ABSTRACT. To obtain biologically active substances that are useful in the study of cell structures and functions, we examined several biological activities of an extract of silkworm faeces with hot buffer. Wedetected a lectinlike substance in the extract and purified it. Whenthe extract of silkworm faeces was added to a culture of quail myoblasts transformed with temperaturesensitive Rous sarcoma virus (QM-RSVcells), the plated cells which were cultured at 35.5°C (the permissive temperature for RSVthat suppresses myogenic differentiation) became detached from the dishes and the cells in suspension aggregated. However, when the same amount of extract was added to plated QM-RSV cells cultured at 41°C, which is a nonpermissive temperature for RSV, the cells did not become detached. Other kinds of plated cells examined also did not become detached. Unlike plated cells, nonplated cells of all kinds aggregate in suspensionuponthe addition of the extract. This active substance was purified by monitoring its induction of cell aggregation. The purified substance was found to be a lectinlike glycoprotein with an apparent molecular mass of about 60 kDa. Further studies showed that the binding sites of this glycoprotein are sugar chains on the cell surface and that mannoseis an epitope.

In previous studies a novel lectin‐like glycoprotein was isolated from silkworm faeces and shown to recognize sugar chains, especially mannose on the cell surface as an epitope, and to cause aggregation of various types of cells in suspension. However, this substance caused detachment and aggregation of only some types of plated cells, such as QM‐RSV cells, which are quail myoblasts transformed with a temperature‐sensitive mutant of Rous sarcoma virus (ts‐RSV) at 35.5 °C, a permissive temperature for RSV. As described here, during studies on the mechanism of cell detachment and aggregation of QM‐RSV cells by this new lectin, some novel biological activities of the lectin were recognized. This lectin was found to bind to immunoglobulins (Ig) specifically at specific amino acid sequences, not via recognition of their molecular conformation. It also recognized the neural cell adhesion molecule (NCAM), which is one of the members of the Ig‐superfamily that have Ig‐like domains. Furthermore, it had a strong mitogenic effect on lymphocytes, and also caused about 3‐fold of phagocytosis by macrophages within 24 hr after its addition.