Separate de novo and salvaje purine pools are involved in the biosynthesis of theobromine but not caffeine in leaves of Coffea arabica L.
In Coffea arabica leaves, the purine ring of theobromine (3,7-dimethylxanthine) and caffeine (1,3,7-trimethylxanthine) is provided by de novo purine biosynthesis (a) [exponente 14 C] glycine, [exponente 14 C] bicarbonate, and [exponente 14 C] formate were incorporated into inosine 5-monophosphate (IMP), sum of adenine nucleotides (A̳de), theobromine, and caffeine; and (b) incorporation of [exponente 14 C] formate into IMP, A̳de, theobromine, and caffeine was inhibited by azaserine, a known inhibitor of de novo purine biosynthesis. Capacity of coffee leaves to salvage added purines was demonstrated by incorporation of [exponente 14 C] hypoxanthine into A̳de and the incorporation of [exponente 14 C] adenosine, [exponente 14 C] adenine, [exponente 14 C] inosine, and [exponente 14 C] hypoxanthine into both theobromine and caffeine. Consistent with synthesis of theobromine from two separate purine nucleotide pools, one synthesized de novo and one via salvage, added xanthine 5-monophosphate (XMP), inosine, or hypoxanthine failed to reduce the incoporation of [exponente 14 C] formate into theobromine but diluted the specific radioactivity of [exponente 14 C] adenosine and [exponente 14 C] adenine incorporated into theobromine. Evidence that theobromine is not the inmediate precursor of caffeine is provided: (a) [exponente 14 C] xanthine was incorporated into caffeine but not into theobromine; (b) exogenous xanthine diluted the specific radioactivity of caffeine synthesized from [exponente 14 C] adenine and hypoxanthine but caused accumulation of radiolabel in theobromine; (c) allopurinol, a known inhibitor of the conversion of hypoxanthine to xanthine, reduced incorporation of [exponente 14 C] adenine and [exponente 14 C] hypoxanthine into caffeine but caused accumulation of radiolabel in theobromine; and (d) incorporation of [exponente 14 C] formate into caffeine, but not into theobromine, was reduced by added XMP, inosine, or hypoxanthine.
| Main Authors: | , |
|---|---|
| Format: | biblioteca |
| Published: |
1993
|
| Subjects: | COFFEA ARABICA, HOJAS, TEOBROMINA, CAFEINA, PURINAS, BIOSINTESIS, METABOLISMO, TECNICAS ANALITICAS, |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | In Coffea arabica leaves, the purine ring of theobromine (3,7-dimethylxanthine) and caffeine (1,3,7-trimethylxanthine) is provided by de novo purine biosynthesis (a) [exponente 14 C] glycine, [exponente 14 C] bicarbonate, and [exponente 14 C] formate were incorporated into inosine 5-monophosphate (IMP), sum of adenine nucleotides (A̳de), theobromine, and caffeine; and (b) incorporation of [exponente 14 C] formate into IMP, A̳de, theobromine, and caffeine was inhibited by azaserine, a known inhibitor of de novo purine biosynthesis. Capacity of coffee leaves to salvage added purines was demonstrated by incorporation of [exponente 14 C] hypoxanthine into A̳de and the incorporation of [exponente 14 C] adenosine, [exponente 14 C] adenine, [exponente 14 C] inosine, and [exponente 14 C] hypoxanthine into both theobromine and caffeine. Consistent with synthesis of theobromine from two separate purine nucleotide pools, one synthesized de novo and one via salvage, added xanthine 5-monophosphate (XMP), inosine, or hypoxanthine failed to reduce the incoporation of [exponente 14 C] formate into theobromine but diluted the specific radioactivity of [exponente 14 C] adenosine and [exponente 14 C] adenine incorporated into theobromine. Evidence that theobromine is not the inmediate precursor of caffeine is provided: (a) [exponente 14 C] xanthine was incorporated into caffeine but not into theobromine; (b) exogenous xanthine diluted the specific radioactivity of caffeine synthesized from [exponente 14 C] adenine and hypoxanthine but caused accumulation of radiolabel in theobromine; (c) allopurinol, a known inhibitor of the conversion of hypoxanthine to xanthine, reduced incorporation of [exponente 14 C] adenine and [exponente 14 C] hypoxanthine into caffeine but caused accumulation of radiolabel in theobromine; and (d) incorporation of [exponente 14 C] formate into caffeine, but not into theobromine, was reduced by added XMP, inosine, or hypoxanthine. |
|---|