Orotidine, isolation

The most important pyrimidine derivatives are those upon which biological organisms depend. Cytosine 1018 and uracil 1019 are found in ribonucleic acid (RNA) in the form of their ribonucleotides, cytidine 1020 and uridine 1021, while in deoxyribonucleic acid (DNA), cytosine and thymine 1022 are found in the form of their 2 -deoxyribonucleotides, 2 -deoxycytidine 1023 and thymidine 1024. 5-Methylcytosine 1025 is also found to a small extent (c. 5%) in human DNA in the form of its 2 -deoxyriboside 1026, and 5-(hydroxymethyl)cytosine-2 -deoxyriboside 1027 has also been detected in smaller amounts <2005CBI1>. Many variants of cytosine and uracil can be found in RNA including orotic acid 1028 in the form of its ribonucleotide orotidine 1029. Other pyrimidine derivatives to have been isolated from various biological sources include 2 -deoxyuridine 1030, alloxan 1031, and toxopyrimidine (pyramine) 1032 (Figure 2). 

Orotidine-5 -monophosphate was isolated by adding to the appropriate incubation mixtures antimetabolites which cause it to accumulate by blocking further steps of pyrimidine biosynthesis. 

To develop a homologous transformation system, we have isolated a pyrG mutant of A. nlger and the A. nlger pyrG gene (coding for the enzyme orotidine-5 -phosphate decarboxylase). 

Orotic acid riboside has been isolated by Michelson, Drell, and Mitchell from the culture medium in which a uridine-requiring Neuro-spora mutant was grown. The riboside, orotidine, has unusually great... 

The riboside of orotic acid, orotidine, was isolated subsequently from the culture medium of a uridine-requiring Neurospora mutant (350). Orotidine was readily split to orotic acid because of unusually great acid lability this offered a plausible explanation for previous failures to isolate a conjugated form of orotic acid from those natural sources that 3oelded the free acid (338, 342, 343). With the current knowledge of the individual steps in pyrimidine biosynthesis (Section VI, D, 2), it is likely that orotidine was derived from orotidylic acid (orotidine 5 -phosphate), and that a genetic block in the mutant organism prevented decarboxylation of oro-... 

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