Table II.
Effect of amino acids and substrates on the protection of GS inactivation by MCO
| Addition | GS Inactivation |
|---|---|
| % of control | |
| Control | 100% |
| Arg | 92.5 ± 1.9 |
| Cys | 45.6 ± 2.9 |
| Glu | 95.4 ± 1.5 |
| Gln | 69.6 ± 3.9 |
| GSH | 104.0 ± 2.8 |
| His | 55.7 ± 1.7 |
| Leu | 93.0 ± 3.3 |
| Lys | 108.2 ± 2.2 |
| Phe | 81.6 ± 1.1 |
| Pro | 87.5 ± 0.6 |
| Trp | 91.5 ± 1.6 |
| Tyr | 85.9 ± 5.2 |
| ATP | 53.6 ± 1.2 |
| Glu/ATP | 38.1 ± 2.0 |
| MgCl2 | 54.2 ± 3.7 |
| MnCl2 | 27.7 ± 4.3 |
A 4-d-old root extract (desalted ammoniun sulfate fraction) was incubated in 50 mm imidazol (pH 7.4) with 5 mm amino acids and GS substrates before the addition of a mixture of FeCl3 and DTT with or without EDTA for 40 min of incubation at 4°C for partial inactivation (Fig. 1). Samples were assayed for transferase activity following incubation in the MCO system. Inactivation was calculated as the difference between each sample and its respective control in which 1 mm EDTA was added. Values are the percentages of inactivation compared with the nonprotected sample. Values below 100% = protection from inactivation; values close to 100% = no protection. Data are the averages ± se of at least three independent experiments (n ≥ 3).