| Popis: |
1. 1. Although the levels of ALA-S in photosynthetic (Ph) are higher than in aerobic (A) cells, physical and kinetic properties are similar. Optimum reaction pH is 7.5; maximal product formation occurs at 37°C. 2. 2. The enzyme has an absolute requirement for glycine. The addition of cysteine (CySH), glutathione (GSH), cystine or 2-mercaptoethanol to the reaction mixture does not greatly modify activity, instead it diminishes in the presence of ALA, indicating that the ALA-feedback inhibits its own synthesis. 3. 3. The enzyme is not stable when stored at −15°C; however, activity remains constant for at least 18 hr when different preparations are kept at 0–4°C. 4. 4. Evidence of the existence of one or two low molecular weight compounds which stimulate or stabilize ALA-S activity was found by dialysis of crude extracts. 5. 5. K m values for glycine, succinyl-CoA and pyridoxal phosphate were 1.5 x 10 −2 M, 1 x 10 −5 M and 1 x 10 −6 M respectively. 6. 6. Molecular weight was estimated to be 61 65,000 and no indication of active higher molecular weight species or subunits was obtained. 7. 7. Activity of R. palustris ALA-S can be efficiently regulated within the cell by the formation of one or two low molecular weight factors, depending on growth conditions and also through the levels of both glycine and ALA. |
