Biosynthesis of 1-methyladenine by isolated segments of starfish ovaries.
Acid-soluble 1-methyladenine (1-MeA) and an insoluble fraction containing 1-MeA were formed when radioactive L-methionine or adenine (A) were incubated with starfish ovary segments. Attempts to prepare free ribonucleic acid (RNA) from ovaries failed since it was strongly bonded to protein as ribonucleoprotein (RN-P) which was therefore used in studies involving RNA. Incubation of ovary segments with [8-14C]adenine-8 (A-8-14C) yielded both soluble 1-Me-A-8-14C and RN-P-8-14C, and similar incubation with L-[methyl-14C]methionine yielded soluble 1-MeA-14CH3 and RN-P-14CH3. Hydrolysis of RN-P-8-14C with 1 N HCl at 100 degrees yielded 91% of the initial radioactivity in the purine fraction, and of this 90% was in A, 9% in 1-MeA, and 1% in 4(5)-amino-5(4)-imidazole carboxamidine (AIMCAD). With RN-P-14CH3 the corresponding figures were 20, 45, 27, and 28%. Degradation of 1-MeA-8-14C or RN-P-8-14C with 6 N HCl at 110 degrees yielded radioactive AIMCAD which, on heating at pH 12, gave radioactive 4(5)-amino-5(4)-imidazole carboxamide (AICA). When 1-MeA-14CH3 or RN-P-14CH3 were similarly degraded, radioactive AIMCAD was formed, but the AICA possessed little or no radioactivity due to the loss of the radioactive methyl group. Addition of radial nerve factor ( GSS) increased the yield of 1-MeA up to 19 times when radioactive L-methionine was substrate, but was ineffective with radioactive A. S-[8-14C]Adenosylmethionine was only about 3% as effective as L-[methyl-14C]methionine in supporting formation of 1-MeA, and its slight activity was not enhanced by GSS. Immature ovary segments were much more active than those from mature ovaries in synthesizing 1-MeA. The results support the contention that formation of free 1-MeA in starfish ovarian tissues involves methylation of adenine residues in a polynucleotide followed by liberation of 1-MeA by enzymatic hydrolysis.[1]References
- Biosynthesis of 1-methyladenine by isolated segments of starfish ovaries. Tarr, H.L. Gen. Comp. Endocrinol. (1985) [Pubmed]
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