The hydrolysis of adenylyl(3'→5')adenosine (ApA) and guanylyl(3'→5')adenosine (GpA) dinucleotides by the cytotoxic protein α-sarcin has been studied. Quantitative analysis of the reaction has been performed through reverse-phase chromatographic (HPLC) separation of the resulting products. The hydrolysis of the 3'-5' phosphodiester bond of these substrates yields the 2'-3' cyclic mononucleotide; this intermediate is converted into the corresponding 3'-monophosphate derivative as the final product of the reaction. The values of the apparent Michaelis constant (K(M)), k(cat) and k(cat)/K(M) have also been calculated. The obtained results fit into a two-step mechanism for the enzymatic activity of α-sarcin and allow to consider this protein as a cyclizing RNase.
Lacadena, J., Martínez Del Pozo, A., Lacadena, V., Martínez-Ruiz, A., Mancheño, J. M., Oñaderra, M., & Gavilanes, J. G. (1998). The cytotoxin α-sarcin behaves as a cyclizing ribonuclease. FEBS Letters, 424(1–2), 46–48. https://doi.org/10.1016/S0014-5793(98)00137-9