a group of natural nitrogenous heterocyclic compounds having a purine-type molecular structure. The structure of purine is

Both in the free state and as constituents of more complex compounds, purines play a key role in the life processes of all organisms. For example, the composition of nucleic acids includes the purine compounds adenine (6-aminopurine) and guanine (2-amino-6-oxypurine) and in some cases includes smaller quantities of methylated adenines, such as 6-methylamino-purine. In ribonucleic acids (RNA), the purine compounds are combined with ribose by a glycoside bond, and in deoxyribonucleic acids (DNA), with deoxyribose by a bond to the nitrogen atom in the 9 position of purine. The content of purines in DNA is equal to that of the pyrimidine bases, while in RNA the amount of purines is usually higher than that of the pyrimi-dines. In nucleic acids, both the purine and pyrimidine compounds effect the coding of hereditary information and its replication during protein biosynthesis.

Nucleotides containing adenine play an important role in bioenergetics; adenosine triphosphate (ATP), for example, is a universal participant in the energy exchange that occurs in living cells. Guanosine triphosphate is necessary for the realization of protein biosynthesis. Cyclic adenosine 3′: 5′-mono-phosphate (cyclic AMP) is an important link in the hormonal regulation mechanism. Purine compounds are also included in the composition of many coenzymes.

Examples of purine compounds are caffeine (contained in coffee and tea), theobromine (contained in the seeds of the cacao tree), hypoxanthine, and xanthine. In higher organisms, the synthesis of purine compounds, in nucleotide form, is effected mainly in the liver; inosine monophosphate serves as a universal intermediate during the final stages of this process. The degradation of purine compounds in various groups of organisms leads to the formation of various final products, such as uric acid, allantoin, and urea.