COFACTOR REQUIREMENT OF RIBOSOME-INACTIVATING PROTEINS FROM PLANTS

A large number of type 1 ribosome-inactivating proteins (RIPs) from pl ants (families of Caryophyllaceae, Cucurbitaceae, Euphorbiaceae, Phyto laccaceae, and Poaceae) were examined for their requirement for ATP an d supernatant factors for full activity. A marked requirement was obse rved with agrostin among Caryophyllaceae, gelonin among Euphorbiaceae, and with both barley RIP and tritin-S among Poaceae, The distribution of cofactor requirement in Phytolaccaceae discriminates leaf forms (c ofactor-independent) from seed and root forms (cofactor-dependent). Th e results are discussed on the basis of the present knowledge on the t issue localization of RIPs and on the sensitivity of ribosomes to cons pecific RIPs.