Transglutaminase activity in human lymphocytes: early activation by phytomitogens.

Transglutaminase activity is present in human peripheral lymphocytes and is enhanced up to 15-fold within 10-30 min after treatment of the cells with concanavalin A. Phytohemagglutinin has a similar effect. The enzyme is not detected when intact cells are assayed; it is detected only in cell lysates. Concanavalin A enhances transglutaminase activity only when it is incubated with intact cells; concanavalin A treatment of cell lysates has no effect, alpha-Methyl-D-mannoside specifically inhibits the enhancement of transglutaminase activity in cells treated with concanavalin A results from the specific interaction of the lectin with its saccharide binding site on the cell surface, rather than by direct interaction with the enzyme itself. The increased activity of transglutaminase in cells treated with concanavalin A, as compared to unstimulated cells, is maintained under assay conditions in which saturating levels of Ca2+ are present. Transglutaminase may be involved in early cellular events leading to lymphocyte blastogenesis.