The generalization of pre-neocarzinostatin and antagonism of neocarzinostatin-induced DNA scission in vitro.

Pretreatment of the antitumor protein neocarzinostatin with heat, ultraviolet or white light, and thiols inactivates the drug, as measured by the cessation of phage T2 DNA strand scission in vitro. The inactive forms obtained are identical with pre-neocarzinostatin on the basis of isoelectric focusing, molecular weight determination, and changes in circular dichroism spectra. In incubations together with neocarzinostatin and T2 DNA, the inactive form inhibits strand scission to a considerable degree. This result suggests that both forms compete for a limited number of available DNA binding sites.