HIGH RESOLUTION CRYSTAL STRUCTURE OF PI DELTA-5-3-KETOSTEROID ISOMERASE MUTANTS Y30F/Y55F/Y115F/ D38N (Y32F/Y57F/Y119F/D40N, PI NUMBERING)COMPLEXED WITH EQUILENIN AT 2.1 A RESOLUTIONHIGH RESOLUTION CRYSTAL STRUCTURE OF PI DELTA-5-3-KETOSTEROID ISOMERASE MUTANTS Y30F/Y55F/Y115F/ D38N (Y32F/Y57F/Y119F/D40N, PI NUMBERING)COMPLEXED WITH EQUILENIN AT 2.1 A RESOLUTION