Abstract
Quantitative data are presented on the distribution of pteridines, primarily xanthopterin, leucopterin, erythropterin, and sepiapterin, in adults and developing pupae of the butterfly Colias eurytheme. The pteridine biosynthetic pathway in the developing wings of Colias has been studied by the use of radioactive precursors injected into whole pupae and incubated in Ringer's solution with excised, developing wings. By comparison of isotope incorporation, by pupae and isolated wings, from uniformly labeled adenosine- and guanosine-14C and guanosine-8-14C, it was concluded that Colias forms the pteridine ring from guanosine (or a phosphorylated derivative) with loss of the guanosine carbon atom 8. Pteridine interconversions were examined by studying the kinetics of isotope incorporation by the pteridines from uniformly labeled guanosine-14C immediately after its injection into whole pupae, and by studying the incorporation patterns obtained upon incubation of isolated wings with xanthopterin-14C, leucopterin-14C, and erythropterin-14C. The pteridine pathway is bipartite, one branch leading to position 6 side chain-bearing pteridines, the other leading to pteridines not alkylated at position 6. Within the latter branch, xanthopterin serves as precursor of leucopterin and erythropterin. The origins of position 6 side chain of sepiapterin and position 7 side chain of erythropterin were studied by incubation of isolated wings with radioactive pyruvate, malate, lactate, serine, threonine, and β-hydroxybutyrate. The results showed no incorporation into the sepiapterin side chain from any of these, but strong incorporation into the erythropterin side chain from pyruvate, malate, and lactate. In addition, sepiapterin made by Colias from uniformly labeled guanosine-14C was oxidized to 2-amino-4-hydroxypteridine-6-carboxylic acid, and the specific radioactivities of the parent compound and oxidation product were compared. The observed loss of specific activity agrees quantitatively with that expected if the sepiapterin side chain arises by modification of substitution on the initial pteridine position 6 side chain derived from guanosine ribose. The predictions of the alternative hypothesis of cleavage and replacement of the initial side chain are not compatible with the values observed. The present findings are discussed in relation to other recent work on pteridine biosynthesis.
Highlights
By comparison of isotope incorporation, by pupae and isolated wings, from uniformly labeled adenosine- and guanosine-14C and guanosine-8- 14C, it was concluded that Colias forms the pteridine ring from guanosine with loss of the guanosine carbon atom 8
Isoxanthopterin occurs in quantities less than 0.015 pmole per insect, and pterin and at least one other blue fluorescing pteridine occur in amounts barely detectable by fluores
Pterin 6-carboxylic acid does not accumulate from biosynthesis in this species, but is found as a decomposition product in small amounts in aged specimens
Summary
Expe&nental Animals-Wild, inseminated females of C.eurytheme were captured in Florida, Indiana, Mississippi, andTexas by the present writer and others (see ‘Acknowledgments”).Different geographic origin of stocks had no discernible effect on the properties studied in this work. Expe&nental Animals-Wild, inseminated females of C. eurytheme were captured in Florida, Indiana, Mississippi, and. Texas by the present writer and others (see ‘Acknowledgments”). Different geographic origin of stocks had no discernible effect on the properties studied in this work. The progeny of these animals and subsequent further descendants were reared on vetch (Vkia) as larval food plant, under controlled photoperiod conditions of 16 hours of light per day and at constant temperature of 27”. Adults were fed on honey diluted with water. Under these conditions, the egg to egg generation time was 21 to 22 days. Disease outbreaks necessitated re-establishment of stocks from time to time
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