Subcellular distribution of mono(ADP-ribose) protein conjugates in rat liver

Rat liver nuclei isolated by neutral sucrose or citric acid procedures contain < 5 % of the total mono(ADP-ribosyl) proteins found in the corresponding homogenates. The extra-nuclear location of these conjugates is not a consequence of artifacts like leakage or selective degradation during isolation of nuclei. Comparably low levels of mono(ADP-ribosyl) proteins were also found in the nuclei of mouse kidney, and of Ehrlich ascites tumor cells although the latter also had low conjugate levels in non-nuclear compartments. Fractionation of liver tissue revealed that most of the NH 2OH-resistant mono(ADP-ribosyl) protein conjugates were associated with the mitochondrial fraction, and, to a small degree, with the plasma membranes. The NH 2OH-sensitive conjugates were primarily found in the fractions containing the endoplasmic reticulum. This distribution is in accordance with multiple and independent functions of mono ADP-ribosylation and poly ADP-ribosylation reactions.