| Autor: |
Duhaiman, Ali S., Rabbani, Nayyar |
| Zdroj: |
Biochemical and Biophysical Research Communications; April 1996, Vol. 221 Issue: 2 p229-233, 5p |
| Abstrakt: |
Chemical modification studies were performed to elucidate the role of cystiene residues in the catalytic activity of camel lens ζ-crystallin. 5,5′-dithiobis (2-nitrobenzoicacid) (DTNB) titration of the camel lens ζ-crystallin revealed that it contained 3 SH-groups and a disulfide bridge per subunit. One of the three SH-groups was readily accessible, whereas the other two were buried. Inactivation of ζ-crystallin by DTNB was caused by a modification of one cysteine residue per subunit. The resulting DTNB-modified enzyme was reactivated by dithiothreitol (DTT) or KCN. The inactivation was partially protected by NADPH, whereas 9,10-phenanthrenequinone (PQ) enhanced the modification of the enzyme. These results indicate that the SH- group being modified is located at/near the NADPH binding site which is not essential for catalysis. Incubation of the enzyme with DTT led to a substantial loss of the enzyme activity. However, DTT inhibition was prevented completely by preincubation of enzyme with PQ but not by NADPH indicating that an essential disulfide-bridge is present at the substrate binding site of ζ-crystallin. |
| Databáze: |
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