Effect of metabolic state on phytohemagglutinin-P agglutination of normal human erythrocytes.

A reproducible quantitative assay for the lectin-mediated agglutination of human erythrocytes, depending on different rates of settling of agglutinated and nonagglutinated erythrocytes, was developed. This assay was used to study the aggregation of human erythrocytes by phytohemagglutinin-P. The aggregation of human erythrocytes by phytohemagglutinin-P was found to depend upon the metabolic state of the cells. Metabolically depleted erythrocytes agglutinated much less readily than did similar cells supplied with adenosine. This was not due to swelling and rigidity of the cells, since erythrocytes in hypotonic solution did not exhibit significantly altered phytohemagglutinin-P agglutination. Metabolically depleted erythrocytes, or erythrocytes from blood stored 8 weeks, lysed and resealed in the presence of ATP, were agglutinated by phytohemagglutinin-P to a much greater extent than control samples without ATP. The presence of Mg2+, either alone or with ATP, had little effect on the agglutinability of the resealed membranes. Low concentrations of Ca2+ (0.2 mM) had little effect on agglutinability, although high Ca2+ (5 mM) inhibited agglutinability of the resealed membranes somewhat. Both metabolically depleted erythrocytes and depleted erythrocytes, previously treated with adenosine, when treated with trypsin released similar amounts of sialic acid. The agglutinability of the trypsinized adenosine-supplemented cells increased more readily than did that of trypsinized metabolically depleted cells. The agglutination of erythrocytes was not affected by cytochalasin B (40 mug/ml). Vinblastine (0.2 mM) caused depleted erythrocytes to agglutinate similarly to adenosine-supplemented erythrocytes, but had no effect on the agglutination of adenosine-supplemented erythrocytes. It is concluded that ATP in the human erythrocyte probably participates in the modulation of phytohemagglutinin-P agglutinability. This is not a consequence of the more rigid membrane known to accompany ATP depletion in the erythrocyte, or of the effect of ATP levels on Ca2+ or Mg2+ content. It appears likely that ATP modulates human erythrocyte phytohemagglutinin-P agglutinability through interaction, direct or indirect, with a membrane-associated component, which might also be sensitivie to vinblastine.     

Glutaraldehyde fixation and the mechanism of erythrocyte agglutination by concanavalin a and soybean agglutinin

To evaluate the importance of lectin receptor mobility and clustering for enhanced cell agglutinability, the effect of glutaraldehyde fixation on the agglutinability of human erythrocytes by concanavalin A and soybean agglutinin was investigated. Agglutinability was evaluated in unperturbed Microtiter^® plates. Fixation increased slightly the agglutinability of the erythrocytes by both lectins. Fixation did not alter trypsin-enhanced agglutinability. Furthermore, when fixed erythrocytes were trypsinized, their agglutinability increased to the level of unfixed, trypsinized erythrocytes.The kinetics of agglutination of fixed and unfixed erythrocytes were monitored in an electronic particle counter. The shear forces associated with the kinetic experiments diminished fixed-cell to fixed-cell agglutination, i.e., both lectins gave slower kinetics of agglutination with fixed erythrocytes than with unfixed erythrocytes. In contrast, the kinetics of concanavalin A-mediated agglutination of trypsinized-fixed erythrocytes mixed with equal numbers of trypsinized-unfixed erythrocytes were indistinguishable from the rapid kinetics of agglutination of trypsinizedunfixed erythrocytes alone. Light microscopy revealed aggregates composed of fixed and unfixed erythrocytes.We conclude that glutaraldehyde fixation does not diminish the agglutinability of human erythrocytes under low-shear conditions. Our results indicate that the enhanced agglutination of trypsinized erythrocytes is not dependent on clustering of lectin receptors. The disruption of agglutination of fixed erythrocytes by shear forces that do not disrupt agglutination of fixed erythrocytes with unfixed erythrocytes suggests that the rigidity of the fixed erythrocyte may prevent stable aggregate formation by fixed erythrocytes alone.     

Effect of metabolic state on agglutination of human erythrocytes by concanavalin

Intact freshly drawn or stored human erythrocytes, which show little agglutination by concanavalin A, become agglutinable by this lectin in the presence of adenosine. α-Methylglucose (10 mM) completely inhibits this agglutination. The concanavalin A agglutination shows no sensitivity to vinblastine or cytochalasin B.Resealed membranes prepared with ATP in lysing and resealing medium give modest agglutinability, while the presence of adenosine in both the lysing and the resealing medium results in a substantial agglutinability of the resealed membranes.Mild trypsin treatment of the erythrocytes causes an enhanced sensitivity to adenosine activation of the concanavalin A agglutination, while extensive trypsin treatment produced highly agglutinable erythrocytes that show no response to the presence of adenosine in the lectin solution. The extensively treated erythrocytes also show concanavalin A agglutination at temperatures below 37°C, under conditions in which intact or moderately treated erythrocytes do not agglutinate, with or without adenosine present.Results suggest that the adenosine activation of concanavalin A agglutination of intact human erythrocytes is mediated through a metabolic conversion of adenosine to a rapidly turned over metabolite which participates directly in the activation of agglutination. The agglutinability does not appear to depend on whole cell ATP levels, but may involve a particular pool of ATP.The effect of variation of cellular metabolic state and the response of particular systems involved in lectin-mediated agglutinability to cellular metabolism seem to be worth consideration in explaining the frequently large differences in agglutinability of und in cells indifferent biological states, such as those encountered in normal and transformed cells.     

Effect of metabolic state on agglutination of human erythrocytes by concanavalin A.

Intact freshly drawn or stored human erythrocytes, which show little agglutination by concanavalin A, become agglutinable by this lectin in the presence of adenosine. alpha-Methylglucose (10 mM) completely inhibits this agglutination. The concanavalin A agglutination shows no sensitivity to vinblastine or cytochalasin B. Resealed membranes preparaed with ATP in lysing and resealing medium give modest agglutinability, while the presence of adenosine in both the lysing and the resealing medium results in a substantial agglutinability of the resealed membranes. Mild trypsin treatment of the erythrocytes causes an enhanced sensitivity to adenosine activation of the concanavalin A agglutination, while extensive trypsin treatment produced highly agglutinable erythrocytes that shown no response to the presence of adenosine in the lectin solution. The extensively treated erythrocytes also show concanavalin A agglutination at temperatures below 37 degrees C, under conditions in which intact or moderately treated erythrocytes do not agglutinate, with or without adenosine present. Results suggest that the adenosine activation of concanavalin A agglutination of intact human erythrocytes is mediated through a metabolic conversion of adenosine to a rapidly turned over metabolite which participates directly in the activation of agglutination. The agglutinability does not appear to depend on whole cell ATP levels, but may involve a particular pool of ATP. The effect of variation of cellular metabolic state and the response of particular systems involved in lectin-mediated agglutinability to cellular metabolism seem to be worth consideration in explaining the frequently large differences in agglutinability of und in cells in different biological states, such as those encountered in normal and transformed cells.     

The effects of neuraminidase on concanavalin a agglutination of erythrocytes: Evidence for adsorption of neuraminidase to erythrocyte membrane

Neuraminidase-treated human erythrocytes, but not untreated erythrocytes, were agglutinated by concanavalin A. The degree of concanavalin A agglutinability was not directly related to sialic acid removal by neuraminidase. While maximal sialic acid release was obtained with 5 units neuraminidase/2 × 10⁹ erythrocytes, maximal concanavalin A agglutination was only obtained after exposure to 20 units neuraminidase. Binding of ³H-concanavalin A by erythrocytes was 10-fold higher with rabbit compared to human red cells.Neuraminidase treatment of human erythrocytes caused a relative increase in ³H-concanavalin binding, but the absolute amount was still 10-fold less than that bound to rabbit erythrocytes. Specific adherence of neuraminidase to Con A-Agarose could not be demonstrated. There was no evidence for contamination of the neuraminidase preparation with proteases using a sensitive assay. These studies suggest that neuraminidase adsorbs to erythrocyte membranes and leads to concanavalin A agglutination of human erythrocytes by a mechanism other than removal of sialic acid.     

Transmembrane Ca2+ gradient is essential for high anion transport activity of human erythrocytes

The role of a transmembrane Ca²⁺ gradient in anion transport by Band 3 of human resealed erythrocyte ghosts has been studied. The results show that a transmembrane Ca²⁺ gradient is essential for the conformation of erythrocyte Band 3 with higher anion transport activity. The dissipation of the transmembrane Ca²⁺ gradient by the ionophore A23187 inhibits the anion transport activity. The extent of this inhibition approaches 90% as the Ca²⁺ concentration on both sides of the ghost membrane is increased to 1.0 mM and half-maximum inhibition is observed at 0.25 mM Ca²⁺. Addition of ATP (0.4 mM) to the resealing medium can partly reestablish the transmembrane Ca²⁺ gradient by activation of Ca²⁺-ATPase and alleviate the inhibition to some extent. N-ethylmaleimide, an inhibitor of erythrocyte Ca²⁺-ATPase, prevents such restoration. Electron micrographs reveal that numerous larger intramembranous particles can be observed on the P-faces of freeze-fractured resealed ghosts in the absence of a transmembrane Ca²⁺ gradient.Abbreviations DPA dipicolinic acid - EITC eosin 5-isothiocyanate - DIDS 4,4-diisothiocyanostilbene-2,2-disulfonate - TES N-Tris-(hydroxymethyl)methyl-2-aminoethane sulfonic acid - PMSF phenylmethyl-sulfonylfluoride - NEM N-ethylamaleimide - BSA bovine serum albumin - EGTA ethyleneglycol-bis (aminoethylether)-tetra-acetic acid - EITC-Band 3 Band 3 labeled with EITC - Ca_i Ca²⁺ inside resealed ghosts - Ca_o Ca²⁺ outside resealed ghosts     

FUSION OF INTACT HUMAN ERYTHROCYTES AND ERYTHROCYTE GHOSTS

Sendai virus is able to induce the fusion of human erythrocytes. Bivalent cations or ATP are not essential for polyerythrocyte formation. High fusion indices were obtained when Sendai virus was added to cells incubated in the presence of both EDTA and iodoacetic acid. Human erythrocyte ghosts prepared by gradual hemolysis still retain the potential to undergo virus-induced fusion. Fusion of human red blood cells without the addition of viruses was obtained by incubation of erythrocytes at pH 10.5 in the presence of Ca⁺⁺ (40 mM) or by addition of phospholipase C Clostridium perfringens preparations to cells previously agglutinated or polylysine.     

Membrane perturbations induced by the interactions of zinc ions with band 3 in human erythrocytes

Of group 12 metals, zinc is an essential element to maintain our life, but other metals such as cadmium and mercury are toxic in cellular activities. Interactions of these metals with biomembranes are important to understand their effects on our living cells. Here, we describe the membrane perturbations induced by these metals in human erythrocytes. Of these metals, Zn²⁺ ions only induced the erythrocyte agglutination. Histidine residues in extracellular domains of band 3 participated in Zn²⁺-induced agglutination. Interestingly, it was found that band 3-cytoskeleton interactions play an important role in Zn²⁺-induced agglutination. In contrast with Hg²⁺ and Cd²⁺ ions, Zn²⁺ ions greatly suppressed pressure-induced hemolysis by cell agglutination. Such a suppression was removed upon dissociation of agglutinated erythrocytes by washing, indicating the reversible interactions of Zn²⁺ ions with erythrocyte membranes. Excimer fluorescence of pyrene indicated that spectrin is denatured by a pressure of 200 MPa irrespective of hemolysis suppression. Taken together, these results suggest that the agglutination of erythrocytes due to the interactions of Zn²⁺ ions with band 3 is stable under pressure, but spectrin, cytoskeletal protein, is denatured by pressure     

Hemagglutination with Gal-N-Ac receptors in the hepatocyte membrane]

By means of mixed agglutination of isolated rat hepatocytes with human group A or rat erythrocytes, both of them were previously trypsinized and sialolyzed, respectively, a hepatocytic N-acetylgalactosamine-receptor was demonstrated. Gal-N-ac specifically inhibits this agglutination. Following oxidation with periodic acid red blood cells no more agglutinate with rat hepatocytes. This agglutination is not related to proteins adsorbed to hepatocytes. The agglutinability of erythrocytes and hepatocytes may bear some relevance to the elimination of old red blood cells.     

Isolation of species-specific and stage-specific adhesion promoting component by disaggregation of intact sea urchin embryo cells

The species-specific and developmental stage-specific aggregation-enhancing supernatant isolated from intact sea urchin (Strongylocentrotus purpuratus) blastula cells incubated in Ca²⁺---Mg²⁺-free sea water is a hemagglutinin. This material agglutinated trypsinized, fixed human type O and B (inhibited by -galactose) erythrocytes, whereas control erythrocytes in Millipore-filtered sea water did not agglutinate. The blastula supernatant agglutinates both live and fixed S. purpuratus blastula cells. Fixed cells were chosen in these experiments so that a standardized, highly reproducible system could be produced by pooling batches of blastula cells. Dissociation supernatant (DS)-mediated agglutination of S. purpuratus blastula cells was blocked by -galactose and N-acetyl- -galactosamine by 10 min of incubation, but not by -glucose, -fucose, -mannose, -glucosamine, -mannosamine or N-acetyl- -mannosamine (all at 0.1 M concentration, the concentration chosen as a result of preliminary experiments). The results were consistently observed in scores of experiments and suggest that DS binds cells together via -galactose-like and N-acetyl- -galactosamine-like residues. We also found that aggregates of live blastula cells formed in the presence of DS gave rise, after 24 h incubation, to viable, swimming embryoids, suggesting that DS-mediated adhesion is physiologically meaningful.     

Different behavior of ghost-linked acidic and neutral sialidases during human erythrocyte ageing

Acidic and neutral sialidases (pH optimum 4.7 and 7.2, respectively) were assayed on human circulating erythrocytes during ageing. The assays were performed on intact erythrocytes and resealed erythrocyte ghost membranes. From young to senescent erythrocytes the acidic sialidase featured a 2.7-fold and 2.5-fold decrease in specific activity when measured on intact cells or resealed ghost membranes, whereas the neutral sialidase a 5-fold and 7-fold increase, respectively.The Ca²⁺-loading procedure was employed to mimic the vesiculation process occurring during erythrocyte ageing. Under these conditions the released vesicles displayed an elevated content of acidic sialidase, almost completely linked through a glycan phosphoinositide (GPI) anchor but no neutral sialidase activity, that was completely retained by remnant erythrocytes together with almost all the starting content of sialoglycoconjugates. The loss with vesiculation of acidic sialidase with a concomitant relative increase of neutral sialidase was more marked in young than senescent erythrocytes.The data presented suggest that during ageing erythrocytes loose acidic sialidase, and get enriched in the neutral enzyme, the vesiculation process, possibly involving GPI-anchors-rich membrane microdomains, being likely responsible for these changes. The enhanced neutral sialidase activity might account for the sialic acid loss occurring during erythrocyte ageing.     

Ethanol-induced alterations in human erythrocyte shape and surface properties: Modulatory role of prostaglandin E1

Summary Exposure of human erythrocytes to ethanol (1 to 20% by vol) in Ca²⁺ and Mg²⁺-free phosphate-buffered saline, pH 7.4, transformed biconcave discs into spiculated echinocytes within 3 min at 25°C. The effects of ethanol were concentration- and time-dependent, but reversible by washing in the incubation buffer system within 60 min of initial exposure to ethanol. After prolonged ethanol exposure (180 min), washing of cells resulted in the formation of stomatocytes (cup-forms). Ethanol-induced echinocytosis was also accompanied by a 30% enhancement in the agglutinability of erythrocytes by ligands with high affinity for negative surface charge (poly-l-lysine and wheat germ agglutinin, 20 l/ml) without any alterations in surface charge topography. Concomitant exposure of erythrocytes to prostaglandin E₁ (100nm) selectively prevented the enhancement of ligand-mediated agglutinability, but did not modify cell shape. These data indicate that certain erythrocyte surface properties may not be directly influenced by cell shape and suggest a unique modulatory action of prostaglandin E₁ on shape-transformed cells.     

Differential lectin-mediated agglutinabilities of the embryonic and the first extraembryonic cell line of the early chick embryo

Summary The lectin-mediated agglutinability of cells dissociated from different areas of the gastrulating chick embryo was investigated. Differences in agglutinability were quantified by using a Coulter counter. Cells from the area pellucida (AP) and those from the endoderm of the area opaca (AOEn) are agglutinated by Concanavalin A (Con A), wheat germ agglutinin (WGA) andRicinus communis agglutinin (RCA). In cells from both areas the greatest agglutination response is obtained with RCA. Trypsinization of AOEn cells enhances their agglutinability with Con A, WGA and RCA. The lectin-induced agglutinability of cells from the area pellucida is similar in EDTA-dissociated and trypsinized cells.Cells from the AP are significantly more agglutinable with Con A than those of the AOEn regardless whether the former are obtained by trypsinization or dissociation with EDTA. The higher agglutinability of cells of the area pellucida with Con A, as well as the differential enhancement by trypsin of the agglutinability of AOEn cells with Con A, WGA, and RCA may reflect a difference in the cell surface glycoreceptors between the cells of the are pellucida (predominantly embryonic) and the first extraembryonic (AOEn) cell line. These cells have been shown to sort out from each other at the earliest stages of development.     

Ca2+ transport activities of inside-out vesicles prepared from density-separated erythrocytes from rat and human

The plasma membrane Ca²⁺ ATPase in erythrocytes is vital for the maintenance of intracellular Ca²⁺ levels. Since the cytoplasmic Ca²⁺ concentration is elevated in older erythrocytes, the properties of the Ca²⁺ transport ATPase were examined during cell aging using inside-out vesicles (IOVs) prepared from density-separated, young (less dense, Ey) and old (more dense, Eo) rat and human erythrocytes. The transport of Ca²⁺ and the coupled hydrolysis of ATP were measured using radiolabeled substrates. The calmodulin-independent Ca²⁺ transport activity (Ey, 38.8 vs. Eo, 23.3 nmols/min/mg IOV protein) and the Ca²⁺ dependent ATP phosphohydrolase activity (Ey, 53.5 vs. Eo, 48.8 nmols/min/mg protein) were greater in IOVs prepared from younger (less dense) rat erythrocytes. The calmodulin-independent Ca²⁺ transport activity in IOVs from human erythrocytes was 12.9 nmols/min/mg IOV protein for Ey and 10.7 nmols/min/mg IOV protein for Eo. Inside-out vesicles from older (more dense) cells exhibited a lower pumping efficiency as determined by the calculated stoichiometry, molecule of Ca²⁺ transported per molecule of ATP hydrolyzed (rat: Ey, 0.74 vs. Eo, 0.49; human: Ey, 1.22 vs. Eo, 0.77). The enzymatic activity of rat and human Ey IOVs was labile. The Ca²⁺ transport activity in Ey but not Eo IOVs rapidly declined during cold storage (4°C). The decrease in Ca²⁺ transport activity during aging may accentuate the age-related decline in several erythrocytic properties.Abbreviations IOV Inside-Out Vesicles - Ey Erythrocytes enriched with young (less dense) cells - Eo Erythrocytes enriched with old (more dense) cells - ACEase Acetylcholinesterase     

Increased Ca2+ -ATPase activity associated with methylation of phospholipids in human erythrocytes.

Ca²⁺-ATPase activity in human erythrocytes is increased by the enzymatic methylation of membrane phospholipids. Erythrocyte membranes incubated in the presence of the methyl donor, S-adenosyl-L-methionine, demonstrate increased Ca²⁺ stimulated ATP hydrolysis, increased [⁴⁵Ca²⁺] efflux from erythrocyte ghosts and synthesis of phosphatidyl-N-monomethylethanolamine. The increase in Ca²⁺-ATPase activity is due to an increase in Vmax, and not due to changes in affinity for ATP or Ca²⁺. The concentration of S-adenosyl-L-methionine needed to stimulate Ca²⁺-ATPase closely matches that needed for the methylation of phosphatidylethanolamine. Both the stimulation of Ca²⁺-ATPase and the methylation of phospholipids are inhibited by the methyltransferase inhibitor, S-adenosyl-L-homocysteine. Membrane fluidity is increased by phospholipid methylation, which may be the mechanism for Ca²⁺-ATPase stimulation.     

Receptor distribution and the mechanism of enhanced erythrocyte agglutination by soybean agglutinin

We have examined the role of receptor clustering in intact erythrocyte membranes exhibiting enhanced lectin-mediated cell agglutination by analyzing freeze-fracture and freeze-etch images of human erythrocytes labeled with ferritin-conjugated soybean agglutinin. We find that trypsinization and fixation of intact erythrocytes, in either order, causes no alteration of the random distribution of ferritin-conjugated soybean agglutinin on the surfaces of these cells as compared to their distribution on the surfaces of fixed erythrocytes and untreated erythrocyte ghosts. Furthermore, clustering of the intramembranous particles in the membrane of intact erythrocytes was not found with any of the cells described above.We conclude that clustering of the soybean agglutinin receptors is not a major factor involved in the enhanced agglutination of intact trypsinized erythrocytes. Caution is necessary in transferring information obtained with erythrocyte ghosts, where clustering can be induced, to intact erythrocytes.     

The mechanism of vanadium action on selective K+-permeability in human erythrocytes

Low concentrations of chelating agents such as EDTA prevent the air oxidation of vanadyl (VO²⁺, +4 oxidation state) to vanadate (VO₃^?, +5 oxidation state). Under these conditions, the ionophore A23187 mediates the rapid entry of vanadyl into human erythrocytes. In the presence of A23187, vanadyl at concentrations in excess of EDTA gives rise to a dramatic increase in K⁺ permeability, which is very similar to the Gardos Ca²⁺-induced K⁺ permeability increase with respect to ion selectivity, response to inhibitors, effects of pH, and stimulation by external K⁺. In ultrapure media with very low Ca²⁺, however, vanadyl has no effect on K⁺ permeability. These experiments suggest that Ca²⁺ is displaced from EDTA by vanadyl and then enters the cell via A23187 where it triggers the increase in K⁺ permeability. This hypothesis is confirmed by experiments demonstrating that vanadyl does displace Ca²⁺ from EDTA. Vanadate, an inhibitor of Ca²⁺-ATPase, causes a selective increase in K⁺ permeability in metabolically depleted cells, but the increase is abolished by low concentrations of EDTA, indicating that this effect is also due to entry of extracellular Ca²⁺. Earlier observations of effects of vanadyl and vanadate on erythrocyte K⁺ permeability can thus be explained on the basis of inhibition of the Ca²⁺ pump by vanadium, leading to an increase in intracellular Ca²⁺ concentration.     

Effect of antihistamines and chlorpromazine on the calcium-induced hyperpolarization of the Amphiuma red cell membrane

1. 1. It has previously been demonstrated that an increase in extracellular Ca²⁺ concentration induces a transient increase in K⁺ permeability and associated hyperpolarization of the red cell membrane of the giant salamander, Amphiuma means. This phenomenon is analogous to the Ca²⁺-induced KCl loss observed in ATP-depleted human red cells and red cell ghosts.

2. 2. Histamine, which enhances the Ca²⁺-induced K⁺ loss from depleted human red cells, is without effect on this Ca²⁺-induced hyperpolarization of Amphiuma red cells.

3. 3. Promethazine (10 μM) and mepyramine (1 mM), which inhibit the Ca²⁺-induced K⁺ loss in depleted human red cells, also block the Ca²⁺-related hyperpolarization of Amphiuma erythrocytes.

4. 4. Chlorpromazine (25 μM), despite being a weak antihistamine, is equally effective in blocking the Ca²⁺-induced hyperpolarization of Amphiuma red cells.

5. 5. Ionophore A23187 causes a large and sustained Ca²⁺/K⁺-dependent hyperpolarization even in the presence of normal (1.8 mM) concentrations of Ca²⁺. This hyperpolarization is relatively insensitive to chlorpromazine and promethazine.

6. 6. The inhibition of the Ca²⁺-induced hyperpolarization of the Amphiuma red cell membrane by chlorpromazine and promethazine may be related to their properties as local anaesthetics.

Purification and Characterization of Two Lectins from the Sea Cucumber Stichopus japonicus

Two Ca^{2 +}–dependent lectins were purified from the sea cucumber Stichopus japonicus by affinity chromatography on lactosyl-Sepharose 4B and ion-exchange chromatography on Q-Sepharose. Their molecular masses were estimated to be 13kDa (SJL-I) and 15kDa (SJL-II) on SDS-PAGE. SJL-I agglutinated rabbit erythrocytes as well as human A, B, and O-type erythrocytes, but SJL-II agglutinated only rabbit erythrocytes. Hemagglutination by SJL-I was competitively inhibited by N-acetyl-D- galactosamine and galactose-containing carbohydrates. On the other hand, only lactose, melibiose, and raffinose gave weak inhibition of hemagglutination by SJL-II, suggesting that SJL-II may have high specificity for particular complex carbohydrate(s) on the surface of rabbit erythrocytes. SJL-II was activated at ten times lower Ca²⁺ concentration than SJL-I. Both lectins lost activity in acidic pH, while SJL-I appeared more stable down to pH 4.5.