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1.
The interconversion of chlorophyll a and chlorophyll b, referred to as the chlorophyll cycle, plays a crucial role in the processes of greening, acclimation to light intensity, and senescence. The chlorophyll cycle consists of three reactions: the conversions of chlorophyll a to chlorophyll b by chlorophyllide a oxygenase, chlorophyll b to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, and 7-hydroxymethyl chlorophyll a to chlorophyll a by 7-hydroxymethyl chlorophyll a reductase. We identified 7-hydroxymethyl chlorophyll a reductase, which is the last remaining unidentified enzyme of the chlorophyll cycle, from Arabidopsis thaliana by genetic and biochemical methods. Recombinant 7-hydroxymethyl chlorophyll a reductase converted 7-hydroxymethyl chlorophyll a to chlorophyll a using ferredoxin. Both sequence and biochemical analyses showed that 7-hydroxymethyl chlorophyll a reductase contains flavin adenine dinucleotide and an iron-sulfur center. In addition, a phylogenetic analysis elucidated the evolution of 7-hydroxymethyl chlorophyll a reductase from divinyl chlorophyllide vinyl reductase. A mutant lacking 7-hydroxymethyl chlorophyll a reductase was found to accumulate 7-hydroxymethyl chlorophyll a and pheophorbide a. Furthermore, this accumulation of pheophorbide a in the mutant was rescued by the inactivation of the chlorophyll b reductase gene. The downregulation of pheophorbide a oxygenase activity is discussed in relation to 7-hydroxymethyl chlorophyll a accumulation. 相似文献
2.
Brackenbury J 《Journal of insect physiology》2000,46(12):1517-1527
The locomotory kinematics of Chironomus plumosus larvae and pupae were investigated in order to determine how different locomotory techniques may be related to (a) possible underlying patterns of muscle activation and (b) the particular lifestyles and behaviours of these juvenile stages. Larvae display three independent modes of motile activity: swimming, crawling and whole-body respiratory undulation. Swimming and respiratory undulation involve the use of metachronal waves of body bending which travel in a head-to-tail direction. Whereas swimming is produced by side-to-side flexures of the whole body, respiratory undulation employs a sinusoidal wave. Crawling appears to result from an independent programme of muscle activation. Instead of a longitudinally transmitting metachronal wave of body flexure, a simultaneous arching of the body, combined with the alternating use of the abdominal and prothoracic pseudopods as anchorage points, produces a form of locomotion analogous to caterpillar-looping. Larval swimming has a set speed and rhythm and is an 'all-or-nothing' locomotory manoeuvre, but the neural programme controlling larval crawling is adaptable; switching from a less to a more slippery substrate resulted in a shorter, faster stepping pattern. The pupa displays two swimming modes, somersaulting and eel-like whole-body undulation, the former being principally a brief, escape manoeuvre, the latter being a faster form of locomotion employed to deliver the pupa to the surface prior to adult emergence. Comparison with the pupa of the culicid Culex pipiens shows that this insect also uses the somersault mechanism but at a higher cycle frequency which produces a faster swimming speed. This appears to be related to differences in lifestyle; the surface-living culicid pupa is exposed to greater predator threat than the bottom-dwelling chironomid pupa, and consequently needs a faster escape. 相似文献
3.
Mice undergoing a mild GVHR exhibited an enhanced response to PVP considered to be independent of T-helper function and simultaneously, a decreased response to SRBC, known to be T-cell dependent. Such mice had a reduced number of T cells in their spleens expressed by a lower reactivity to T-lectins PHA and Con A and by a decrease in the number of cells killed by anti θ serum. These mice did not show, however, a substantial change in the activity of B lymphocytes contained in their spleens, since the PFC and the mitogenic response to LPS, as well as the number of immunoglobulin bearing cells were similar to that of controls. These results suggest that the enhanced response to PVP in mice undergoing a mild GVHR is a result of the elimination of a certain T-cell population which seems to regulate the immune response to this antigen. 相似文献
4.
Filippo Menolascina Gianfranco Fiore Emanuele Orabona Luca De Stefano Mike Ferry Jeff Hasty Mario di Bernardo Diego di Bernardo 《PLoS computational biology》2014,10(5)
We describe an innovative experimental and computational approach to control the expression of a protein in a population of yeast cells. We designed a simple control algorithm to automatically regulate the administration of inducer molecules to the cells by comparing the actual protein expression level in the cell population with the desired expression level. We then built an automated platform based on a microfluidic device, a time-lapse microscopy apparatus, and a set of motorized syringes, all controlled by a computer. We tested the platform to force yeast cells to express a desired fixed, or time-varying, amount of a reporter protein over thousands of minutes. The computer automatically switched the type of sugar administered to the cells, its concentration and its duration, according to the control algorithm. Our approach can be used to control expression of any protein, fused to a fluorescent reporter, provided that an external molecule known to (indirectly) affect its promoter activity is available. 相似文献
5.
The question of virginity testing in Turkey 总被引:2,自引:0,他引:2
Pelin SS 《Bioethics》1999,13(3-4):256-261
Pre-marital sex for a woman is regarded as wrong in my country. As a result, it is socially forbidden for a woman to engage in this act. In order to present a woman as a virgin on her marriage day, she is subjected to pressure, and put under control both by her family and societal norms. However, a man is free and never made to suffer any of the above. A woman found to be a virgin on her first night of marriage is seen as a normal person while one suspected to have lost her virginity is made to undergo a series of medical examinations to bring clarity to her situation. 相似文献
6.
Rock-scissors-paper and the survival of the weakest. 总被引:4,自引:0,他引:4
In the children's game of rock-scissors-paper, players each choose one of three strategies. A rock beats a pair of scissors, scissors beat a sheet of paper and paper beats a rock, so the strategies form a competitive cycle. Although cycles in competitive ability appear to be reasonably rare among terrestrial plants, they are common among marine sessile organisms and have been reported in other contexts. Here we consider a system with three species in a competitive loop and show that this simple ecology exhibits two counter-intuitive phenomena. First, the species that is least competitive is expected to have the largest population and, where there are oscillations in a finite population, to be the least likely to die out. As a consequence an apparent weakening of a species leads to an increase in its population. Second, evolution favours the most competitive individuals within a species, which leads to a decline in its population. This is analogous to the tragedy of the commons, but here, rather than leading to a collapse, the 'tragedy' acts to maintain diversity. 相似文献
7.
The response of parameters of plasma cholesterol metabolism was studied in baboons adapted either to a low-fat, low-cholesterol diet or a high-fat, high-cholesterol diet. Animals adapted to the low-fat diet responded to a single low-fat or high-fat meal, as do normal humans, by a stimulation of cholesterol transport from blood cells to plasma, a stimulation of esterification of cholesterol, and a stimulation of cholesteryl ester transfer to very low and low density lipoproteins. While fasting rates of esterification and transfer increased as a result of diet-induced hypercholesterolemia, the postprandial response was reversed, so that postprandial metabolism was characterized by a movement of cholesterol from plasma to blood cells, an inhibition of cholesterol esterification, and a net transfer of cholesteryl esters from VLDL and LDL to HDL. These data indicate that the effects of postprandial lipemia on plasma cholesterol metabolism critically depend upon fasting plasma cholesterol levels. 相似文献
8.
N. Munier 《Ecological Indicators》2011,11(5):1020-1026
This paper proposes a methodology for establishing a set of sustainability indicators as a baseline to measure the state of a city, and after appropriate actions are taken, to assess performance, to determine if changes point to improvements regarding goals. The methodology starts with choosing a procedure for identification, scope, evaluation, and level of indicators to build the initial dataset. As a second step, produces a reduced set of indicators, complying with all criteria imposed, and selected under the condition of extracting the maximum amount of information from the initial dataset. 相似文献
9.
Myotoxin a, a small basic polypeptide isolated from the venom of prairie rattlesnake (Crotalus viridis viridis), has been shown to bind to sarcoplasmic reticulum (SR) Ca(2+)-ATPase. The attachment of myotoxin a to Ca(2+)-ATPase is believed to cause uncoupling of the calcium pump. In order to further elucidate which portion of myotoxin a is important for the uncoupling action, five peptides were synthesized and two peptide fragments were obtained by chemical cleavage. These peptides correspond to discrete portions of the primary sequence of myotoxin a. The peptides are equivalent to the primary sequence of myotoxin a from 1 to 16 residues, 7 to 22 residues, 13 to 28 residues, 19 to 34 residues, and 25 to 42 residues. Chemically produced fragments are equivalent to 1 to 28 residues and 29 to 42 residues of myotoxin a. Peptides of the sequences "YKQCHKKGGHCFPKEK" and "LGKMDCRWKWKCCKKGSG" of myotoxin a inhibited 45Ca uptake into isolated SR and bound to Ca(2+)-ATPase. The same peptides caused weak skeletal muscle vacuolization similar to that caused by native myotoxin a and increased serum creatine kinase activity. The active peptides correspond to the N-terminal and C-terminal portions of myotoxin a. The inactive or less active peptides have sequences which correspond to the middle sequence of myotoxin a. From this study, both the N-terminal and the C-terminal regions of primary sequence of myotoxin a are required to express myotoxin a's biological activity. 相似文献
10.
D'Angelo A Geroldi D Hancock MA Valtulina V Cornaglia AI Spencer CA Emanuele E Calligaro A Koschinsky ML Speziale P Visai L 《Biochimica et biophysica acta》2005,1687(1-3):1-10
Lipoprotein(a) [Lp(a)] entrapment by vascular extracellular matrix may be important in atherogenesis. We sought to determine whether laminin, a major component of the basal membrane, may contribute to Lp(a) retention in the arterial wall. First, immunohistochemistry experiments were performed to examine the relative distribution of Lp(a) and laminin in human carotid artery specimens. There was a high degree of co-localization of Lp(a) and laminin in atherosclerotic specimens, but not in non-atherosclerotic sections. We then studied the binding interaction between Lp(a) and laminin in vitro. ELISA experiments showed that native Lp(a) particles and 17K and 12K recombinant apolipoprotein(a) [r-apo(a)] variants interacted strongly with laminin whereas LDL, apoB-100, and the truncated KIV(6-P), KIV(8-P), and KIV(9-P) r-apo(a) variants did not. Overall, the ELISA data demonstrated that Lp(a) binding to laminin is mediated by apo(a) and a combination of the lysine analogue epsilon-aminocaproic acid and salt effectively decreases apo(a) binding to laminin. Secondary binding analyses with 125I-labeled r-apo(a) revealed equilibrium dissociation constants (K(d)) of 180 and 360 nM for the 17K and 12K variants binding to laminin, respectively. Such similar K(d) values between these two r-apo(a) variants suggest that isoform size does not appear to influence apo(a) binding to laminin. In summary, our data suggest that laminin may bind to apo(a) in the atherosclerotic intima, thus contributing to the selective retention of Lp(a) in this milieu. 相似文献
11.
Pseudomonas aeruginosa DNA ligase D (PaeLigD) exemplifies a family of bacterial DNA end-joining proteins that consist of a ligase domain fused to a polymerase domain and a putative nuclease module. The LigD polymerase preferentially adds single ribonucleotides at blunt DNA ends and, as we show here, is also capable of adding up to 4 ribonucleotides to a DNA primer-template. We report that PaeLigD has an intrinsic ability to resect the short tract of 3'-ribonucleotides of a primer-template substrate to the point at which the primer strand has a single 3'-ribonucleotide remaining. The failure to digest beyond this point reflects a requirement for a 2'-OH group on the penultimate nucleoside of the primer strand. Replacing the 2'-OH by a 2'-F, 2'-NH2, 2'-OCH3, or 2'-H abolishes the resection reaction. The ribonucleotide resection activity resides within a 187-amino acid N-terminal nuclease domain and is the result of at least two component steps: (i) the 3'-terminal nucleoside is first removed to yield a primer strand with a ribonucleoside 3'-PO4 terminus, and (ii) the 3'-PO4 is hydrolyzed to a 3'-OH. The 3'-ribonuclease and 3'-phosphatase activities are both dependent on a divalent cation, specifically manganese. PaeLigD preferentially remodels the 3'-ends of a duplex primer-template substrate rather than a single strand of identical composition, and it prefers DNA primer strands containing a short 3'-ribonucleotide tract to an all-RNA primer. The nuclease domain of PaeLigD and its bacterial homologs has no apparent structural or mechanistic similarity to previously characterized nucleases. Thus, we surmise that it exemplifies a novel phosphoesterase family, defined in part by conserved residues Asp-50, Arg-52, and His-84, which are essential for the 3'-ribonuclease and 3'-phosphatase reactions. 相似文献
12.
Multicultural society and everyday cultural racism: second generation of Ethiopian Jews in Israel's ‘crisis of modernization’ 总被引:1,自引:0,他引:1
Uri Ben-Eliezer 《Ethnic and racial studies》2013,36(5):935-961
Abstract The core of this article sets out to examine the extent to which a multicultural society can prevent cultural racism, which, like multiculturalism, is by definition based on a culture of diversity and separation. The ‘first modernity’ was organized along national lines, with a centralist state that opted to create an essentialist and uncontested national identity. Immigrants, especially those who came from ‘third world’ countries, were expected to undergo a process of assimilation, and to integrate into the dominant culture by relinquishing their particular past and tradition. Multiculturalism, which emerged historically as a criticism of that perspective, aims at creating a kaleidoscope of associations and cultural communities, which inevitably presents a challenge to the one ‘truth’ of the nation-state with the argument that this ‘truth’ favours some groups over others. Within the multicultural model, identity politics of various groups is perceived as a means to achieve recognition, acceptance, respect and even public affirmation of differences. However, do multicultural society and identity-related differences provide a solution to cultural racism as well? Investigating the second generation of the Ethiopian Jews, who migrated to Israel during its transformation from ethno-national republicanism to a neo-liberal, multicultural society, can help answer this question. By presenting their patterns of association, character of protest activities and the newly formed hybrid identity that Ethiopian youth have developed as a means to liberate themselves from a discriminating reality, and by examining the Others’ reaction to that challenge, this article uncovers certain mechanisms and methods of action through which a multicultural society, having a thin and mild version of multiculturalism, does not diminish cultural racism, particularly its everyday non-institutional version, but in fact augments it. 相似文献
13.
Tucker RP Beckmann J Leachman NT Schöler J Chiquet-Ehrismann R 《Molecular biology and evolution》2012,29(3):1019-1029
Teneurins are type II transmembrane proteins expressed during pattern formation and neurogenesis with an intracellular domain that can be transported to the nucleus and an extracellular domain that can be shed into the extracellular milieu. In Drosophila melanogaster, Caenorhabditis elegans, and mouse the knockdown or knockout of teneurin expression can lead to abnormal patterning, defasciculation, and abnormal pathfinding of neurites, and the disruption of basement membranes. Here, we have identified and analyzed teneurins from a broad range of metazoan genomes for nuclear localization sequences, protein interaction domains, and furin cleavage sites and have cloned and sequenced the intracellular domains of human and avian teneurins to analyze alternative splicing. The basic organization of teneurins is highly conserved in Bilateria: all teneurins have epidermal growth factor (EGF) repeats, a cysteine-rich domain, and a large region identical in organization to the carboxy-half of prokaryotic YD-repeat proteins. Teneurins were not found in the genomes of sponges, cnidarians, or placozoa, but the choanoflagellate Monosiga brevicollis has a gene encoding a predicted teneurin with a transmembrane domain, EGF repeats, a cysteine-rich domain, and a region homologous to YD-repeat proteins. Further examination revealed that most of the extracellular domain of the M. brevicollis teneurin is encoded on a single huge 6,829-bp exon and that the cysteine-rich domain is similar to sequences found in an enzyme expressed by the diatom Phaeodactylum tricornutum. This leads us to suggest that teneurins are complex hybrid fusion proteins that evolved in a choanoflagellate via horizontal gene transfer from both a prokaryotic gene and a diatom or algal gene, perhaps to improve the capacity of the choanoflagellate to bind to its prokaryotic prey. As choanoflagellates are considered to be the closest living relatives of animals, the expression of a primitive teneurin by an ancestral choanoflagellate may have facilitated the evolution of multicellularity and complex histogenesis in metazoa. 相似文献
14.
Hirohiko Aoyama 《Development, growth & differentiation》1993,35(5):507-519
The ventro-medial wall of a somite gives rise to the sclerotome and then to cartilaginous axial skeleton, while the dorso-lateral wall differentiates into the dermomyotome to form dermal mesenchyme and muscle. Although previous studies suggested pluri-potency of somite cell differentiation, apparent pluri-potency may be the result of migration of predetermined cells. To investigate whether the developmental fate of any region is determined, I isolated fragments of a region of a quail somite and transplanted them into chick embryos. When a fragment of the ventral wall of a quail somite, the prospective sclerotome, was transplanted into a chick embryo between the ectoderm and a newly formed somite, the transplanted quail cells were shown to form myotome and mesenchyme in 4-day chimera embryos and to form muscle and dermal tissue in 9-day chimeras. On the other hand, when a fragment of the dorsal wall of a quail somite, the prospective dermomyotome, was transplanted into a chick embryo between the neural tube and a newly formed somite, the graft gave rise to mesenchyme around the neural tube and notochord and then to vertebral cartilage. Thus the developmental fate of a region of a somite was shown not to be determined at the time of somite segmentation, confirming previous observations. 相似文献
15.
Analysis of the binding of fluorescent C5a and C3a to human peripheral blood leukocytes 总被引:7,自引:0,他引:7
Fluorescein-labeled human C5a and C3a were prepared and utilized to analyze the binding of C5a and C3a to human neutrophils and mononuclear cells. The fluorescein derivatives of C5a (Fl-C5a) and C3a (Fl-C3a) contained approximately one fluorescein molecule per molecule of protein. Fl-C5a retained biologic activity as determined by neutrophil O2- production, enzyme release, receptor binding, and reaction with rabbit anti-C5a antibody. Fl-C3a was biologically active as measured by contraction of guinea pig ileal strips, and maintained 87% of its antigenic character when reacted with rabbit anti-human C3a. The binding of Fl-C5a and Fl-C3a to human neutrophils and mononuclear cells was assessed with the use of flow cytometry. Fl-C5a bound to greater than 90% of neutrophils, with an average ED50 ranging from 2.8 to 6.8 nM, depending on the method of analysis. Fl-C5a binding to neutrophils was specific and was not inhibited by the presence of formyl-methionyl-leucyl-phenylalanine (f-MLP), C3a, or casein. Fl-C5a binding was totally blocked by an excess of C5a. C5a des arg partially inhibited the binding of Fl-C5a to neutrophils, but was 1000-fold less effective than C5a. Similar experiments with mononuclear cells showed that Fl-C5a was bound by monocytes but not by lymphocytes. Fl-C5a binding to monocytes was blocked totally by C5a but not by C3a or f-MLP. Comparative binding studies with neutrophils, monocytes, and lymphocytes showed that Fl-C5a was bound by an average of 93% +/- 4 of neutrophils, 68% +/- 9 of monocytes, and 6% +/- 3 of lymphocytes. Fl-C3a did not show significant binding to neutrophils, monocytes, or lymphocytes. These studies demonstrate that fluorescein derivatives of C5a and C3a can be prepared with retention of biologic activity, and provide a means to evaluate the binding of C5a to individual cells. 相似文献
16.
Zhou HX 《Trends in biochemical sciences》2012,37(2):43-48
Association between signaling proteins and their cellular targets is generally thought to be highly specific (implicating a high association constant, K(a)) and, at the same time, transient or short-lived (corresponding to a high dissociation rate constant, k(d)). However, a combination of high K(a) and high k(d) would lead to a high association rate constant (k(a) = K(a)k(d)), which poses a problem because there is a limit to which k(a) can be increased, set by the diffusional approach to form the complex. In this Opinion article, I propose that having the signaling protein disordered before binding to the target provides a way out of this quandary. The intrinsic disorder of the signaling protein would decrease K(a) without sacrificing the specificity of the complex, and thus would allow k(d) to be increased to a range appropriate for signaling. 相似文献
17.
Identification of the domains required for direct interaction of the helicase-like and polymerase-like RNA replication proteins of brome mosaic virus. 总被引:6,自引:0,他引:6
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Brome mosaic virus is a positive-strand RNA virus whose RNA replication requires viral protein 1a, which has putative helicase and capping functions, and 2a, which has putative polymerase function. Since domains of related sequence are conserved in a wide range of plus-strand RNA viruses, analysis of 1a and 2a function should have applicability to many other viruses. We have recently demonstrated that 1a and 2a form a complex in vivo and in vitro. Using immune coprecipitation and mutant polypeptides made in reticulocyte lysates, we have now mapped both the 1a and 2a domains necessary for complex formation. The sequences needed to bind 2a map to the carboxy-terminal helicase-like domain of 1a. Truncated polypeptides containing this domain were able to bind to 2a, while several small insertions in the helicase-like domain disrupted binding. The sequence required for binding 1a lies within a 115-residue subset of the 2a N-terminal segment preceding the polymerase-like domain. Truncations or fusion polypeptides containing this segment can bind 1a. We also determined that highly purified 2a protein made in insect cells can form a complex with highly purified 1a helicase-like domain made in Escherichia coli, suggesting that no other factor is required to mediate 1a-2a interaction. Previous genetic analyses of 1a and 2a are consistent with this mapping and show that the newly defined 1a and 2a binding regions are required for RNA synthesis. The locations of these interacting regions are discussed with regard to models of viral replication and the evolution of positive-strand RNA virus genomes. 相似文献
18.
An extended exposure to repeated loading on fingertip has been associated to many vascular, sensorineural, and musculoskeletal disorders in the fingers, such as carpal tunnel syndrome, hand-arm vibration syndrome, and flexor tenosynovitis. A better understanding of the pathomechanics of these sensorineural and vascular diseases in fingers requires a formulation of a biomechanical model of the fingertips and analyses to predict the mechanical responses of the soft tissues to dynamic loading. In the present study, a model based on finite element techniques has been developed to simulate the mechanical responses of the fingertips to dynamic loading. The proposed model is two-dimensional and incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue was considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an invicid fluid, while its hydraulic permeability was considered to be deformation dependent. Two series of numerical tests were performed using the proposed finger tip model to: (a) simulate the responses of the fingertip to repeated loading, where the contact plate was assumed to be fixed, and the bone within the fingertip was subjected to a prescribed sinusoidal displacement in vertical direction; (b) simulate the force response of the fingertip in a single keystroke, where the keyboard was composed of a hard plastic keycap, a rigid support block, and a nonlinear spring. The time-dependent behavior of the fingertip under dynamic loading was derived. The model predictions of the time-histories of force response of the fingertip and the phenomenon of fingertip separation from the contacting plate during cyclic loading agree well with the reported experimental observations. 相似文献
19.
M M Kozlov 《Biophysical journal》1999,77(1):604-616
Dynamin is a GTPase playing an essential role in ubiquitous intra cellular processes involving separation of vesicles from plasma membranes and membranes of cellular compartments. Recent experimental progress (. Cell. 93:1021-1029;. Cell. 94:131-141) has made it possible to attempt to understand the action of dynamin in physical terms. Dynamin molecules are shown to bind to a lipid membrane, to self-assemble into a helicoidal structure constricting the membrane into a tubule, and, as a result of GTP hydrolysis, to mediate fission of this tubule (). In a similar way, dynamin is supposed to mediate fission of a neck connecting an endocytic bud and the plasma membrane, i.e., to complete endocytosis. We suggest a mechanism of this "pinchase" action of dynamin. We propose that, as a result of GTP hydrolysis, dynamin undergoes a conformational change manifested in growth of the pitch of the dynamin helix. We show that this gives rise to a dramatic change of shape of the tubular membrane constricted inside the helix, resulting in a local tightening of the tubule, which is supposed to promote its fission. We treat this model in terms of competing elasticities of the dynamin helix and the tubular membrane and discuss the predictions of the model in relation to the previous views on the mechanism of dynamin action. 相似文献
20.
The massive conversion of delta-aminolevulinic acid (ALA) to protochlorophyllide (Pchlide) and the massive conversion of chlorophyllide a (Chlide a) to chlorophyll a (Chl a) are two essential conditions for the ALA-dependent assembly of photosynthetic membranes in vitro. In this work, we describe the development of a cell-free system capable of the forementioned biosynthetic activities at rates higher than in vivo, for the first 2 h of dark-incubation. The cell-free system consisted of (1) etiochloroplasts prepared from kinetin and gibberellic-acid-pretreated cucumber cotyledons, and (2) cofactors and additives described elsewhere and which are needed for the massive conversion of ALA to Pchlide, (3) high concentrations of ATP, MgCl(2), and an isoprenol alcohol such as phytol, were required for the massive conversion of Chlide a to Chl a. An absolute and novel requirement of Mg(2+) for the conversion of Chlide a to Chl a was also demonstrated. In addition to the role of phytol as a substrate for the conversion of Chlide a to Chl a, the data suggested that this alcohol may also be involved in the regulation of the reactions between ALA and Pchlide. It is proposed that during greening, the conversion of Chlide a to Chl a may follow different biosynthetic rates, having different substrate and cofactor requirements, depending on the stage of plastid development. 相似文献