Description

The pyrimidine nucleotide biosynthetic pathway was revealed by experiments with a mutant strain of Neurospora crassa. The six-reaction pathway involved in UMP synthesis was revealed when a pyrimidine-requiring strain was given orotate instead of uracil and cytosine, leading to normal growth. Subsequently, the pathway for synthesis of CTP from UMP via UTP was elucidated. In the de novo synthetic pathway of purine nucleotides, the purine base is synthesized using PRPP (phosphoribosyl diphosphate) as the foundation, whereas in the de novo synthetic pathway of pyrimidine nucleotides, the pyrimidine base is first completed and then the ribose-5-phosphate of PRPP is attached. This pathway is essentially common to most organisms, even in Thermus thermophilus.The fourth reaction to produce orotic acid from dihydroorotate uses fumaric acid or NAD+ or quinone as the electron acceptor; Thermus thermophilus is thought to use quinone, but the type of quinone has not been identified. Furthermore, although there are two types of enzymes involved in the seventh reaction that converts UMP to UDP: one that uses both CMP and UMP as substrates, and one that uses only UMP as a substrate, Thermus thermophilus has a UMP-specific type of enzyme.

References

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