruit pulps was much less than that observed with mitochondria from preclimacteric and climacteric fruit. Glyoxylate stimulated the oxidation of caprylic, lauric, myristic and palmitic acids and inhibited the activity of isocitrate dehydrogenase in vitro.     

Mitochondrial enzymes in mango fruit during ripening

Mitochondria isolated from immature (developing), mature (unripe), and ripe mango pulp actively oxidized the intermediates of the Krebs cycle. The oxidation of citrate, oxoglutarate, succinate and malate by both unripe and ripe fruit mitochondria was several fold greater than that by mitochondria from immature fruit. The levels of malic dehydrogenase and succinic dehydrogenase increased with the onset of ripening, whereas the level of citrate synthase increased several fold on maturation but decreased six-fold on ripening. Isocitrate dehydrogenase and malic enzyme were very high in the immature fruit but after a sudden decrease in the matured fruit showed a considerable rise thereafter. The ratio of the activities of isocitrate lyase to isocitrate dehydrogenase is considerably higher in the immature fruit and greatest in the unripe (mature) fruit. This, together with a higher concentration of glyoxylate at these stages, indicate the operation of the glyoxylate bypass. Oxidized and reduced forms of pyridine nucleotides were estimated.     

Palmitic acid induces IP-10 expression in human macrophages via NF-kappaB activation

It is now recognized that cross-talk between adipocytes and adipose tissue stromal cells such as macrophages contributes to local and systemic inflammation. One factor from adipocytes that may participate in this interaction and that is frequently elevated in inflammatory conditions such as obesity, insulin resistance, and type 2 diabetes is free fatty acids (FFA). To investigate the potential for FFA to enhance macrophage inflammation, we exposed U937 macrophages to physiological levels (150 microM) of FFA. Palmitic acid (PA), the predominant saturated FFA released from adipose tissue, but not unsaturated FFA, induced an approximately 6-fold (p<0.05) increase in IP-10 gene expression (and 2- to 4-fold increases in IL-8, MCP-1, COX-2, and MIG). PA also induced an approximately 2-fold increase (p<0.05) in active NF-kappaB, and two structurally distinct NF-kappaB inhibitors effectively blocked PA-induced IP-10 gene expression. Conditioned medium from PA-treated cells increased lymphocyte migration 41% (p<0.05) which was significantly reduced by IP-10-neutralizing antibody. These results suggest that elevated concentrations of PA commonly present in obese and insulin resistant individuals can increase NF-kappaB-mediated expression of IP-10 in macrophages. These events in turn may lead to an increasing feed-forward loop of chronic inflammation.     

Effects of ethylene and acetylene on mango fruit ripening

Mangoes (var. Tommy Atkins) were exposed to ethylene and acetylene over a range of concentrations at high humidity for 24 h at 25°C, then ripened in air alone. Ripeness was assessed after 4 and 8 days by analysis of texture, colour development, soluble solids and acid contents. Ethylene in air at concentrations of 0.01 ml litre^-1 and above or acetylene at 1.0 ml litre^-1 were found to initiate ripening. Treatment with 0.01 ml litre^-1 acetylene resulted in limited softening but had no effect on the other ripening changes analysed. Individual ripening processes responded differently to treatment: texture changes were most rapidly affected, while the rate of acidity losses was often reduced in ethylene treated fruits. Acetylene-treated fruits at concentrations of 0.01 and 0.1 ml litre^-1 showed delayed ripening when compared to those treated with either 1.0 ml litre^-1 acetylene or ethylene. Increased acetylene concentrations of 2.0 ml litre^-1 gave a similar response to 1.0 ml litre^-1, although in some instances there were indications of inhibitory effects.     

Effect of pre-storage treatments on mango fruit ripening

The effectiveness of pre-storage treatments of nitrogen (low oxygen), heat and ethanol and acetaldehyde vapours were examined for their potential for improving mango storage. Mature green mango fruit (Mangifera indica L. cv. Keitt) were treated with low oxygen (< 3% oxygen, 97% nitrogen) for 72 h, acetaldehyde (0.12%) and ethanol (1%) vapours for 24 h or heat (38 ± 2°C) for 48 h prior to storage at 14°C. The nitrogen and ethanol treatments induced substantial levels of acetaldehyde and ethanol in the fruit. Initially the firmness of the nitrogen treated fruit remained higher than the control although later in storage this effect was lost. Differences in ripening were reflected in the total soluble solids and acidity levels, nitrogen maintaining a higher acidity and lower total soluble solids (less mature) whereas the heat treated fruit had lower acidity and higher total soluble solids (more mature). Ethanol and acetaldehyde treatments showed no effect. The use of a pre-storage treatment of nitrogen therefore had a beneficial effect on retarding ripening, although as storage progressed this effect was lost.     

Upsurge of particulate peroxidase in ripening banana fruit

Peroxidase was isolated from the pulp of ripening banana fruit and assayed with o-dianisidine as hydrogen-donor. Cell macerates contained soluble and particle-bound peroxidase. Soluble peroxidase levels did not appreciably differ in pre-climacteric, climacteric and post-climacteric fruit. Particulate peroxidase levels increased 3-fold with the initiation of the respiration climacteric and gradually declined with the onset of senescence. Bound peroxidase was released from cell wall and membrane fractions with washing in 0–8 M CaCl₂.     

Modulation of mango ripening by chemicals: physiological and biochemical aspects

During ripening, fleshy fruits undergo textural changes that lead to loss of tissue firmness and consequent softening due to cell wall dismantling carried out by different and specifically expressed enzymes. The effect of various chemical treatments on the ripening of mango fruit (Mangifera indica) was investigated at physiological and biochemical level. Based on changes in respiration, firmness, pH, total soluble sugar and a cell wall degrading enzyme pectate lyase (PEL) activity, treatment with 1-methylcyclopropene (1-MCP), silver nitrate (AgNO₃), gibberlic acid (GA₃), sodium metabisulphite (SMS) and ascorbic acid led to delaying of ripening process while those of ethrel and calcium chloride (CaCl₂) enhanced the process. PEL of mango was found to be inhibited by certain metabolites present in dialysed ammonium sulphate enzyme extract as well as EDTA. Mango PEL activity exhibited an absolute requirement for Ca²⁺ and an optimum pH of 8.5.     

Compositional changes in cell wall polymers during mango fruit ripening

Softening of mango fruit has been investigated by analysis of ripening related changes in the composition of the fruit cell walls. There is an apparent overall loss of galactosyl and deoxyhexosyl residues during ripening, the latter indicating degradation of the pectin component of the wall. The loss of galactose appears to be restricted to the chelator soluble fraction of the wall pectin, whilst loss of deoxyhexose seems to be more evenly distributed amongst the pectin. The chelator soluble pectin fraction is progressively depolymerised and becomes more polydisperse during ripening. These changes are similar to those occurring in other fruit and are related to the action of wall hydrolases during ripening.     

The expression of alternative oxidase and uncoupling protein during fruit ripening in mango

The expression of alternative oxidase (Aox) and uncoupling proteins (Ucp) was investigated during ripening in mango (Mangifera indica) and compared with the expression of peroxisomal thiolase, a previously described ripening marker in mango. The multigene family for the Aox in mango was expressed differentially during ripening. Abundance of Aox message and protein both peaked at the ripe stage. Expression of the single gene for the Ucp peaked at the turning stage and the protein abundance peaked at the ripe stage. Proteins of the cytochrome chain peaked at the mature stage of ripening. The pattern of protein accumulation suggested that increases in cytochrome chain components played an important role in facilitating the climacteric burst of respiration and that the Aox and Ucp may play a role in post-climacteric senescent processes. Because both message and protein for the Aox and Ucp increased in a similar pattern, it suggests that their expression is not controlled in a reciprocal manner but may be active simultaneously.     

Palmitic acid uptake by the rat soleus muscle in vitro.

Abstract: The rate of fatty acid uptake, oxidation, and deposition in skeletal muscles in relation to total and unbound to albumin fatty acids concentration in the medium were investigated in the incubated rat soleus muscle. An immunohistochemical technique was applied to demonstrate whether the albumin-bound fatty acid complex from the medium penetrates well within all areas of the muscle strips. It was found that the percentage of incorporation of palmitic acid into intramuscular lipids was fairly constant, independently of the fatty acid concentration in the medium, and amounted to 63-72% for triacylglycerols, 7-12% for diacylglycerols-monoacylglycerols, and 19-26% for phospholipids. Both palmitic acid incorporation into the muscle triacylglycerol stores and its oxidation to CO2 closely correlated with an increase in both total and unbound to albumin fatty acid concentrations in the incubation medium. Under conditions of increased total but constant unbound to albumin palmitic acid concentrations, the incorporation of palmitic acid into triacylglycerols and its oxidation to CO2 were also increased, but to a lower extent. This supports the hypothesis that the cellular fatty acid metabolism depends not only on the availability of fatty acids unbound to albumin, but also on the availability of fatty acids complexed to albumin.     

beta-Galactosidase and its significance in ripening of "Saijyo" Japanese Persimmon fruit

The fruit extracts of ripening cv. Japanese Persimmon, "Saijyo", contained a number of glycosidases and glycanases. Among them, beta-galactosidase appeared to be the most significant, and the activity increased in parallel with tissue ripening. Persimmon beta-galactosidase was presented in at least three isoforms, beta-galactosidase-I (pI = 4.88), beta-galactosidase-II (pI = 6.76), and beta-galactosidase-III (pI = 7.05). beta-Galactosidase-III had exo-type galactanase activity, while the others did not. The activity of endo-type glycanases was a maximum in immature green or yellow fruits. The firmness of the pulp tissue decreased dramatically, and the amount of water-soluble polysaccharide (WSS) increased. The enzyme activities of exo-type glycosidases, especially beta-galactosidase, appeared maximal in mature red fruits. The amount of extractable pectin remained unchanged, although the galactose content of the high-molecular-weight fraction in WSS decreased dramatically. These results suggest that the ripening of persimmon was caused by the solubilization of pectic polysaccharide by endo-type glycanases and digestion by exo-type glycosidases. beta-Galactosidase, in particular, seemed to play a major role in ripening the fruit.     

The purification and properties of peroxidase in Mycobacterium tuberculosis H37Rv and its possible role in the mechanism of action of isonicotinic acid hydrazide.

Peroxidase from Mycobacterium tuberculosis H37Rv was purified to homogeneity. The homogeneous protein exhibits catalase and Y (Youatt's)-enzyme activities in addition to peroxidase activity. Further confirmation that the three activities are due to a single enzyme was accomplished by other criteria, such as differential thermal inactivation, sensitivity to different inhibitors, and co-purification. The Y enzyme (peroxidase) was separated from NADase (NAD+ glycohydrolase) inhibitor by gel filtration on Sephadex G-200. The molecular weights of peroxidase and NADase inhibitor, as determined by gel filtration, are 240000 and 98000 respectively. The Y enzyme shows two Km values for both isoniazid (isonicotinic acid hydrazide) and NAD at low and high concentrations. Analysis of the data by Hill plots revealed that the enzyme has one binding site at lower substrate concentrations and more than one at higher substrate concentration. The enzyme contains 6g-atoms of iron/mol. Highly purified preparations of peroxidases from different sources catalyse the Y-enzyme reaction, suggesting that the nature of the reaction may be a peroxidatic oxidation of isoniazid. Moreover, the Y-enzyme reaction is enhanced by O2. Isoniazid-resistant mutants do not exhibit Y-enzyme, peroxidase or catalase activities, and do not take up isoniazid. The Y-enzyme reaction is therefore implicated in the uptake of the drug.     

Cellulase in latex and its possible significance in cell differentiation

Summary Cellulase was found to be present in the latex of species with articulated laticifers but it could not be detected in the latex of species with nonarticulated laticifers. It is suggested that cellulase is involved in the removal of end walls during the differentiation of articulated laticifers.     

Hormonal activation of mammary gland peroxidase.

Ultrastructural cytochemistry was used to detect an endogenous peroxidase in the rat mammary gland. The enzyme was identified only during the latter half of pregnancy and during lactation, indicating its possible dependence upon hormones. To test this hypothesis, specific hormones associated with the development and differentiation of the mammary gland were used both in vivo and in vitro in an effort to induce, or unmask, the activity of the enzyme. Estrogen injected into nonpregnant rats induced some peroxidase activity in the mammary glands of a few animals. Two hormone combinations tested in organ cultures of mouse mammary gland were able to activate the enzyme: (1) dexamethasone + insulin and (2) dexamethasone + insulin + prolactin.     

Ethylene production and peroxidase activity during tomato fruit ripening

Peroxidase activity and enzymic production of ethylene werestudied in tomato fruits (Lycopersicon esculentum MILL.) at3 ripeness stages. As the fruit ripens, one isoperoxidase disappears,and 3 new ones are formed. Activity of peroxidase and of ethylene-formingenzyme both increased 3 to 4 times as the fruit ripened. Histochemicalstaining showed that peroxidase is confined to the outermostand innermost layers of the pericarp, the placental tissue andvascular tissues; stained particles were neither mitochondrianor plastids. (Received October 27, 1969; )     

Effects of 1-MCP and exogenous ethylene on fruit ripening and antioxidants in stored mango

Mango (Mangifera indica L. cv. Tainong) fruits were harvested at the green-mature stage in Hainan and air-freighted to the laboratory at Peking. The fruits were treated with either 1 μl l⁻¹ 1-MCP or 5 μl l⁻¹ ethylene for 24 h and stored at 20°C for up to 16 days. 1-MCP maintained fruit firmness, whereas exogenous ethylene decreased fruit firmness. Exogenous ethylene accelerated the increase in ethylene and 1-aminocyclopropane-1-carboxylate (ACC) oxidase, whereas 1-MCP reduced both. Exogenous ethylene stimulated and 1-MCP inhibited the production of H₂O₂ of mango fruit during storage. Ascorbic acid was maintained at a high concentration in 1-MCP-treated fruit but was low in ethylene-treated fruit. 1-MCP inhibited activities of antioxidant enzymes including catalase, superoxide dismutase and ascorbate peroxidase. These results suggest that 1-MCP could play a positive role in regulating the activated oxygen metabolism balance. Baogang Wang and Jianhui Wang contributed equally to this work.     

Changes in peel pigmentation during ripening of mango fruit (Mangifera indica var. Tommy Atkins)

The pigments in the peel of Tommy Atkins mango were analysed at six stages during ripening at 22 ^oC. The loss of green colour and the development of yellow colouration was associated with an almost complete loss of chlorophyll and an increase in carotenoids. Anthocyanin content showed a slight decrease during ripening. An ultrastructural study showed plastids in green fruit with a well developed grana network system. On ripening the chloroplasts underwent extensive disorganisation which was associated with the development of large osmiophilic globules.