Glutamine Synthetase• Metabolic functions of glutamine:- donor of amino group- storage form of ammonia• Control of glutamine synthetase is highly important fornitrogen metabolism.• Mammalian glutamine synthetase is activated by α-ketoglutarate,which is a product of the oxidative deamination of glutamate.• Activated glutamate synthetase decreases concentration of ammonia, a toxic metabolite. This prevents accumulation ofammonia.
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Heme Biosynthesis• Heme, a complex of iron with porphyrin, is a component of manyproteins, e.g., hemoglobin, myoglobin, cytochromes. Heme issynthesized in the erythrocytes and in the liver.• All carbon and nitrogen atoms of the heme are derived from acetateand glycine. The heme anabolic pathway involves intermediates δ-aminolevulinicacid (ALA) and porphobilinogen(PBG).• Lead inhibits PBG synthase that converts ALA to PBG, and,by this way, causes accumulation of ALA in the blood.• ALA resembles neurotransmitter δ-aminobutyric acid (GABA).Lead poisoning is often accompanied by the psychosis.ALA: -OOC-CH2-CH2-C(O)-CH2-NH3+GABA: -OOC-CH2-CH2-CH2-NH3+