The pathway, the whole pathway, and nothing but the pathway.
CPSII is inhibited by UTP and purine nucleotides, but is activate by PRPP.
PRPP synthase converts Ribose 5 Phosphate to phospho-ribosyl-pyrophosphathe, needs magnesium and ATP
Aspartate transcarbamoylase is inhibited by CTP but actived by ATP
CAA is converted to DHOA by dihydroorotase
DHOA must be shuttled from the cytoplasm into the mitochondria to be reduced by dihydroorotate dehydrogenase to form orotic acid.
Orotic acid is then shuttled out of the mitochondria and converted to orotidine monophosphate. PRPP is needed, taken from initial steps of purine synthesis.
Deficiency in NADPH production could affect ribonucleotide reductase: glucose-6-phosphate DH, gluconate DH, malate DH, isocitrate DH.
Deficiency of B12/ B6 / B9 / Zinc can cause the inability to produce TMP