Three forms of Candida utilis ribose 5-phosphate ketol isomerase

Three forms (I, II, and III) of R 5-P ketol icomerase (EC 5.3,1.6) were separated and purified from Candida utilis. The Kms for R 5-P by I, II, and III were 0.77 mM, 0.67 mM and 0.16 mM, respectively. The isoelectric points of the forms, I, II, and III were 3.79, 3.87 and 3.99, respectively.The activation energies of the forms, I, II, and III were 10,800, 12,000 and 6360 cal/mole, respectively. The forms, I, II, and III were all inhibited with chelating reagent, EDTA (1 mM), but not affected with thiol reagents such as p-CMB, ICH2COOH, NEM, and DTNB. These properties are quite different from the other known R 5-P ketol isomerases, all of those are not affected with EDTA, but inhibited with the thiol reagents as described above.