Enzymatic properties of sialic acid binding lectin from Rana catesbeiana modified with a water-soluble carbodiimide in the presence of various nucleophiles

The anti-tumor activity of sialic acid binding lectin from Rana catesbeiana (cSBL) was increased by chemical modification with a water-soluble carbodi imide (EDC) in the presence of nucleophiles such as ethylenediamine and gly cine methylester. Investigations on ribonuclease (RNase) activities of the modified cSBLs were conducted to elucidate the fundamental mechanisms under lying enhancement of the anti-tumor activity conferred by these modificatio ns. The following three characteristics were observed with modification. (i ) RNase activity of the modified cSBL Nas enhanced towards double stranded RNA and RNA-oligo dA hybrids. The activity increase was observed even under physiologic ionic strength conditions; (ii) RNase activity of the modified cSBL towards single stranded RNA and poly U decreased, while the activity towards poly C was unaffected; (iii) the base preference of the B2 base rec ognition site of modified cSBL decreased for guanine. On the contrary, the preference for cytosine and adenine increased. This result may explain why the RNase activity towards poly C Nas not affected by EDC-modification as m entioned above.