Inosine monophosphate dehydrogenase from porcine (Sus scrofa domestica) thymus: purification and properties

1. IMP dehydrogenase (EC 1.1.1.205) from porcine thymus glands has been purified to homogeneity. 2. The enzyme has a subunit MW of 57 kDa and an amino acid composition similar to those obtained from other normal and cancerous mammalian cells. 3. The apparent Km values at pH 8.0 for IMP and NAD+ are 7 and 16 microM, respectively. 4. GMP, XMP and AMP are competitive inhibitors towards IMP and Ki values of 50, 85 and 282 microM, respectively. 5. The effectiveness of nucleotides to protect inactivation by CI-IMP is IMP > GMP > XMP > AMP.