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Biosynthesis of Amino Acids:- Histidine Biosynthesis Uses Precursors of Purine Biosynthesis

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  851

2026-07-04

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Biosynthesis of Amino Acids:- Histidine Biosynthesis Uses Precursors of Purine Biosynthesis

The pathway to histidine in all plants and bacteria differs in several respects from other amino acid biosyn thetic pathways. Histidine is derived from three pre cursors (Fig. 1): PRPP contributes five carbons, the purine ring of ATP contributes a nitrogen and a carbon, and glutamine supplies the second ring nitrogen. The key steps are condensation of ATP and PRPP, in which N-1 of the purine ring is linked to the activated C-1 of the ribose of PRPP (step 1 in Fig. 1); purine ring opening that ultimately leaves N-1 and C-2 of adenine linked to the ribose (step 3); and formation of the imidazole ring, a reaction in 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-carbox amide ribonucleotide (AICAR), an intermediate of purine biosynthesis  that is rapidly re cycled to ATP.