Table 3.
Comparison of H-site residues in CjaGST A1-1, CjaGST A3-3, HsaGST A3-3, and EcaGST A3-3. The human and equine enzymes are the most efficient ketosteroid isomerases and have similar specific activities, suggesting that the structural differences in positions 111, 213, and 216 are without consequence. The H-site residues of CjaGST A3-3 match either one or the other of the most efficient orthologs with the exception of Thr208, the latter residue possibly responsible for the 3-fold lower specific activity. The H-site residues of the two marmoset enzymes differ in positions 111 and 213, of which the voluminous Phe111 in CjaGST A1-1 may interfere with steroid binding and explain the considerably lower ketosteroid isomerase activity.
| Residue | CjaGSTA1 | CjaGSTA3 | HsaGSTA3 | EcaGSTA3 |
|---|---|---|---|---|
| 10 | F | F | F | F |
| 12 | A | A | G | G |
| 14 | G | G | G | G |
| 15 | R | R | R | R |
| 107 | L | L | L | L |
| 108 | L | L | L | L |
| 110 | P | P | P | P |
| 111 | F | L | L | I |
| 208 | T | T | A | G |
| 213 | L | V | L | V |
| 216 | A | A | A | S |
| 220 | F | F | F | F |
| 222 | F | F | F | F |