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Biomedical subjects

P Matile

Publications and source records attributed to P Matile.

At least 19 recordsLinked to original sources
PubMed2000

Biochemistry of Indian summer: physiology of autumnal leaf coloration.

The autumnal coloration of foliage in deciduous trees represents a most spectacular phytogerontological phenomenon. It is primarily due to the progressive loss of chlorophyll coinciding with the partial retention of carotenoids. Leaf senescence is a developmental process that is aimed at the recycling of nutrients to perennial parts of the tree for reuse upon the production of new foliage in spring. The remobilization of protein in senescing chloroplasts requires the dismantling of pigment-protein complexes and concomitant photodynamic inactivation of chlorophyll. Detoxification of chlorophyll is achieved by enzymic opening of the porphyrin macrocycle followed by modifications of the resulting linear tetrapyrrole and storage of colorless final catabolites in the vacuoles of degreening leaf cells. The polychromatic beauty of autumnal trees is due to species-specific variations of the degree of carotenoid retention, new synthesis of red anthocyanins and, upon cell death, the formation of dark oxidation products of phenolics.

Biochemistry↗
PubMed2000

Chlorophyll breakdown in Chlorella protothecoides: characterization of degreening and cloning of degreening-related genes.

Chlorella protothecoides cultures grown in a nitrogen-free bleaching medium (BM-N) in the dark rapidly degraded chlorophyll (Chl) to red catabolites. This degreening process was investigated under different growth conditions. Supply of nitrogen to the culture medium (BM+N) inhibited bleaching and the synthesis of catabolites as did the addition to BM-N of cycloheximide or a chelator, 2,2'-bipyridyl. In contrast, chloramphenicol or the protease inhibitor E64 had no effect. During bleaching, Chl breakdown was accompanied by the degradation of cellular proteins such as light-harvesting complex II, cytochrome f and protochlorophyllide oxido-reductase. During growth in BM-N, protease activity increased and proteins immunologically detectable with an antibody against a senescence-enhanced cysteine protease accumulated. cDNAs from BM-N and BM+N cells were used for differential and subtractive screening to isolate cDNAs representing genes with degreening-enhanced expression (dee) in C. protothecoides. Several different dees were identified with different patterns of expression during Chlorella growth but which were all expressed at higher levels during bleaching. Among these, dee4 was most abundant and its expression was exclusive in BM-N cultures. Analysis of the dee sequences showed that they encode different proteins including a novel amino acid carrier (dee4), ferritin, ATP-dependent citrate lyase, a Ca2+-binding protein, MO25, ubiquinone-cytochrome c-reductase and several new proteins.

Algal Proteins↗
PubMed1998

The key step in chlorophyll breakdown in higher plants. Cleavage of pheophorbide a macrocycle by a monooxygenase.

Chlorophyll breakdown in green plants is a long-standing biological enigma. Recent work has shown that pheophorbide a (Pheide a) derived from chlorophyll (Chl) is converted oxygenolytically into a primary fluorescent catabolite (pFCC-1) via a red Chl catabolite (RCC) intermediate. RCC, the product of the ring cleavage reaction catalyzed by Pheide a oxygenase, which is suggested to be the key enzyme in Chl breakdown in green plants, is converted into pFCC-1 by a reductase. In the present study, an in vitro assay comprising 18O2 Pheide a oxygenase and RCC reductase yielded labeled pFCC-1. Fast atom bombardment-mass spectrometric analysis of the purified pFCC-1 product revealed that only one of the two oxygen atoms newly introduced into Pheide a in the course of the cleavage reaction is derived from molecular oxygen. Analysis of the fragment ions located the oxygen atom derived from molecular oxygen on the formyl group of pyrrole B. This finding demonstrates that the cleavage of Pheide a in vascular plants is catalyzed by a monooxygenase. Chlorophyll breakdown is therefore indicated to be mechanistically related in higher plants and in the green alga Chlorella protothecoides.

Chlorella↗
PubMed1998

An ABC-transporter of Arabidopsis thaliana has both glutathione-conjugate and chlorophyll catabolite transport activity.

An ABC-transporter of Arabidopsis thaliana exhibiting high sequence similarity to the human (MRP1) and yeast (YCF1) glutathione-conjugate transporters has been analysed and used to complement a cadmium-sensitive yeast mutant (DTY168) that also lacks glutathione-conjugate transport activity. Comparison of the hydrophobicity plots of this A. thaliana MRP-like protein with MRP1 and YCF1 demonstrates that the transmembrane domains are conserved, even at the N-terminus where sequence identity is low. Cadmium resistance is partially restored in the complemented ycf1 mutant, and glutathione-conjugate transport activity can be observed as well. The kinetic properties of the A. thaliana MRP-like protein (AtMRP3) are very similar to those previously described for the vacuolar glutathione-conjugate transporter of barley and mung bean. Furthermore, a hitherto undescribed ATP-dependent transport activity could be correlated with the gene product, i.e. vesicles isolated from the complemented yeast, but not from DTY168 or the wild type, take up the chlorophyll catabolite Bn-NCC-1. The results indicate that the product of the MRP-like gene of A. thaliana is capable of mediating the transport of the two different classes of compounds.

ATP-Binding Cassette Transporters↗
PubMed1996

How plants dispose of chlorophyll catabolites. Directly energized uptake of tetrapyrrolic breakdown products into isolated vacuoles.

During the yellowing of leaves the porphyrin moiety of chlorophyll is cleaved into colorless linear tetrapyrrolic catabolites, which eventually are deposited in the central vacuoles of mesophyll cells. In senescent cotyledons of rape, Brassica napus, three nonfluorescent chlorophyll catabolites (NCCs), accounting for practically all the chlorophyll broken down, were found to be located in the vacuoles (vacuoplasts) prepared from protoplasts. Transport of catabolites across the tonoplast was studied with vacuoles isolated from barley mesophyll protoplasts in conjunction with a radiolabeled NCC, Bn-NCC-1, prepared from senescent rape cotyledons. The uptake of Bn-NCC-1 into vacuoles was against a concentration gradient and strictly dependent on MgATP and it followed saturation kinetics with a Km of approximately 100 microM. Although the hydrolysis of ATP was required, transport was apparently independent of the vacuolar proton pumps: accumulation of the NCC occurred both in the presence of the H+-ATPase inhibitor bafilomycin and after destroying the DeltapH between the vacuolar sap and the medium. ATP could be replaced by GTP or UTP, and the transport was inhibited in the presence of vanadate. Chlorophyll catabolites isolated from senescent barley leaves competed with the rape-specific substrate for uptake into the vacuoles. Compounds such as the glutathione conjugate of N-ethylmaleimide and taurocholate, which are known to be transported across the tonoplast in a primary active mode, did not significantly inhibit uptake of Bn-NCC-1. Although the heme catabolites biliverdin and bilirubin inhibited the uptake of the NCC, this effect is caused by unspecific binding to the vacuolar membrane rather than to the specific inhibition of carrier-mediated transport. Taken together, the results demonstrate that barley mesophyll vacuoles are constitutively equipped with a directly energized carrier that transports tetrapyrrolic catabolites of chlorophyll into the vacuole.

Biological Transport↗
PubMed1988

Catabolites of chlorophyll in senescing barley leaves are localized in the vacuoles of mesophyll cells.

Senescing barley leaves accumulate a series of pink pigments with the chemical properties of catabolites derived from chlorophyll. Levels of the major component of this group of pigments were quantified by HPLC and shown to be maximal in tissues exhibiting maximal rates of chlorophyll degradation. Protoplasts were isolated from senescent leaf tissue and fractionated to yield intact vacuoles and plastids. Although small but significant proportions both of total catabolites and of the dominant component of the series were recovered from the plastid fraction, the vast bulk of these compounds could be assigned to the vacuole. These observations suggest a role for the vacuole in the later stages of chlorophyll breakdown during senescence.

Journal Article↗
PubMed1988

Transport and subcellular localization of polyamines in carrot protoplasts and vacuoles.

Putrescine and spermidine uptake in carrot (Daucus carota L., cv "Tip top") protoplasts and isolated vacuoles was studied. Protoplasts and vacuoles accumulated polyamines very quickly, with maximum absorption within 1 to 2 minutes. The insertion of a washing layer containing 100 millimolar unlabeled putrescine or spermidine did not change this pattern, but strongly reduced the uptake of putrescine and spermidine in protoplasts and in vacuoles. The dependence of spermidine uptake on the external concentration was linear up to the highest concentrations tested in protoplasts, while that in vacuoles showed saturation kinetics below 1 millimolar (K(m) = 61.8 micromolar) and a linear component from 1 to 50 millimolar. Spermidine uptake in protoplasts increased linearly between pH 5.5 and 7.0, while there was a distinct optimum at pH 7.0 for vacuoles. Preincubation of protoplasts with 1 millimolar Ca(2+) affected only surface binding but not transport into the cells. Nonpermeant polycations such as La(3+) and polylysine inhibited spermidine uptake into protoplasts. Compartmentation studies showed that putrescine and spermidine were partly vacuolar in location and that exogenously applied spermidine could be recovered inside the cells. The characteristics of the protoplast and vacuolar uptake system induce us to put forward the hypothesis of a passive influx of polyamines through the plasmalemma and of the presence of a carrier-mediated transport system localized in the tonoplast.

Journal Article↗
PubMed1986

Regulation of Fructan Metabolism in Leaves of Barley (Hordeum vulgare L. cv Gerbel).

Excised primary leaf blades of barley (Hordeum vulgare L. cv Gerbel) rapidly synthesized large quantities of fructan in the light and, upon transfer to the dark, they rapidly degraded it again. In the course of such a light/dark cycle the activities of sucrose-sucrose-fructosyltransferase (SST), fructan hydrolase, and invertase were measured in cell-free extracts of the blades. SST activity increased 20-fold within 24 hours in the light and disappeared again upon transfer to the dark during a similar period of time. Cycloheximide inhibited the increase of SST activity in the light indicating de novo synthesis. The loss of SST activity in the dark, however, was unaffected by cycloheximide. No SST activity appeared in the light if photosynthesis was inhibited by lowering the CO(2) concentration in the atmosphere. However, SST activity and fructan synthesis were induced even in the dark and at a low CO(2) concentration when the leaf blades were immersed in a solution of sucrose. Several other sugars, maltose and fructose in particular, had the same effect. Trehalose induced SST activity but no fructan synthesis occurred. The activities of fructan hydrolase and invertase changed little during the light/dark cycle. It is suggested that the control of SST activity in conjunction with the supply of photosynthates plays a key role in the regulation of fructan metabolism.

Journal Article↗
PubMed1982

A malic Acid permease in isolated vacuoles of a crassulacean Acid metabolism plant.

Vacuoles isolated from mesophyll protoplasts of the Crassulacean acid metabolism plant Bryophyllum daigremontianum take up [(14)C]l-malic acid from the medium. The initial rates of uptake show saturation kinetics (apparent K(m) about 1 millimolar). In competition experiments, the uptake rates of l-malic acid are greatly reduced in the presence of a surplus of d-malic and tartronic acid. A number of other acids are much less effective and aspartic and isocitric acid have virtually no effect. The uptake rate of malic acid is unchanged in the presence of ATP and the uncouplers dinitrophenol and carbonyl cyanide m-chlorophenyl hydrazone. When the vacuoles are isolated in the absence of bovine serum albumin or when 1 millimolar HgCl(2) is added, they are inactive in transport but retain their malic acid pool. The existence of a specific permease which catalyzes an exchange diffusion of malic acid across the vacuolar membrane is postulated.

Journal Article↗
PubMed1979

Some properties of vacuoles isolated from Neurospora crassa slime variant.

A method for the isolation of vacuoles based on polybase induced lysis of protoplasts of the cell wall deficient Neurospora crassa slime variant is described. Isolated vacuoles are characterized by 12 to 50 times increased specific activities of several hydrolases as compared with the total homogenate of protoplasts. Total alpha-amino nitrogen, arginine, and polyphosphate are also greatly enriched in these vacuoles. Vacuoles are equipped with a permease for the transport of basic amino acids across the tonoplast.

Amino Acids↗
PubMed1975

Ribonuclease in senescing morning glory: purification and demonstration of de novo synthesis.

Isolated flower buds and flowers of Ipomoea tricolor went through the same stages of development as those attached to the plant. Ribonuclease activity increased sharply in both cases during the time of flower fading and aging. Affinity chromatography using guanosine diphosphate-Sepharose was employed for fast and efficient purification of ribonuclease. Flowers which were kept on D(2)O during the senescence phase incorporated deuterium into ribonuclease as shown by isopycnic density gradient centrifugation in CsCl, suggesting that ribonuclease was de novo synthesized during aging of the flower.

Journal Article↗
PubMed1971

Isolation of glucanase-containing particles from budding Saccharomyces cerevisiae.

In an investigation of the role of glucanases in modifying yeast cell walls at the location of new buds, vesicles derived from the endoplasmic reticulum, which are secreted locally into the cell wall of growing buds and may be involved in the secretion of glucanases, have been isolated.In yeast, exo-beta-1,3-glucanase (EC 3.2.1.6) is present both extra- and intracellularly. Exponentially growing cells contain about 16% of the enzyme activity intracellularly (within the plasmalemma). Most, if not all, of this intracellular glucanase is sedimentable. Of the three classes of subcellular particles that contain glucanase, one is almost completely absent from stationary phase cells and almost absent from cells of the late budding phase of the budding cycle. These particles were isolated from budding cells by combined differential and density gradient centrifugation. They contain exo- and endo-beta-1,3-glucanases, mannan, and protein. The isolate consists mainly of membrane-bounded particles with diameters corresponding to those of the secretory vesicles observed in situ. It is concluded that these particles are identical with the vesicles derived from the endoplasmic reticulum.

Cell Wall↗