ADP-ribosylation in adrenal glands: purification and characterization of mono-ADP-ribosyltransferases and ADP-ribosylhydrolase affecting cytoskeletal actin.

Mono-ADP-ribosylation in mammals is poorly understood. In this study, we purified four mono-ADP-ribosyltransferases and one ADP-ribosylhydrolase from rat adrenal medulla. The four purified mono-ADP-ribosyltransferases had molecular weights of 69,000 by gel filtration, pH optima of 8.0, and Kms for their action on NAD of about 20 microM. The four enzymes ADP-ribosylated to the alpha-subunit of heteromeric GTP-binding proteins. After tryptic digestion of alkylated actin mono-ADP-ribosylated by the purified mono-ADP-ribosyltransferases or botulinum C2 toxin, the two radioactive peptide patterns were identical. The purified ADP-ribosylhydrolase with mono-ADP-ribosylated actin as the substrate had a molecular weight of 61,000 on gel filtration, a pH optimum of 7.5, and a Km for mono-ADP-ribosylated actin of about 7 microM. The enzyme released ADP-ribose from ADP-ribosylated actin and the alpha-subunit of hetromeric GTP-binding proteins. Actin monomers mono-ADP-ribosylated by the four mono-ADP-ribosyltransferases did not form actin filaments after the addition of Mg2+. After release of ADP-ribose by ADP-ribosylhydrolase, actin filaments formed on the addition of Mg2+, suggesting that the polymerization and depolymerization of cytoplasmic actin the adrenal chromaffin cells may be regulated by mono-ADP-ribosylation.