Inhibition of lymphocyte 5′-nucleotidase by lectins: effects of lectin specificityand cross-linking ability

Abstract

5'-Nucleotidase, an integral glycoprotein enzyme of the lymphocyte plasma membrane, is inhibited cooperatively by the lectin concanavalin A. Because divalent succinyl-concanavalin A is a poor enzyme inhibitor, both binding and lectin-induced cross-linking of 5'-nucleotidase may be necessary for inhibition. Succinyl-concanavalin A does not compete with concanavalin A for binding to the enzyme; however, maleyl-concanavalin A, another poor inhibitor, competes effectively with the parent lectin. Thus, maleyl-concanavalin A binds to the same site as concanavalin A but causes little inhibition, whereas succinyl-concanavalin A does not bind to this site. The monovalent lectin from Ricinus communis (RCA-60) is a more effective enzyme inhibitor than the related divalent lectin (RCA-120), and inactivation of the second low-affinity sugar binding site on RCA-60 does not abolish inhibition, suggesting that multivalent cross-linking is not required for 5'-nucleotidase inhibition. Peanut and wheat germ agglutinins do not inhibit the enzyme, whereas lectins from lentil, pea, soybean, Griffonia simplicifolia, and Phaseolus vulgaris inhibit 5'-nucleotidase with various degrees of effectiveness. The only lectin showing strong positive cooperativity in its interaction with 5'-nucleotidase is concanavalin A.

Release of the glycosylphosphatidylinositol-anchored enzyme ecto-5′-nucleotidase by phospholipase C: catalytic activation and modulation by the lipid bilayer

“…5h-NTase plays an important role in purine salvage in lymphocytes, where it is known as CD73, and has also been implicated in transmembrane signalling in itro in T-lymphocytes [12]. The enzyme is N-glycosylated, and binding of a variety of lectins to N-linked carbohydrates on 5h-NTase is known to inhibit activity [15,16], suggesting that some communication exists between the glycan chain(s) and the catalytic site.…”

Identification of inactive ecto‐5′‐nucleotidase in normal mouse muscle and its increased activity in dystrophic Lama2dy mice

“…Because the enzyme is inhibited by several lectins (Sharom et al, 1988), a last attempt to find possible differences in the kinetic properties of eNT of NM and DM was made. Assays with increasing Con A concentrations (0.048 -1.92 M) showed that the lectin decreased eNT activity by up to 52%.…”