ACTIVE FORM OF PSEUDOMONAS-MEVALONII 3-HYDROXY-3-METHYLGLUTARYL COENZYME-A REDUCTASE

Based on multiple gel permeation chromatographic experiments, we repor t a Stokes radius of 59.7 Angstrom for Pseudomonas mevalonii 3-hydroxy -3-methylglutaryl coenzyme A reductase (HMG-CoA reductase; EC 1.1.1.88 ) and its His381Asn, His381Gln, and His381Lys mutant enzymes. Comparis on of this Stokes radius with the radius calculated from the crystal s tructure indicated that the active form of P. mevalonii HMG-CoA reduct ase was a hexamer and not a dimer as previously thought. The Stokes ra dius, an S-20,S-w of 11.0, and an estimated (V) over bar of 0.723 were used in the Svedberg equation to calculate an anhydrous molecular mas s of 270,084 Da for P. mevalonii HMG-CoA reductase (monomer mass 45,53 8 Da), consistent with the enzyme being a hexamer in solution. The Sto kes radii of all standard proteins examined correlated with the invers e error function complement of their partition coefficient, K-d. K-d d id not correlate with logarithm of the standard protein's molecular we ight. Eight nonstandard proteins had Stokes radii that matched their c rystallographic radii of longest axis. This indicated that the frozen conformation of a protein in its crystal form can dictate restraints o n its shape in solution. (C) 1997 Academic Press.