AR, Adenosine; IR, inosine; GR, guanosine; AdR, deoxyadenosine; AMP, adenosine-5′-monophosphate.
a) Native enzyme.
b) Activity was found but the Km value is not available.
5.6 Role of Purine Salvage in Plants
The importance of purine salvage has been demonstrated in plants as well as other organisms. Purine salvage enzyme-deficient mutants do not grow normally. This recycling pathway is not only energetically advantageous for nucleotide formation, but also the rapid turnover of nucleotides by the salvage reactions is essential for normal cellular growth and homeostasis. A further role of salvage enzymes is to catalyse the removal of purine bases and nucleosides which inhibit the flow of metabolites and cause toxicity. The salvage activity is closely associated with physiological events in plants. Onset of seed germination, cell division and growth, breaking dormancy, and recovery from several stresses all require purine nucleotides produced by these purine salvage reactions. Purine salvage activity associated with plant developmental and physiological events has been discussed in detail by Ashihara et al. (2018).
5.7 Summary
In plants purine bases are salvaged by phosphoribosyltransferases while purine nucleosides are salvaged by nucleoside kinases and NPT. Possible salvage routes of four purine bases, adenine, hypoxanthine, guanine, and xanthine, and six purine nucleosides, adenosine, inosine, guanosine, xanthosine, deoxyadenosine, and deoxyguanosine, are present in plants. Adenine and adenosine are the best substrates. The purine salvage mechanism in plants is different from what occurs in other organisms.
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