Portal de Periódicos da CAPES

The Diphtheria Toxin-dependent Adenosine Diphosphate Ribosylation of Rat Liver Aminoacyl Transferase II

1970; Elsevier BV; Volume: 245; Issue: 3 Linguagem: Inglês

10.1016/s0021-9258(18)63376-9

1083-351X

Ronald S. Goor, Elizabeth S. Maxwell,

Neonatal Health and Biochemistry

Abstract Diphtheria toxin is known to catalyze a reversible reaction in which the adenosine diphosphate ribose moiety of NAD is transferred to aminoacyl transferase II, resulting in the concomitant loss of transferase activity in protein synthesis. Some general characteristics of the reaction are reported and a mechanism is proposed. The rate of the reaction is proportional to toxin, aminoacyl transferase II, and NAD concentrations, but, in the presence of excess NAD, the extent of the reaction is dependent only on the amount of aminoacyl transferase II present. ADP ribosylation occurs at all temperatures between 0–40° with a maximum at 20°. The adenosine diphosphoribosylaminoacyl transferase II bond is stable to heating at 90° for 15 min in 5% trichloracetic acid. The following random mechanism for the reaction is proposed on the basis of results from kinetic studies, use of inhibitors of the reaction and isotope exchange reactions, as well as our failure to find a partial reaction. A ternary intermediate composed of toxin, NAD, and aminoacyl transferase II is formed by a series of different binary reactions. The results support the participation of all combinations of binary reactions in the formation of the ternary complex. Toxin is bound to the adenosyl moiety of NAD, as well as to the transfer enzyme. Aminoacyl transferase II is bound to the NMN moiety of NAD. The proposed ternary intermediate consisting of toxin, aminoacyl transferase II, and NAD breaks down rapidly to the final products, adenosine diphosphoribosylaminoacyl transferase II, nicotinamide, and toxin.