| abstract |
Polypeptides are those of the structure shown schematically in the drawing, in which the amino acids indicated by their usual abbreviations are in the laevo-rotatory form; R1-R5 are the residues of L-lysine, L-asparagine, L-leucine, L-threonine and L-aspartic acid respectively, or R1 is arginine, R2 and R5 are glycine, R3 is isoleucine and R4 is serine; = signifies -S-S-linkages; and the arabic numerals indicate the sequence numbers of specific amino acid residues, starting from the N-terminal. The new polypeptides (designated SP1 and PS2) have a selective cytotoxic effect against animal cells in the S-phase but are inactive against normal cells in a contact inhibition state. They can thus be used as antitumour agents. They can also be used as agents for the detection and determination of viruses, since they are also cytotoxic to virus-infected cells. |