This chain type is frequently found in several lipid forms, either isolated or combinedwith other chemical structures. A series of long-chain methylated alkanes (more than 23carbon atoms), saturated or with one double bond, were identified in settlingparticles and surface sediments from Japanese lakes and were shown to beproduced by planktonic bacteria being thus useful molecular markers (). Laboratory experiments havedemonstrated that -alkanes up to C35 may be formed in the laboratoryunder hydrothermal conditions (Fischer-Tropsch-type reactions) from formic acidor oxalic acid ().These results support the theory of the origin of life in hydrothermal systems.
Methoxyalkanes have been identified on bodies or silk of spiders :1-methoxy-16,20,24,28-tetramethylhentriacontane and1-methyl-2,24-dimethyloctacosane ().
It must be noticed that highly branched and unsaturated (2-5 double bonds)isoprenoids are widespread components in marine sediments (review by). The identification of C25 and evenof C30 highly branched isoprenoid alkenes in diatoms () have clearly established that they are the source ofthese compounds found in sediments.
Among the saturated isoprenoids found in geological sediments and oils, the mostfrequent are pristane (2,6,10,14-tetramethylpentadecane) and phytane (2,6,10,14-tetramethylhexadecane). Both compounds can be generateddiagenetically from the phytol side chain of chlorophyll. Pristane may alsoderive from the side chain of tocopherols while phytane is also generated byArchaea.
Chloroplast ATP synthase and the enzyme from some photosyntheticbacteriahave 2 different, although similar, -typesubunits in the protontranslocating FO portion, namely and, one copy ofeach.
High homology is found for most of the ATP synthase subunits fromdifferentbacteria and chloroplasts.
Mitochondrial enzyme is much more complex; are described at the moment. Some of these subunits have high homology to bacterial andchloroplast counterparts, especially subunits Alpha, Beta and Gamma inthe F1 portion and subunits and in the FOportion. Many subunits are unique for the mitochondrial enzyme (see for details).However, the catalytic and proton translocating "core" of the enzyme isstill highly homological to that of bacterial and chloroplast ATPsynthase. The overall topology of the enzyme is also quite similar.
F214_Photosynthesis and Respiration…
A series of 34 3-benzyl-5-(arylmethylene)furan-2(5)-ones, designed using the naturally occurring toxins nostoclides as a lead structure, was synthesized as potential inhibitors of the photosynthetic electron transport. All compounds were fully characterized by IR, NMR (1H and 13C), and MS spectrometry. HMBC and HSQC bidimensional experiments allowed 13C and 1H assignments. Their biological activities were evaluated in vitro as the ability to interfere with light-driven reduction of ferricyanide by isolated spinach chloroplasts. About two-thirds of the compounds exhibited inhibitory properties in the micromolar range against the basal electron flow from water to K3[Fe(CN)6]. The inhibitory potential of these 3-benzyl-5-(arylmethylene)furan-2(5)-one lactones is higher than that of other nostoclide analogues previously synthesized in the same laboratories.
Lead toxicity in plants - SciELO
Protoporphyrinogen oxidase (PPO) is an enzyme in the of the plant cell that oxidizes protoporphyrinogen to produce IX. This product is important because it is a precursor molecule for both chlorophyll (needed for photosynthesis) and heme (needed for chains) (Figure: Protoporphyrin lX). However, inhibitors of the oxidase enzyme do more than merely block the production of chlorophyll and heme. When the enzyme is inhibited, the protoporphyrinogen substrate accumulates and is slowly oxidized by the high concentrations of O2 being produced in the chloroplast, producing protoporphyrin IX. This spontaneous production of the product may seem to bypass the inhibitor and let the cell function normally, but it has dire consequences.
Protoporphyrin is a very effective photosensitizing molecule. Normally, the concentrations of protoporphyrin in the cell are kept very low and it is channeled from its production site in the chloroplast to other locations in the cell where it is needed for heme biosynthesis. In the presence of the herbicide inhibitors, the concentrations of protoporphyrin increase and begin to accumulate throughout the cell. As with most of the herbicides discussed in this course, if the plant is maintained in the dark or in dim light, the effects of the herbicide are not observed. However, when exposed to light the protoporphyrin released in the cell is excited to the with a high efficiency and interacts with molecular O2 to produce singlet oxygen. Singlet oxygen is toxic to cells because it is much more destructive than molecular oxygen in the normal triplet state. Favorite targets of singlet oxygen include the double bonds of fatty acids and amino acids. Membranes, sites with high concentrations of unsaturated fatty acids, are particularly vulnerable to peroxidation (molecular damage from free radicals). The plasma membrane of the plant cell is considered to be the vulnerable component most impacted by the photodynamic damage from herbicides that inhibit protoporphyrinogen oxidase. Here is a velvetleaf plant that has been sprayed with Blazer, a PPO inhibitor (Figure: Blazer Damage). Notice the necrotic (localized dead tissue) lesions that have formed in response to the herbicide. Inhibition of PPO has caused release of protoporphyrin throughout the plant cell. In the presence of light singlet oxygen is produced, causing rapid cell death.