Aspartokinase of Rhodopseudomonas spheroides. Regulation of enzyme activity by aspartate beta-semialdehyde.

摘要: Abstract 1. The enzyme aspartokinase has been purified about 240-fold from extracts of the photosynthetic bacterium Rhodopseudomonas spheroides. An absolute requirement for adenosine triphosphate and a divalent cation activity shown. No other nucleoside phosphates can serve as phosphate donor; Mn++ replace Mg++. Potassium ion stimulates phosphorylation reaction by increasing maximal velocity facilitating binding an additional ATP molecule per enzyme. 2. None end product amino acids aspartic family, namely, lysine, methionine, threonine, or isoleucine, any combination these regulatory effect on activity. However, is strongly inhibited aspartate β-semialdehyde, key intermediate synthesis noted. inhibition competitive with respect to both ATP. It concluded that feedback β-semialdehyde R. spheroides provides effective mechanism in regulating biosynthesis four important acids. 3. Results heating experiments show several acids, particularly lysine protect against heat inactivation, indicating sites molecule. suggested that, contrast bacterial aspartokinases, although bound enzyme, have lost ability "interact" catalytic sites, thus are unable modify