Effect of a single dose of beta,beta'-iminodipropionitrile in vivo on the properties of neurofilaments in vitro: comparison with the effect of iminodipropionitrile added directly to neurofilaments in vitro.

The biochemical properties of neurofilaments isolated from control and iminodipropionitrile-treated rats were compared with regard to autophosphorylation capacity, hydrolysis of ATP, and the formation of a viscous gel between filaments. Both preparations exhibited a similar polypeptide composition, and no covalent cross-linking between neurofilament subunits was induced by iminodipropionitrile in vivo. An ATPase activity, systematically present in all preparations, was unaffected by the administration of iminodipropionitrile to the rats. Conversely, the autophosphorylation of neurofilament subunits in vitro was significantly higher in preparations from iminodipropionitrile-treated rats than from control animals, with a marked increase of the phosphorylation of a high molecular weight neurofilament-associated protein. Iminodipropionitrile provoked a higher gelation capacity of neurofilaments as measured in vitro, with a lower critical concentration for the preparation from treated animals. A similar increased interaction was obtained with millimolar concentrations of iminodipropionitrile added to bovine neurofilaments in vitro, involving likely neurofilament-associated molecules, because the effect of the drug was lost after their extraction by 0.8 M KCl. These results support the hypothesis that iminodipropionitrile interferes with the neurofilament networks through a preferential interaction with the neurofilament-associated proteins, resulting in a change in their properties and consequently in an increased capacity of interaction between the polymers.