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 !
"Some proteins endow cells and organisms with the ability to contract, to change shape, or to move about. Actin and myosin function...
We begin in each case by considering the covalent structure of the simple subunits (amino acids, fatty acids, monosaccharides, and nucleoti...