Porphobilinogen synthase, the first source of heme's asymmetry.
ABSTRACT Porphobilinogen is the monopyrrole precursor of all biological tetrapyrroles. The biosynthesis of porphobilinogen involves the asymmetric condensation of two molecules of 5-aminolevulinate and is carried out by the enzyme porphobilinogen synthase (PBGS), also known as 5-aminolevulinate dehydratase. This review documents what is known about the mechanism of the PBGS-catalyzed reaction. The metal ion constituents of PBGS are of particular interest because PBGS is a primary target for the environmental toxin lead. Mammalian PBGS contains two zinc ions at each active site. Bacterial and plant PBGS use a third metal ion, magnesium, as an allosteric activator. In addition, some bacterial and plant PBGS may use magnesium in place of one or both of the zinc ions of mammalian PBGS. These phylogenetic variations in metal ion usage are described along with a proposed rationale for the evolutionary divergence in metal ion usage. Finally, I describe what is known about the structure of PBGS, an enzyme which has as yet eluded crystal structure determination.
SourceAvailable from: Mathias O. Senge[Show abstract] [Hide abstract]
ABSTRACT: Chlorophylls are a fundamental class of tetrapyrroles and function as the central reaction center, accessory and photoprotective pigments in photosynthesis. Their unique individual photochemical properties are a consequence of the tetrapyrrole macrocycle, the structural chemistry and coordination behavior of the phytochlorin system, and specific substituent pattern. They achieve their full potential in solar energy conversion by working in concert in highly complex, supramolecular structures such as the reaction centers and light-harvesting complexes of photobiology. The biochemical function of these structures depends on the controlled interplay of structural and functional principles of the apoprotein and pigment cofactors. Chlorophylls and bacteriochlorophylls are optically active molecules with several chiral centers, which are necessary for their natural biological function and the assembly of their supramolecular complexes. However, in many cases the exact role of chromophore stereochemistry in the biological context is unknown. This review gives an overview of chlorophyll research in terms of basic function, biosynthesis and their functional and structural role in photosynthesis. It highlights aspects of chirality and symmetry of chlorophylls to elicit further interest in their role in nature.Symmetry 09/2014; 6(3):781-843. DOI:10.3390/sym6030781 · 0.92 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Abstract The present study investigated the protective potential of the polyphenols in pomegranate juice against the detrimental effects of lead exposure on the hematological system and antioxidant parameters of rat red blood cells. Forty adult male Sprague Dawley rats weighing about 300 g were allocated randomly to four groups: a control group that received normal food and water; a positive control group that received a daily dose of 2000 ppm lead (as lead acetate) in their drinking water for 5 weeks; a low treatment group that received a daily dose of 2000 ppm lead together with 30μl pomegranate juice (PJ; equivalent to 1050 μmol total polyphenols) by gavages for 5 weeks; and a high treatment group that received 2000 ppm lead and 60μl PJ (equivalent to 2100 μmol total polyphenols) daily for 5 weeks. The plasma lead level was significantly (p<0.001) decreased as the plasma copper and zinc levels were significantly increased (p<0.001) in rats received PJ. Significant increases (p<0.001) in red blood cell (RBC) and white blood cell (WBC) counts, and haemoglobin (Hb) and packet cell volume (PCV) were found in both PJ groups compared to the rats exposed to lead alone. Rats that received PJ in addition to lead showed erythrocyte glutathione and plasma ceruloplasmin levels and erythrocyte superoxide dismutase and catalase activities that were almost close to the control values. These observations indicated that treatment of rats with polyphenols might have produced amelioration in hematological system of rats exposed to lead, protecting the level of copper, zinc and antioxidants by against lead induced damage in blood cells. Keywords: Lead, polyphenols, pomegranate juice, oxidative stress, blood cell, ratRevista Romana de Medicina de Laborator 01/2012; 20(Nr.3/4):47-57. · 0.17 Impact Factor
Open Journal of Pathology 01/2013; 03(01):26-31. DOI:10.4236/ojpathology.2013.31005