Feb 5, 1976

Mechanism and stereochemistry of enzymic reactions involved in porphyrin biosynthesis

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
M AkhtarZ Zaman

Abstract

5-Aminolaevulinate synthetase cataylses the condensation of glycine and succinyl-CoA to give 5-aminolaevulinic acid. At least two broad pathways may be considered for the initial C--C bond forming step in the reaction. In pathway A the Schiff base of glycine and enzyme bound pyridoxal phosphate (a) undergoes decarboxylation to give the carbanion (b) which then condenses with succinyl-CoA with the retention of both the original C2 hydrogen atoms of glycine. In pathway B, loss of a C2 hydrogen atom gives another type of carbanion (c) that reacts with succinyl-CoA. Evidence has been presented to show that the initial C--C bond forming event occurs via pathway B which involves the removal of the pro R hydrogen atom of glycine. Subsequent mechanistic and stereochemical events occurring at the carbon atom destined to become C5 of 5-aminolaevulinate have also been delineated.(Carticle) Several mechanistic alternatices for the formation of the two vinyl groups of haem from the propionate residues of the precursor, coproporphyrinogen III, have been examined. (see article). It is shown that during the biosynthesis both the hydrogen atoms resident at the alpha positions of the propionate side chains remain undisturbed thus eliminating mec...Continue Reading

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Mentioned in this Paper

Porphobilinogen
Molecular Stereochemistry
Biochemical Pathway
Acrylic Acid
Positioning Attribute
Atom (substance)
Glycine, Monopotasssium Salt
Natrix natrix (reptile)
Coproporphyrinogen III
Succinates

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