Inhibition of lymphocyte 5'-nucleotidase by lectins: effects of lectin specificity and cross-linking ability.
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.
Sharom
F J
FJ
Department of Chemistry and Biochemistry, University of Guelph, Ont., Canada.
Lamb
M P
MP
Kupsh
C C
CC
Head
S
S
D015720:5'-Nucleotidase; D002462:Cell Membrane / Q000201:enzymology; D003208:Concanavalin A / Q000494:pharmacology; D003432:Cross-Linking Reagents; D006801:Humans; D037102:Lectins / Q000494:pharmacology*; D008214:Lymphocytes / Q000201:enzymology*; D009708:Nucleotidases / Q000037:antagonists & inhibitors*; D037121:Plant Lectins; D010947:Plants, Toxic; D012278:Ricinus; D013379:Substrate Specificity
D003432:Cross-Linking Reagents; D037102:Lectins; D037121:Plant Lectins; D003208:Concanavalin A; D009708:Nucleotidases; D015720:5'-Nucleotidase