A kedvencem: N¹-5'-phosphoribulosyl-formimino-5-aminoimidazole-4-carboxamide ribonucleotide !
The histidine biosynthetic pathway in
all plants and bacteria is novel in several respects.
Histidine is derived from three precursors (Fig. 21-17):
PRPP contributes five carbons, the purine ring of ATP
contributes a nitrogen and a carbon, and the second ring
nitrogen comes from glutamine. The key steps are the
condensation of ATP and PRPP (N-1 of the purine ring
becomes linked to the activated C-1 of the ribose in
PRPP) (step ① in Fig. 21-17), purine ring opening that
ultimately leaves N-1 and C-2 linked to the ribose (step
③), and formation of the imidazole ring in a reaction
during which glutamine donates a nitrogen (step ⑤). The
use of ATP as a metabolite rather than a high-energy
cofactor is unusual, but not wasteful because it
dovetails with the purine biosynthetic pathway. The
remnant of ATP that is released after the transfer of
N-1 and C-2 is 5-aminoimidazole-4-carboxamide
ribonucleotide, an intermediate in the biosynthesis of
purines (see Fig. 21-27) that can rapidly be recycled to
Lehninger-Nelson-Cox: Principles of Biochemistry, 708.o.
homeostasis : The maintenance of a dynamic steady state by regulatory mechanisms that compensate for changes in external circumstances. ___...
A dalai láma felhívása a világhoz. Az etika fontosabb a vallásnál Ez nagy mondás. A láma urat is meg kell hívnunk a rendünkbe !
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But in the period between meals, especially if prolonged, there is some degradation of muscle protein to amino acids ⑤. ...