This document summarizes the enzymatic pathway of purine biosynthesis. Purines are biologically synthesized as nucleotides, particularly as bases attached to ribose-5-phosphate. The key purines synthesized are adenine and guanine. The pathway involves multiple enzyme-catalyzed steps beginning with 5-phosphoribosyl-1-pyrophosphate. Most enzymes involved are transferases or ligases. Amido phosphoribosyltransferase is the rate-limiting enzyme, which is regulated by feedback inhibition by purine nucleotides.

1. ENZYMATIC PATHWAY OF
PURINE BIOSYNTHESIS
Submitted By -
SUNIL KUMAR SAHOO

2. CONTENTS
• INTRODUCTION
• PURINE BIOSYNTHETIC PATHWAY
• ENZYMES INVOLVED IN THE PATHWAY
• UNIQUENESS OF THE ENZYMES INVOLVED
• CONCLUSION
• REFERENCES

3. INTRODUCTION
• Purines are biologically synthesized as nucleotides
and in particular as ‘ribotides’ i.e., bases attached to
ribose-5-phosphate.

4. • The two important purines are ‘ADENINE’ and
‘GUANINE’.
5-Phosphoribosyl-1-pyrophosphate (PRPP)
provides the foundation on which the bases
are constructed step by step.

5. FIG: PURINE BIOSYNTHETIC PATHWAY

7. SYNTHESIS OF AMP & GMP

13. UNIQUENESS OF THE
ENZYMES INVOLVED
• In purine biosynthetic pathway, most of the
enzymes involved belong to class II
TRANSFERASES and class VI LIGASES.
• The two transformylase enzymes involved in
purine biosynthesis require 10-formyl-
H4folate as a cofactor, but can utilize
efficiently different synthetic analogs like 5-
aminoimidazole.

14. • Amido phosphoribosyltransferase (E.C.
2.4.2.14) is the rate-limiting enzyme in purine
biosynthesis pathway.It is regulated by
feedback inhibition by purine nucleotides,
IMP, GMP and AMP and this feedback
inhibition is reversed by PRPP.
• Increased quantities of intracellular PRPP lead
to overproduction of purine synthesis and of
uric acid.
• Hence, for balanced production of purines,
interconversion of IMP to AMP and GMP are
under feedback control.

15. CONCLUSION
• It can be concluded that the purine biosynthetic
pathway is a multienzyme process pathway
where every step of the reaction is catalysed by a
specific enzyme.
• Purines are deaminated with the amino group
released as ammonia, to xanthine.Most of the
ammonia will be transported to liver as
glutamate for ultimate excretion as urea.
• Since the purine ring is excreted intact, no energy
benefit is received to man from these carbons.

16. REFERENCES
• Hartman, S.C. And Buchanan, J.M.
Biosynthesis of the purines XXI. 5-
Phosphoribosylamidotransferase. J. Biol.
Chem. 233(1958) 451-455.
• Parker, J. Identification of the PurC gene
product of E.coli. J. Bacterial 157(1984)712-
717.
• Lehninger
• www.sbcs.qmul.ac.uk/iubmb