Proteolytic activity associated with human erythrocyte membranes. Self-digestion of isolated human erythrocyte membranes

Membrane-bound high molecular mass proteinases from human erythrocytes

Two high molecular mass proteinases, multicatalytic proteinase (MCP) and a new high molecular mass proteinase (HMP) with only chymotrypsin-like activity (Khan et al. (1994) J. Biol. Chem. 269, 10016-10021) from human erythrocyte membranes, have been compared. For this purpose, MCP was purified from human erythrocyte membranes in the active form towards synthetic peptide substrates; it also hydrolysed the protein substrates [14]methyl casein and [14C]oxidised insulin beta chain at 37 degrees C. MCP from plasma membranes exhibited hollow cylindrical structures also typical of cytosolic forms. Radiolabelled diisopropyl fluorophosphate, [3H]DFP, a serine proteinase inhibitor, labelled a band of Mr 23 000 in membrane MCP. By contrast, no labelling was obtained with HMP. Chymotrypsin-like activity of HMP was also found to be insensitive to DFP. On the other hand, DFP inhibited chymotrypsin-like and peptidylglutamyl peptide hydrolysing activities of membrane MCP, with no effect on its trypsin-like activity. The inhibition of MCP by DFP was concentration-dependent. These studies showed that MCP and HMP represent two distinct kinds of proteinases with chymotrypsin-like activities and can be distinguished by the serine proteinase inhibitor DFP.

Evidence for the formation of endothelin by lysed red blood cells from endogenous precursor

The release of endothelin from various blood cell fractions was investigated. Human as well as rat blood cell fractions homogenized by sonification were incubated in buffer for up to 60 min. Neither in platelet nor leukocyte homogenates from either species could immunoreactive endothelin be detected. In contrast, homogenates of red blood cells from both species showed a rapid and time-dependent rise of immunoreactive endothelin levels, reaching a peak at 15 min and decreasing thereafter. However, at time point 0 no immunoreactive endothelin could be detected. Reverse phase high performance liquid chromatography showed immunoreactive endothelin to consist of endothelin-1 as well as big endothelin-1. The release of immunoreactive endothelin in human and rat homogenates was concentration-dependently inhibited by the protease inhibitors, leupeptin, phosphoramidon, chymostatin and pepstatin A in order of increasing potency. Intact red blood cells did not incorporate [125I]endothelin-1 nor did they transform exogenous big endothelin-1 to endothelin-1. However, haemolysis of red blood cells with hypotonic saline (0.2%) or incubation with pore-forming staphylococcal alpha-toxin induced the release of immunoreactive endothelin into the buffer samples. Thus, apart from the indirect vasoconstrictor, haemoglobin, red blood cells can also liberate the direct vasoconstrictor, endothelin, a finding expected to be of considerable pathophysiological significance.

Haemagglutinating and haemolytic activity of the extracellular vesicles of Bacteroides gingivalis W50

The extracellular vesicles (ECV) and extracellular protein (EP) fractions of Bacteroides gingivalis W50 showed haemagglutinating (HA) activity towards sheep erythrocytes. Similar fractions from the nonpathogenic strain W50/BE1 did not haemagglutinate. W50 ECV HA activity was not inhibited by various glycosidase, phospholipase or protease pretreatments, sugars or amino acids, including arginine or lysine. The haemagglutinating activity of ECV was associated only with the extracellular vesicle membrane. The EP and ECV of both strains displayed haemolytic activity. This activity was apparently depressed in the presence of 10 mM dithiothreitol (DTT). All EP and ECV fractions degraded certain structural sheep erythrocyte membrane proteins. The greatest activity was displayed by W50 ECV and W50/BE1 EP and was enhanced by DTT. In the presence of DTT, the ECV of both strains degraded purified human haemoglobin but this activity was greatly reduced in its absence.

Changes in the proteolytic activity of human erythrocyte membrane during red cell aging

The action of endogenous membrane proteinases in membranes isolated from human red cells of various ages was assayed by three groups of methods: (1) determination of the amount of protein fragments released to the acid-soluble fraction; (2) monitoring of changes in ESR spectra of maleimide spin-labeled erythrocyte membranes; (3) electrophoretic methods: a two-dimensional analysis and analysis of the activity inside SDS-PAGE gels. For all the methods the effects of proteinase action were highest in ghosts isolated from the erythrocytes of middle age.

Proteolysis of N-ethylmaleimide-modified aldolase loaded into erythrocyte ghosts: prevention by inhibitors of calpain

1. When rabbit muscle aldolase labelled with tritium and inactivated by N-ethylmaleimide (NEM) was loaded into erythrocyte ghosts, significant proteolysis of the loaded protein occurred. The major product of this proteolysis, separated by electrophoresis under dissociating conditions, was found to be approx. 2 kDa smaller than the parent protein. 2. Proteolysis was detectable during erythrocyte ghost loading at 0 degrees C, reaching a plateau after approx. 12 min. Subsequent incubation at 37 degrees C to allow resealing of the ghosts resulted in additional proteolysis, and up to 20% of the loaded protein was converted to the smaller 38 kDa derivative. 3. EDTA, EGTA, leupeptin and chymostatin, each inhibitors of calcium-activated neutral proteinases (calpains), were the most effective inhibitors of the proteolysis of NEM-inactivated aldolase in ghosts. Other proteinase inhibitors were ineffective, while phenylmethanesulphonyl fluoride was only partially effective. 4. Inhibition of the proteolysis by EGTA was prevented by CaCl2, supporting the involvement of erythrocyte calpain. 5. Pretreatment of ghosts with EGTA prior to loading of NEM-modified aldolase followed by microinjection of the protein into HeLa cells did not result in a different rate of its overall breakdown to acid-soluble products. EGTA is suggested as a useful agent for the erythrocyte ghost-mediated microinjection of calpain-sensitive proteins.

Proteolytic activity of human erythrocyte membrane during ghosts preparation

1. Proteins in human erythrocyte membranes after red blood cells hemolysis revealed relatively high rate of self-digestion. 2. This indicates hemolysis as a critical moment for membrane proteases activation. 3. The detailed pattern of band 3 protein and spectrin degradation during ghosts preparation was more complicated and reflected both the changes in proteolytic susceptibility and extraction of some proteases. 4. Further extraction of membrane proteins by alkali stripping resulted in an increase in the self-digestion rate and decrease in the degradation rate of an exogenous substrate.

Further studies on rat cathepsin E: subcellular localization and existence of the active subunit form

The subcellular localization of rat neutrophil cathepsin E was examined by a modification of the method of N. Borregaard et al. [(1983) J. Cell Biol. 97, 52-61]. When the postnuclear cavitate of rat neutrophils was subjected to density centrifugation on discontinuous Percoll gradients, three particulate bands, P1 (lowest; azurophil granule rich), P2 (middle; specific granule rich), and P3 (highest; plasma membrane rich), were segregated. A combined application of immunochemical and electrophoretic methods revealed a striking difference in subcellular localization between cathepsin E and cathepsin D: Cathepsin E was associated with P3 and soluble fractions, and cathepsin D was chiefly associated with P1 and P2 fractions. The results thus indicate that cathepsin E is a nonlysosomal acid proteinase in rat neutrophils. It was found that cathepsin E existed in two enzymatically active molecular forms, referred to as CE-I and CE-II, in rat neutrophil extracts. To examine the relationships between the two forms, cathepsin E was purified to homogeneity from rat gastric mucosae. The purified enzyme exhibited a single protein band of 43 kDa on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, but electrophoresis without SDS, followed by visualization of activity in the gel, revealed two activity bands corresponding to CE-II and CE-I in neutrophil extracts. Pretreatment of the enzyme with beta-mercaptoethanol or dithiothreitol resulted in an increase in CE-I activity with a concomitant decrease in CE-II activity on gels. Upon gel filtration, the molecular weights of CE-II and CE-I were estimated to be 98,000 and 51,000, respectively, strongly suggesting that they are the dimeric and monomeric forms of the cathepsin E subunit.

Degradation of native and modified forms of fructose-bisphosphate aldolase microinjected into HeLa cells

The uptake and degradation of radiolabelled rabbit muscle fructose-bisphosphate aldolase (EC 4.1.2.13) was studied in HeLa cells microinjected by the erythrocyte ghost fusion system. Labelled aldolase was progressively modified by treatment with GSSG or N-ethylmaleimide (NEM) before microinjection to determine whether these agents, which inactivate and destabilize the enzyme in vitro, affect the half-life of the enzyme in vivo. Increasing exposure of aldolase to GSSG or NEM before microinjection increased the extent of aldolase transfer into the HeLa cells and decreased the proportion of the protein that could be extracted from the cells after water lysis. Some degradation of the GSSG- and NEM-inactivated aldolases was observed in the ghosts before microinjection; thus a family of radiolabelled proteins was microinjected in these experiments. In spite of the above differences, the 40 kDa subunit of each aldolase form was degraded with a half-life of 30 h in the HeLa cells. In contrast, the progressively modified forms of aldolase were increasingly susceptible to proteolytic action in vitro by chymotrypsin or by cathepsin B and in ghosts. These studies indicate that the rate of aldolase degradation in cells is not determined by attack by cellular proteinases that recognize vulnerable protein substrates; the results are most easily explained by a random autophagic process involving the lysosomal system.

Characterization of an intracellular insulin-degrading enzyme in human erythrocytes

Using conventional techniques of ammonium sulfate fractionation and Sephadex gel column chromatography, insulin-degrading enzyme was partially purified from lysate of human erythrocytes. The enzymatic activity was measured by the trichloroacetic acid precipitation method. Compared to trypsin, the enzyme was highly specific for insulin. The apparent molecular weight of the enzyme was 160,000 Da, the optimum pH was the 7.4 to 7.8 range, and the Km value for insulin for the partially purified enzyme was 162 nM. Bacitracin and N-ethylmaleimide were potent inhibitors, while chloroquine, ethylenediaminetetraacetate, antipain, and soybean trypsin inhibitor failed to inhibit the activity of the enzyme. Like most nucleated cells, human erythrocytes not only have the membranal insulin receptors, but also possess the cytosolic specific insulin-degrading enzyme. Insulin internalization and degradation are shown to be due to the receptor and the enzyme acting in concert as in many nucleated cells. Anucleated erythrocytes have both these entities for possible internalization and degradation of insulin.

Proteolytic activity in electropherograms (SDS-PAGE) of bovine erythrocyte ghosts

1. Activity of proteases, strongly related with erythrocyte membrane, was analysed employing a new methodological approach. 2. Intact bovine ghosts, ghosts depleted in peripheric proteins or purified Triton X-100 and ghost extracts were electrophoresed and the proteolytic activity in the gel fragments (SDS-PAGE) was assayed. 3. At least two proteases that were inhibited by EDTA and PMSF were found.

Cathepsin E from rat neutrophils: its properties and possible relations to cathepsin D-like and cathepsin E-like acid proteinases

An extract of rat neutrophils was found to contain a high hemoglobin-hydrolyzing activity at pH 3.2, about 70% of which does not cross-react with anti-rat liver cathepsin D antibody. A neutrophil non-cathepsin D acid proteinase was successfully isolated from cathepsin D and characterized in comparison with the properties of rat liver cathepsin D. The neutrophil enzyme differed from cathepsin D in chromatographic and electrophoretic behaviors as well as immunological cross-reactivity, and its molecular weight was estimated to be 98,000 by gel filtration on Toyopearl HW 55. These findings strongly suggest that the neutrophil enzyme could be classified as cathepsin E. The enzyme, now designated rat cathepsin E, had an optimal pH at 3.0-3.2, preferred hemoglobin to albumin as substrate, and was markedly resistant to urea denaturation. Rat cathepsins D and E cleaved the insulin B-chain at six and eight sites, respectively; five sites were common for both enzymes. Possible relations among cathepsin E and cathepsin D-like or E-like acid proteinases reported so far were discussed.

Modification of L-triiodothyronine binding sites from rat erythrocyte membrane by heating and by proteinase treatments

The number of binding sites for L-triiodothyronine in rat erythrocyte membranes was increased 2-fold by incubation at 37 degrees C for 60 min. An increase of approximately 3-fold was found when the incubation was carried out at 50 degrees C. The proteinase inhibitor phenylmethylsulfonyl fluoride abolished the effect. Similar increments in the number of binding sites were obtained by treatment of the membranes with proteinases. The Kd values (0.09 X 10(-10) M and 3.6 X 10(-10) M for the high-affinity and the low-affinity binding sites, respectively) remained unchanged after the treatment, as did the free-SH group requirements, storage stability and stereospecificity. Our results suggest that endogenous proteolytic activity could be involved in the increase of the number of membrane latent sites for L-triiodothyronine.

Species differences in the expression of caseinolytic proteinases and plasminogen activators by bone marrow cells

Intact viable bone marrow cells from hamsters (Mesocricetus aruatus), rat (Rattus norvegicus), guinea pig (Cavia porcella) and rabbit (Oryctolagus cuniculus) were analyzed for caseinolytic proteinases and plasminogen activator activity. Species specific quantitative and qualitative differences in caseinolytic activity were detected. Quantitative and qualitative differences in plasminogen activator expression were observed. Cellular fractionation experiments revealed a heterogenous distribution of plasminogen activator activity among subpopulations of cells. The plasminogen activator activity associated with bone marrow cells behaved as ectoenzymes. These results indicated that different species may regulate bone marrow cell proteinase activity in a species-specific manner, compatible with their unique regulatory requirements.

Red blood cell-mediated microinjection: methodological considerations

Red blood cell-mediated microinjection is a powerful approach to introducing proteins into the cytoplasm of cultured cells. In the course of our microinjection studies of intracellular protein degradation, we have encountered several potential problems with certain proteins. The microinjection procedure may be accompanied by denaturation of protein by radiolabeling procedures, binding of protein to red cell ghosts during loading, degradation of protein by the red cell ghost prior to microinjection, and adsorption of protein that leaks from red cell ghosts in the presence of fusogen to the fibroblast monolayer. We conclude with a list of points that must be considered prior to use of red cell-mediated microinjection to study a particular protein.

Isolation of a protein labeled with diisopropyl fluorophosphate on stimulation of polymorphonuclear leukocytes with immune complexes

As demonstrated by others, diisopropyl fluorophosphate (DFP) markedly inhibits the O2- generation from guinea-pig polymorphonuclear leukocytes (PMN) stimulated by an antibody complex with ovalbumin (Ag-Ab complex), and also the intracellular uptake of antibody-sensitized erythrocytes by the cells. However, when PMN were treated with DFP and washed to remove the inhibitor, they again became able to exhibit the O2- -generating and phagocytic activities. The [3H]DFP-labeling of intact PMN followed by solubilization with Triton N101, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the existence of several [3H]DFP-labeled proteins with different mol. wts, which disappeared on pretreatment of cells with cold DFP. However, stimulation of DFP-pretreated PMN with Ag-Ab complex in the presence of [3H]DFP resulted in the appearance of a [3H]DFP-labeled, membrane-bound protein with a mol. wt of 40,000. This protein was isolated by affinity chromatography of the solubilized PMN and phagosomes on anti-Ig antibody-Sepharose 4B. Although the enzymatic properties of the protein are not clear, the results so far obtained suggest that it is a putative, stimulus-activated serine protease participating in the triggering events leading to the activation of NADPH oxidase responsible for the respiratory burst and the formation of phagosomes.

Proteolysis-associated deglycosylation of beta 1-adrenergic receptor in turkey erythrocytes and membranes

A protease that can be inhibited by glutathione, dithiothreitol, and o-phenanthroline but not by ethylenediaminetetraacetic acid converts the 50-kilodalton beta-adrenergic receptor in turkey erythrocyte membranes to a 40-kDa polypeptide which retains the specific ligand binding site. This conversion is attenuated in intact erythrocytes. The large 50-kDa peptide contains N-linked, complex carbohydrates and is retained on wheat germ agglutinin-Sepharose. The 40-kDa product of proteolysis does not bind to the wheat germ agglutinin and can thus be separated from the 50-kDa polypeptide by lectin chromatography. However, the large difference in molecular weights of the two receptor peptides cannot be accounted for solely by the different extent of glycosylation.

Erythrocyte membrane abnormalities in patients with amyotrophic chorea with acanthocythosis. Part 2. Abnormal degradation of membrane proteins

Bands 2.1, 3 and 4.2 of the erythrocyte membrane proteins in chorea-acanthocytosis are self-digested faster than those in normal controls. The junction between spectrin and band 3 protein at the cytoplasmic side of the patients' erythrocyte membranes may have some conformational defects. The conformational defects of the proteins may be responsible for the low fluidity in the interior of the patients' erythrocyte membranes. These basic molecular defects may be widespread in other extraneural cell membranes as well as in neuronal cell membranes.

Proteolytic self-digestion of bovine erythrocyte membranes

"Self-digestion" of bovine erythrocyte membrane proteins was studied in isolated membrane preparations during prolonged incubation at 37 C. Protease activities associated with the membrane result in progressive degradation of all main erythrocyte membrane proteins, in particular spectrin and Band 3, and formation of lower molecular weight products which have been tentatively assigned to parent molecules. Membrane protein "self-digestion" occurs in a broad pH range (2-11), is inhibited by increased ionic strength and by inhibitors of metalloproteases, cysteine and serine proteases, and activated by low concentrations of SDS. "Self-digestion" also takes place in NaOH-stripped erythrocyte membranes. The activity of a protease involved in the "self-digestion", of apparent molecular weight of about 35,000, was renatured after SDS-polyacrylamide gel electrophoresis of erythrocyte membrane proteins.

Solubilization, reconstitution, and attempted affinity chromatography of the sugar transporter of the erythrocyte membrane

Reconstitution of the sugar transport system of human erythrocytes into artificial liposomes was achieved by freezing, thawing, and sonicating preformed phospholipid vesicles in the presence of intact ghosts, protein-depleted ghosts, or detergent-treated ghosts. D-glucose equilibrium exchange activities and affinity constants in the range of the reported erythrocyte values were reached in the best experiments. Whereas the extraction of peripheral membrane proteins did not depress the transport function crucially after reconstituting these protein-depleted ghosts, the selective solubilization of integral membrane proteins by a variety of nonionic detergents resulted in an uncontrollable, continuously increasing inactivation of the carrier. However, Emulphogene BC-720 extracts could be prepared in which the glucose transporter retained activity for days at 4 degrees C. These extracts were applied to affinity chromatography matrices of phloretin-Agarose, prepared by coupling phloretinyl-3'-benzylamine (PBA) to CH-Sepharose 4B and to Affigel 202. Although the solubilized sugar transporter appeared to be selectively adsorbed to both PBA matrices, it could not be eluted by specific counter ligands or gentle eluants in a biologically active form. However, chaotropic agents could be used to elute intrinsic proteins, including bands 3 and 4.5, from the Affigel affinity medium.

Insulin degradation in human erythrocyte: effects of cations

Insulin degradation by human erythrocyte fractions was studied using the TCA-precipitation method. Hemolysate exhibited an insulin degrading activity higher than membranes. Triton X-100 treatment of membranes led to the appraisal of Triton-soluble degrading activity and of a more efficient Triton-not-soluble degrading activity. Monovalent cations (Na+, K+, Li+) did not modify the insulin degradation by any of the erythrocyte fractions. Divalent cations, Ca++ and Zn++ selectively enhanced insulin degradation by the membranous fractions, and Cu++ and Zn++ strongly inhibited insulin degradation by all the erythrocyte fractions. The results supported the hypothesis of the existence of at least two different degrading systems in human erythrocytes: soluble (cytosolic) Ca++ and Mg++ insensitive system(s) and membrane associated Ca++ and Mg++ sensitive system(s).

Identification of a kallikrein-like latent serine protease in human erythrocyte membranes

We have discovered and characterized a kallikrein-like latent serine protease in intact human erythrocytes and ghosts. The enzyme is activatable by trypsin. The solubilized enzyme has esterolytic activity with a pH optimum of 9; but the membrane-associated activity increases almost linearly up to pH 10. The activated enzyme releases kinin from bovine low molecular weight kininogen. Enzyme activity is inhibited by TosLysCH2Cl , phenylmethylsulfonyl fluoride, aprotinin and amiloride, and weakly by soybean or lima bean trypsin inhibitor. It is inhibited by Co2+, Zn2+ and Mn2+ but is stimulated by Fe2+, deoxycholate and phospholipase A2. An erythrocyte membrane protein (Mr = 88,000) with an active site serine residue was identified with [14C]-diisopropylphosphorofluoridate labeling. Consistent with the finding of tryptic activation of the latent erythrocyte serine protease, trypsin treatment reduced the density of labeling of this protein and revealed a lower molecular weight form (Mr = 64,000). Possible relationships between the activity of this newly identified serine protease and events such as erythrocyte membrane ion fluxes might be of interest.

Insulin degradation in human erythrocytes. Effect of triton X-100 treatment on insulin-degrading activity of membranes

Human erythrocyte membrane has been demonstrate to possess an insulin-degrading activity. This activity is not due to a contamination by cytosolic factors and seems to be specific toward insulin. The fractionation of the erythrocyte membrane by Triton X-100 leads to the appraisal of an insulin-degrading activity in the Triton-extracted membranes higher than that present in the solubilized protein fraction. The degrading activity found in the extracted membranes is inhibited by the addition of the solubilized material. This last fraction seems to modulate, in the intact membrane, the whole insulin-degrading system.

Membrane-mobility agent-promoted fusion of erythrocytes: fusibility is correlated with attack by calcium-activated cytoplasmic proteases on membrane proteins

Rat, but not human, erythrocytes undergo fusion promoted by the membrane-mobility agent 2-(2-methoxyethoxy)-ethyl cis-8-(2-octylcyclopropyl)octanoate (A2C). The difference in behavior is correlated with rat erythrocyte membrane protein degradation caused by Ca2+-activated proteases. The human erythrocyte is deficient in such protease activity. Membrane protein degradation is a necessary, but not sufficient, requirement for membrane fusion. Membrane protein degradation probably releases membrane components from certain constraints. In addition, the motion of membrane components precedes fusion and must be promoted by reagents such as A2C, leading to the creation of fusion-potent lipid areas. This sequence of chemical and physical events occurs in other fusion processes.

Reconstitution of glucose transport using human erythrocyte band 3

Band 3 and the diffuse component of zone 4.5, designated band 4.5.B, have been separately prepared from human erythrocyte membranes and incorporated into the membranes of 150 nm 1-palmitoyl-2-oleoyl phosphatidylcholine vesicles. The rates of glucose influx into these vesicles were measured under zero-trans conditions. Both sets of vesicles exhibited substrate-saturable transport which was inhibited by phloretin. However, the specific activity of the band 3 vesicles, 292 mumol X min-1 X (mg protein)-1, was more than twice that of the band 4.5.B vesicles, and the turnover number of transporters in the band 3 vesicles was at least 4-fold greater than those in the 4.5.B vesicles. Very little background density was visible in the band 4.5 region of erythrocyte membranes protected from degradation. In unprotected membranes, band 4.5.B was abundantly present, could be purified, and had glucose transport activity. Previously we have shown (Biochemistry 19, 1205 (1980] that maltosyl isothiocyanate, an affinity label for the glucose transporter, labelled a single 100 000 Mr protein of the intact erythrocyte membrane. Based upon the results of both affinity labelling and reconstitution we suggest that the native glucose transporter is a component of band 3, and that band 4.5.B contains a partially active fragment of the native transporter.

Optimized procedures for investigating changes in human erythrocyte membrane proteins using treatment with calcium and various proteases

In order to establish reproducible sensitive techniques for investigating diseases in which membrane defects have been implicated, human red cell membrane proteins were studied by SDS electrophoresis in ghosts prepared from the blood of 35 separate adult donors using treatment with 1 mmol/l calcium and proteolytic dissection under standardized conditions. The effects of calcium were consistent with increased binding of cytosolic proteins in membranes from fresh blood and endogenous proteolysis in membranes from aged blood. Exogenous proteolysis was most effective with trypsin and was facilitated both by pre-binding this protease to the membrane and by inclusion of 1 mmol/l Ca2+. The nature and extent of these effects was highly dependent on the storage time of the blood. Preliminary indications of cleavage fragment length polymorphism was obtained after treatment with the S. aureus V8 protease but not after trypsin or alpha chymotrypsin treatment.

Proton NMR spectroscopic studies of dipeptidase in human erythrocytes

In studies on human erythrocyte metabolism in situ, high resolution (400 MHz) 1H spin-echo NMR spectroscopy was used to follow the time dependence of hydrolysis of glycylglycine and L-cysteinylglycine in intact cells and their lysates. The concentration dependence of the hydrolysis of L-cysteinylglycine was described by a rectangular hyperbola with Km, 3.5 +/- 0.6 mmol/l lysate and Vmax, 64.2 +/- 3.2 mmol/l lysate/h. We demonstrated that glycylglycine readily enters the erythrocyte and we introduce a means of analysing the data from the coupled reaction sequence; the sequence consists of transport followed by enzyme catalysed hydrolysis.

Studies of factors regulating the ageing of human erythrocytes--V. The role of vesiculation in the loss of membrane-bound sialic acid

1. Erythrocytes aged in vitro in protein-free media with and without leukocytes, release glycopeptides and vesicles. 2. Addition of soybean trypsin inhibitor (SbTI) blocks almost completely the release of glycopeptides but not the vesiculation. 3. Vesicles appear as a heterogeneous population with a diameter of 125 +/- 20 nm and with a lower content of N-acetylneuraminic acid (NAN) than ghosts of the original erythrocytes. 4. The NAN:phosphorus and NAN:cholesterol ratios in the vesicles are lower than in intact membranes. 5. The results indicate a redistribution of membrane components during in vitro erythrocyte incubation and the major importance of sialopeptides release in comparison with vesiculation.

Isolation and partial characterization of the sialoglycoprotein fraction of murine erythrocyte ghosts

With the lithium diiodosalicylate (LIS1) extraction-phenol partition method, we have isolated a sialoglycoprotein fraction from DBA/2 mouse erythrocyte ghosts. We have demonstrated that the Laemmeli system for SDS PAGE can resolve this fraction into four monomers of which two (gp-2.1 and gp-3.1) appear to be authentic, whereas the other two (gp-2.2 and gp-3.2) are probably generated from gp-2.1 and gp-3.1, by limited proteolysis during the isolation procedure. All four components contain O-acetylated neuraminic acid residues, can be stained with Periodic acid-Schiff reagent (PAS) and with Coomassie Brilliant Blue (CB), and can be radioiodinated with the lactoperoxidase-glucose oxidase (LPO-GO) method. All monomers but especially gp-2.1 and gp-3.1 generate characteristic aggregates during solubilization in SDS. The aggregation is enhanced by boiling at high concentrations, and can be reversed by boiling at low concentrations. In addition, the fraction contains a diffuse component present also in ghosts which stains poorly with CB and with PAS and cannot be radioiodinated by the LPO-GO technique. SDS PAGE in the Steck and Yu gel system does not give an accurate separation of the sialoglycoprotein monomers.

Neutral proteinases from human blood cells

1. Human erythrocytes essentially essentially uncontaminated by leukocytes retain considerable proteolytic activity in the membrane fraction. 2. The enzyme responsible has similar properties to previously-reported human erythrocyte membrane proteinases. 3. A particulate fraction from human leukocytes does not yield a similar enzyme when extracted and fractionated in the same way.

Degradation of band-3 glycoprotein in vitro by a protease isolated from human erythrocyte membrane

The use of soybean-trypsin-inhibitor-Sepharose-4B to purify a protease present in human erythrocyte membranes is described. The fraction bound in the presence of calcium to the affinity absorbent is active on band-3 glycoprotein in a non-ionic detergent solution at neutral pH. Band-3 glycoprotein is degraded into components having the mobilities of the proteins of bands 4.5, 7 and of lower molecular weights. When calcium is omitted from the membrane extract, an inactive form of this enzyme can be purified. By DEAE-cellulose chromatography this inactive form can be converted into the active form, presumably by dissociation of an enzyme-inhibitor complex.

A high molecular weight peptide hydrolase in erythrocytes

1. A peptide hydrolase has been partially purified from the soluble fraction of erythrocyte lysates. 2. The enzyme has a molecular weight of approximately 600,000 and hydrolyses the chymotrypsin substrate glutaryl-Gly-Gly-Phe-7-amido-4-methylcoumarin (pH optimum 7.0) and the trypsin substrate CBZ-Gly-Gly-Arg-2-naphthylamide. The two activities could not be separated by the purification procedure used. 3. The activity towards glutaryl-Gly-Gly-Phe-7-amido-4-methylcoumarin in rat reticulocytes was four times that in mature erythrocytes. 4. Activity was abolished by 10 microM p-hydroxymercuriphenylsulphonic acid.

Detergent-induced proteolysis of rabbit intestinal brush border vesicles

Proteolysis of brush border vesicle proteins is induced by detergent solubilisation. This proteolysis is selective in that some of the proteins are more susceptible than others. The rate of induced proteolysis is decreased by decreasing the temperature, has a minimum of about pH 6 and is effectively prevented by a combination of the protease inhibitors, EDTA, diisopropylfluorophosphate and iodoacetamide.

N-Acetylalanine aminopeptidase, a new enzyme from human erythrocytes

A new enzyme liberating N-acetylalanine from N-acetylalanine peptides with high specificity has been isolated from the cytosol of human erythrocytes. The N-acetylalanine aminopeptidase was purified by ammonium sulfate precipitation at 60% saturation, followed by chromatography on columns of Sephadex G-200, SP-Sephadex C-50, and DEAE-Sephadex A-50. About 2 000-fold enrichment was achieved from hemolyzed erythrocytes. The enzyme was homogeneous according to polyacrylamide disc electrophoresis and had a specific activity of 18.1 U/A280 unit. An apparent molecular weight of 300 000 +/- 15 000 was obtained from gel filtrations and was confirmed in the ultracentrifuge in "an active enzyme centrifugation" giving a corrected sedimentation value, s20w of 12 S. The pH optimum in triethanolamine/HCl buffer was around pH 8.3 with N-acetylalanine-4-nitroanilide as substrate, the Km was 0.616 mmol/l. The enzyme was stable between pH 6.0 to 8.0, but lost enzymic activity rapidly below pH 5 and with organic solvents. It is stabilized in a 0.1 M solution of ammonium sulfate. The activity was destroyed by high concentrations of chloromercuribenzoate and di(2-pyridyl)disulfide in an unspecific manner and could not be restored by cysteine. Various protein endoproteinase inhibitors are without influence on the enzymic activity. The enzyme exhibits an aminopeptidase-like activity with release of N-acetylalanine in order of decreasing activity from N-acetylalanine-4-nitroanilide, N-acetylalanyl-alanylalanine, N-acetylalanyl-tyrosyl-isoleucine, N-acetylalanylalanine, N-acetylalanyl-alanyl-alanylalanine, and N-acetylalanine ethyl ester. Several unacetylated peptides and alanine-4-nitroanilide as well as protein substrates were not hydrolyzed. The enzymic activity has not been found in the cytosolic compartment of highly purified human leucocytes. Its physiological function in erythrocytes is still unknown.

The stereospecific D-glucose transport activity of cholate extracts from human erythrocyte membranes

The glucose transport protein of human erythrocyte membranes was solubilized with cholate to facilitate rapid reconstitution and direct glucose transport measurements. This may simplify the isolation of the native glucose transporter. In most experiments the membranes were prepared from fresh blood within 8 h, frozen in liquid nitrogen and stored at -70 degrees C to minimize proteolytic degradation. Solubilization with 25 mM cholate in the presence of 200 mM NaCl at pH 8.4 for 12 min at room temperature gave a high D-glucose transport activity. The solubilized mixture contained 20% of the total membrane protein, only 6% of the polypeptides of molecular weight around 90000, 23% of the polypeptides of molecular weight around 55000, 30% of the phospholipids and at least 6% of the stereospecific D-glucose transport activity. At cholate concentrations up to 22 mM the ratio of solubilized phospholipids to cholate increased steeply, concomitant with an increase in solubilized activity. Above 30 mM cholate the activity diminished. At 4 degrees C the activity of the extract decreased rapidly within the first day and slowly during the next few days. The initial changes seem to have produced a fairly stable, but not native form or fragment of the transporter. When 20 mM EDTA and 5 mM dithioerythritol were included in the solubilization mixture a high activity was preserved for about one day.

Alterations in human erythrocyte shape and the state of spectrin and phospholipid phosphorylation induced by cholesterol depletion

Cholesterol depletion of erythrocytes, obtained after incubation with phosphatidylcholine vesicles, induces in most of the experiments: (1) a discocytestomatocyte transformation as observed by scanning electron microscopy; (2) a specific decrease in spectrin phosphorylation of intact erythrocytes; (3) an increase in lipid phosphorylation. It is concluded that the effect of cholesterol on erythrocyte shape is probably mediated through its action on the activity o of membrane-bound enzymes, proteases or kinases.

Elliptical erythrocyte membrane skeletons and heat-sensitive spectrin in hereditary elliptocytosis

Erythrocyte membranes (ghosts) and membrane skeletons (submembranous reticula of spectrin, actin, and protein 4.1 prepared by extracting ghosts with Triton X-100) from 15 patients with hereditary elliptocytosis (HE) were elliptical, which indicates that the primary defect responsible for the abnormal shape of these cells resides in the skeleton. The protein composition of HE skeletons was normal, but in three kindreds purified spectrin heterodimer from 7/7 HE patients was heat sensitive and denatured at 48.0 +/- 0.1 degrees C instead of 49.0 +/- 0.3 degrees C (P less than 0.0005). Heat sensitivity was detected by precipitation and, in the spectrin from one patient, by changes in circular dichroism. In one other kindred spectrin dimer from 3/3 patients denatured at the normal temperature. In two of the three kindreds with heat-sensitive spectrin, intact erythrocytes exhibited budding and fragmentation at the temperature at which spectrin denatured. In the third kindred spectrin was heat sensitive, but erythrocytes were not. The symptoms in the latter kindred were clinically more severe (hemolytic HE with spherocytosis) than in the other three (mild HE). We conclude that defects in the erythrocyte membrane skeleton may be a common feature of HE. As judged by heat denaturation of erythrocytes and purified spectrin dimer, three phenotypically distinct forms of HE exist, two of which are characterized by defective, heat-sensitive spectrin. It remains to be determined whether the molecular defect in spectrin responsible for heat sensitivity is the primary genetic defect responsible for HE.

Characterization of surface proteins and glycoproteins on red blood cells from mice infected with haemosporidia: Babesia rodhaini infections of BALB/c mice

Infection of intact (nu/+) or hypothymic (nu/nu) BALB/c mice with the lethal intra-erythrocytic parasite, Babesia rodhaini, induced several changes in the surface proteins of red cells from infected blood. Lactoperoxidase-catalysed radio-iodination was used to compare the surface proteins on normal mouse erythrocytes and the total red cells from infected blood at different levels of parasitaemia. At very low parasitaemia, when only 2.5% of the red cells contained parasites, we observed significant changes in the profile of radio-iodinated proteins separated by SDS-polyacrylamide gel electrophoresis. These changes included the appearance of a group of high molecular weight proteins, and a protein with an apparent molecular weight (Mr) of 60 000, both of which were absent from normal erythrocytes. The major labelled band on the erythrocyte surface (Mr 92 000) also appeared to be less heavily labelled during infection. The magnitude of these differences in surface proteins increased as the parasitaemia rose, until the new bands dominated the radioactivity profile with blood of greater than 50% parasitaemia. Several control experiments established that the radio-iodinated proteins were surface molecules on intact cells and that artifactual proteolysis did not contribute to the observed differences. The results suggest that changes in the surface proteins occur on all red cells in the blood of infected mice. The results of labelling the surface glycoproteins by oxidation with periodate or galactose oxidase, followed by NaB3H4 reduction, have varied with the isolate of B. rodhaini. With the isolate currently in use, no significant differences were observed in the labelled surface glycoproteins of normal erythrocytes and red cells from infected blood of high parasitaemia, whereas an earlier isolate exhibited a marked decrease of glycoprotein labelling of both infected and uninfected red cells.

Identification of proteolytic activities in the cytosolic compartment of mature human erythrocytes

Individual lysates from human erythrocyte suspensions, completely deprived of leucocytes and were assayed for a number of proteolytic activities using both naturally occurring and synthetic substrates. Removal of hemoglobin by batchwise DEAE-cellulose chromatography did not modify the complement of the various proteolytic activities which were then fractionated by means of chromatography on a column of DEAE-cellulose, followed by conventional techniques such as gel chromatography and preparative electrophoresis. This procedure allowed a number of proteinases to be identified in the erythrocyte cytosol while providing a tool for their selective though partial separation. The following peptidases were found to be present in the soluble fraction of mature human erythrocytes: (a) a neutral endopeptidase having an approximate molecular weight of 110 000; (b) three acidic endopeptidases, with pH optima between 2.5 and 3.5, showing molecular and functional properties almost identical with those of the three proteinases previously purified from solubilized erythrocyte membranes [Pontremoli et al. (1979) Biochem. J. 181, 559--568]; (c) two dipeptidylaminopeptidases whose molecular weights are around 80 000 and tentatively identified as dipeptidyl aminopeptidases II and III, respectively, on the basis of their substrate specificities and pH optima; (d) presumably two aminopeptidases, having an approximate molecular weight of 80 000 and classified as an aminopeptidase with broad substrate specificity and an aminopeptidase B, respectively. No evidence for any carboxypeptidase activity was found in the cytosolic compartment of mature human erythrocytes.