Table II.
Catalytic activity and kinetic properties of the p.R369C mutant
| Wild-type CBS | p.R369C mutant | |
|---|---|---|
| Specific activity in crude extracts (nmol cystathionine/mg total cellular protein/hour)⁎ | ||
| E. coli 37° C | 142.7 ± 27.2 | 2.8 ± 2.2 |
| E. coli 18° C | 85.5 ± 27.0 | 13.1 ± 0.4 |
| CHO-K1 37° C | 111.1 ± 39.7 | 71.2 ± 27.3 |
| Relative activity in crude extracts (specific activity corrected for tetramer abundance, in % of wild-type enzyme) | ||
| E. coli 37° C | 100% | 34% ± 26% |
| E. coli 18° C | 100% | 67% ± 8% |
| CHO-K1 37° C | 100% | 54% ± 24% |
| Kinetic properties of wild-type and p.R369C mutant enzyme in crude extracts after expression in CHO-K1 cells† | ||
| Km serine (mmol/L) | 10.1 | 8.1 |
| Km homocysteine (mmol/L) | 5.8 | 7.5 |
| Vmax (nmol/h/mg total cellular protein/) | 1715 | 500 |
| Normalized Vmax (nmol/h/arbitrary units of CBS tetramer) | 100% | 55% |
⁎
Numbers shown are means of 3 independent expression experiments with SD.
†
Numbers shown are means of 2 independent experiments (with the exception of Km for homocysteine, which was determined only once).