lecture 2a lehninger principles of biochemistry · lehninger principles of biochemistry fourth...
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Lehninger Principles ofBiochemistry
Fourth Edition
Chapter 22:Biosynthesis of Amino Acids,
Nucleotides, and Related Molecules
Copyright © 2004 by W. H. Freeman & Company
Lecture 2a
Lecture 2a: Nitrogen-fixation and entry of N
Net reaction:
N2 + 10 H+ + 8 e- + 16 ATP --> 2 NH4+ + 16 ADP + 16 Pi + H2
Nitrogenase reductase: 60 k dalton
Dimer, α2 , contains single 4 Fe - 4 S center
Dinitrogenase : 240K dalton
Tetramer, α2 β2 , contains Fe-Mo and S. (some use V instead ofMo).
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Reduction of N2 to 2 NH3involves e- transport.
Some features
a) 2 ATP’s/e-
b) Obligatory H2 evolved
c) At least 8 e- transferred
d) Source of electrons:ferredoxins orflavodoxins
e) Nitrogenase complex:dinitrogenase reductase+ dinitrogenase
Nitrogenase complex: Nase docks with Nase reductase to obtainthe e- which will be give to N. This enz is very O2 sensitive.
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Glutamate: source of amino groups for most amino acids.
NH4+ is assimilated into organism with Glu and Gln as critical
entry points
Assimilation of NH4 into Glu requires 2 rxns:
(1) Gln synthetase:
a) Glu + ATP --> glutamyl phosphate + ADP
b) glutamyl phosphate + NH4+ --> Gln + Pi + H+
Net:?
(2) α-k-Glutarate + Gln + NADPH +H+ --> 2 Glu + NADP+
Net of (1) and (2):
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