Partial purification and characterization of membrane-bound and cytosolic phosphatidylinositol-specific phospholipases C from murine thymocytes

Membrane-bound and cytosolic phosphatidylinositol (PI)-specific phospholipases C in murine thymocytes have been partially purified and characterized. The membrane-bound enzyme was extracted from microsomes with sodium cholate and purified by sequential column chromatographies on Sephadex G-100, heparin-Sepharose CL-6B, and Sephadex G-100. The cytosolic enzyme was purified from the cytosol by sequential column chromatographies on Sephadex G-100 and FPLC-Mono S. Specific activities of the membrane-bound enzyme and the cytosolic enzyme increased more than 1,800- and 1,400-fold, respectively, compared with those of microsomes and the cytosol. The molecular weights of the both enzymes were estimated to be about 70,000 by gel filtration. These purified enzymes also hydrolyzed phosphatidylinositol 4,5-bisphosphate (PIP2). At neutral pH and low Ca2+ concentrations, the membrane-bound enzyme hydrolyzed PIP2 in preference to PI and showed higher activity than the cytosolic enzyme. These activities were also affected differently by various lipids. For PIP2 hydrolysis, all lipids investigated except lysophosphatidylcholine enhanced the activity of the membrane-bound enzyme, while phosphatidylcholine (PC) and phosphatidylserine (PS) did not significantly affect the activity of the cytosolic enzyme. PC, PE, and PS inhibited the activities of the membrane-bound and cytosolic enzymes for PI hydrolysis. The physiological implications of these results are discussed.

Phosphatidylinositol-specific phospholipase C of murine lymphocytes

Phosphatidylinositol-specific phospholipase C (PI-phospholipase C) was found primarily in the cytosolic fraction of murine splenic lymphocytes. However, small but significant amounts of the activity of the enzyme were detected in the microsome and plasma membrane fractions. Both the cytosolic and membrane-bound phospholipases C specifically hydrolyzed inositol phospholipids, phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate. PI-Phospholipase C activity was detected in the cytosolic and microsome fractions from both T-cell-enriched and B-cell-enriched spleen cells. The membrane-bound enzyme was distinguishable from the cytosolic enzyme in the following properties. The cytosolic PI-phospholipase C showed optimal activity at pH 6.0 while the membrane-bound enzyme had two pH optima between pH 5.0 and 7.0. The activity of the cytosolic enzyme was first detected at 1 microM Ca2+, and maximum activity was observed at 100 microM Ca2+, while the membrane-bound PI-phospholipase C required higher Ca2+ concentrations, of millimolar order. The membrane-bound enzyme could hardly be extracted with 1 M NaCl but was extracted with 0.4% cholate.A portion of the membrane-bound PI-phospholipase C activity in the cholate extract was absorbed by concanavalin A-Sepharose and specifically eluted with an alpha-methylmannoside solution. The cytosolic enzyme, which was water soluble, did not bind to concanavalin A-Sepharose. Trypsinization of lymphocytes before subcellular fractionation caused a significant decrease in the PI-phospholipase C activity in the microsome fraction but almost no loss at all of the cytosolic enzyme activity.

The effect of food dye and other environmental substances on the host defense reaction in mice in relation to virus infection

Environmental substances were examined for their effect on interferon induction and delayed type hypersensitivity (DTH) responses in mice. Amaranth, safrole, phenacetin and nicotine suppressed the DTH response, and suppressed the serum interferon titers induced by virus infection. However, they did not affect the interferon titers which were induced by tilorone, a chemical inducer. The peak of interferon titer was 12 hours after infection with herpes simplex virus type 2 (HSV-2). Therefore, amaranth, safrole, phenacetin and nicotine were given to mice intraperitoneally 24 hours before, and 2 and 18 hours after infection with HSV-2. It was found that safrole and nicotine shortened the mean survival time of HSV-2 infected mice when they were given to mice 2 hours after virus inoculation. Amaranth and phenacetin showed similar effects. However it was not definite statistically. In biochemical and hematological tests, these four substances did not affect the functions of liver, kidney and carbohydrate metabolism in normal mice. These results suggest that substances which may often be taken into the body have the potential to affect the onset of virus infectious diseases as a result of the suppression of the host defense reaction.

Concanavalin A- and calcium-dependent phosphorylation of a protein of 80 kDa in mouse lymphocytes rendered permeable to exogenously added [gamma-32P]ATP

The phosphorylation of a protein of 80 kDa in permeable mouse lymphocytes is shown to be dependent both on exogenously added calcium and on concanavalin A. Lymphocyte plasma membranes are rendered permeable to exogenously added [gamma-32P]ATP and other small molecules by treatment with 20 micrograms/ml alpha-lysophosphatidylcholine for 1 min on ice. Treated cells are permeable to Trypan blue dye and exhibit phosphatidylinositol turnover in response to concanavalin A stimulation. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autofluorography, maximal phosphorylation of this protein occurs 5 min after addition of 20 microM calcium and 4 micrograms/ml concanavalin A. Exogenously added cyclic nucleotide cofactors do not enhance the phosphorylation of this 80 kDa protein, nor do inhibitors of calcium or calmodulin-dependent kinases suppress it, although in each case, other proteins are affected. In contrast, an inhibitor of the calcium-activated, phospholipid-dependent protein kinase (protein kinase C), H-7, strongly suppresses the phosphorylation of the 80 kDa protein. The tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol 13-acetate, a known activator of protein kinase C, significantly increases the phosphorylation of the 80 kDa protein. Finally, this protein is phosphorylated at a serine residue. These results taken together suggest that it is a substrate for protein kinase C. The possibility that it may also be an element of the concanavalin A signal transduction mechanism is discussed.

Inhibition of experimental pulmonary metastasis of mouse colon adenocarcinoma 26 sublines by a sialic acid:nucleoside conjugate having sialyltransferase inhibiting activity

The total and sialidase-releasable sialic acid contents of murine colon adenocarcinoma 26 sublines of high (NL-17) and low (NL-44) metastatic potential were found to be positively correlated with their ability to undergo metastasis. Furthermore, sialyltransferase activity of intact NL-17 cells was higher than that of NL-44 cells. These findings suggest that sialic acid on the cell surface may play a role in the metastasis of these cells. Therefore, the effect of a sialyltransferase inhibitor, 5-fluoro-2',3'-isopropylidene-5'-O-(4-N-acetyl-2,4-dideoxy-3,6,7,8-tetra -O -acetyl-1-methoxycarbonyl-D-glycero-alpha-D-galactooctapyranosyl)u ridine (Kl-8110), on the experimental lung metastasis of NL-17 or NL-44 cells was examined. Kl-8110 inhibited the transfer of sialic acid to its endogenous acceptor in NL-17 and NL-44 cells. NL-17 or NL-44 cells were injected into the tail veins of mice, and the metastasis-inhibiting activity of Kl-8110 was evaluated on the basis of both the lung weight and the number of pulmonary surface nodules about 3 wk after the tumor cell injection and of the survival ratio of mice inoculated with the tumor cells. Pretreatment of tumor cells with Kl-8110 together with i.v. injection of Kl-8110 caused significant inhibition of pulmonary metastasis of both NL-17 and NL-44 cells. Inhibition of metastasis and prolongation of survival were also observed on i.v. injection of Kl-8110 without pretreatment of the tumor cells with Kl-8110, but the degree of inhibition was lower than that in the case of the two treatments together. Kl-8110 itself had neither cytostatic nor cytotoxic effects on NL-17 and NL-44 but reduced the retention of tumor cells in the lungs. This antimetastatic effect of Kl-8110 may be due to modification of the tumor cell surface resulting from inhibition of sialyltransferase by Kl-8110. In addition, a beta-linked sialic acid:nucleoside conjugate (Kl-8111) and an equimolar mixture of Kl-8110 and Kl-8111 (Kl-414) also inhibited the metastatic ability of NL cells to the same extent as Kl-8110 did.

Invasive lobular carcinoma of the breast. An analysis of 29 cases

Twenty-nine cases of invasive lobular carcinoma were analyzed, based on three aspects of the histology: 1) cellular features such as a monotonous proliferation of uniform small cells, 2) a single file or targetoid arrangement, and 3) loss of cell cohesion or dissociation of tumor cells. Twenty-four tumors which fulfilled these three criteria were appraised as cases of conventional lobular carcinoma, in a classic sense, while five others were a variant of this tumor. Individual tumor cells of lobular carcinoma were estimated to be well differentiated, both morphologically and functionally, revealing well developed intracytoplasmic organelles and a high percentage of alpha-lactalbumin content in the cytoplasm. Nevertheless, the tumor itself was characterized by a lack of any particular structural differentiation in the arrangement of cells. Based on the observation of the histologic features, invasive lobular carcinoma was subclassified into three groups, in situ predominant, intermediate, and diffuse infiltrating and with a definite correlation to the age of the patient and to the prognosis. Validity of this classification indicates that lobular carcinoma progresses gradually, even in the invasive phase, and can be categorized as a slowly growing subset of mammary carcinoma.

Extremely well-differentiated adenocarcinoma ("adenoma malignum") of the cervix in a patient with Peutz-Jeghers syndrome

In a 29-year-old woman with the Peutz-Jeghers syndrome (PJS), an extremely well differentiated adenocarcinoma (adenoma malignum) of the uterine cervix was detected. The cervical lesion consisted of a polypoid mass, measuring 3.5 cm in greatest diameter, composed of extremely well differentiated tubules resembling those of the endocervical glands, yet containing a few Paneth cells. Immunohistochemical stains displayed cytoplasmic carcinoembryonic antigen in this tumor. The ovaries had no apparent abnormality. The diagnosis of the PJS was based on the presence of numerous hamartomatous polyps of the rectum and cutaneous pigmentation around the lips, fingers, and toes. The patient underwent a simple total hysterectomy and was subsequently treated with chemotherapy. In an 11 year follow-up, there has been no recurrence of the cervical tumor and she is currently well. The clinicohistopathologic differences of this cervical tumor in patients with and without PJS are briefly discussed.

Glandular or mucus-secreting components in squamous cell carcinoma of the esophagus

A review of 195 patients with carcinoma of the esophagus disclosed 41 cases (21.0%) with glandular and/or mucus-secreting components, in addition to the ordinary component of squamous cell carcinoma. These tumors could be grouped into three types according to representative histologic features of glandular and mucus-secreting portions: glandular type (23 cases), cribriform type (11 cases), and mucoepidermoid type (7 cases). The histologic features of the three types were reminiscent of those of adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma of salivary glands, respectively. Moreover, areas showing glandular or mucus-secreting differentiation were in greater part located in the submucosa and the lamina propria mucosae, thereby suggesting that such differentiation had arisen in the esophageal glands or their ducts. In all 41 cases, the ordinary element of squamous cell carcinoma, invasive, or noninvasive, was admixed in various proportions with the glandular components, indicating that this type of esophageal tumor had originated not only from the covering squamous epithelium but also from esophageal mucous-gland or ductal epithelium. The findings also support the concept of the field origin of carcinogenesis in esophageal carcinoma.

Glandular or mucus-secreting components in squamous cell carcinoma of the esophagus

A review of 195 patients with carcinoma of the esophagus disclosed 41 cases (21.0%) with glandular and/or mucus-secreting components, in addition to the ordinary component of squamous cell carcinoma. These tumors could be grouped into three types according to representative histologic features of glandular and mucus-secreting portions: glandular type (23 cases), cribriform type (11 cases), and mucoepidermoid type (7 cases). The histologic features of the three types were reminiscent of those of adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma of salivary glands, respectively. Moreover, areas showing glandular or mucus-secreting differentiation were in greater part located in the submucosa and the lamina propria mucosae, thereby suggesting that such differentiation had arisen in the esophageal glands or their ducts. In all 41 cases, the ordinary element of squamous cell carcinoma, invasive, or noninvasive, was admixed in various proportions with the glandular components, indicating that this type of esophageal tumor had originated not only from the covering squamous epithelium but also from esophageal mucous-gland or ductal epithelium. The findings also support the concept of the field origin of carcinogenesis in esophageal carcinoma.

Partial purification and characterization of phospholipid N-methyltransferases from murine thymocyte microsomes

Significant amounts of phospholipid N-methyltransferase activity in murine thymocytes were found to be distributed on the plasma membrane. The enzyme activity had an optimum pH of 9. The presence of divalent cations, Mg2+ (10 mM) or Ca2+ (1 mM), and EGTA separately in the assay had only a small effect on the enzyme activity. However, addition of both 10 mM Mg2+ and 1 mM Ca2+ increased the enzyme activity. The presence of two enzymes for each conversion of phosphatidylethanolamine (PE) to phosphatidylmonomethylethanolamine (PME) and PME to phosphatidylcholine (PC) was suggested by the result of the determination of the incorporated radioactivity into PME, phosphatidyldimethylethanolamine (PDE) and PC; the apparent Km values for S-adenosyl-L-methionine were 20 and 400-500 microM for the conversion of PE to PME and for the conversion of PME to PC they were 5 microM and 40 microM. S-Adenosyl-L-homocysteine (AdoHcy), a known inhibitor of enzymatic methylation, competitively inhibited [14C]methyl incorporation into total lipid. The apparent Ki value for AdoHcy was 44.7 microM. Two phospholipid N-methyltransferases were partially purified by extraction with sodium deoxycholate, gel filtration on Sephadex G-75, and affinity column chromatography on AdoHcy-Sepharose. One enzyme, mainly catalyzing the formation of PME, was purified approximately 1548-fold and the other catalyzing the formation of PDE and PC, was purified approximately 629- to 703-fold. However, the former still contained a little activity for PDE and PC formation and the latter contained a little activity for PME formation. In these partially purified phospholipid N-methyltransferase preparations, little contaminating protein O-carboxylmethyltransferase activity was observed; however, significant PC-phospholipase A2 activity was detected. This result may suggest that phospholipid N-methyltransferases associate with phospholipase A2 in the thymocyte plasma membrane.

Lectin-like molecules on the murine macrophage cell surface

Lectin-like molecules on the surface of murine peritoneal exudate macrophages induced by thioglycolate or an anti-tumor streptococcal preparation, OK-432, were investigated and isolated. Furthermore, their sugar-binding specificities and their role in macrophage-mediated tumor cytotoxicity were examined. A neoglycoprotein, D-galactose (Gal)-bovine serum albumin, bound to these murine peritoneal macrophages. This binding of Gal-bovine serum albumin was inhibited by D-galactose, and by complex-type oligosaccharides (unit B) and high mannose-type oligosaccharides (unit A) prepared from porcine thyroglobulin. When thioglycolate-elicited macrophages were activated by lipopolysaccharide and/or the culture supernatant of concanavalin A-activated mouse spleen cells, they became tumoricidal and the number of the lectin-like molecules on the macrophage surface was found to increase. Since the binding and cytotoxic activities of these tumoricidal macrophages toward tumor cells were partially inhibited by D-galactose, the D-galactose-binding lectin-like molecules on the surface of tumoricidal macrophages might play an important role in macrophage-mediated cytotoxicity. These lectin-like molecules were then isolated from solubilized murine peritoneal exudate cells labeled with pyridoxal 5'-phosphate and sodium [3H]borohydride by affinity chromatography on columns of asialo unit B oligosaccharide-Sepharose 4B and/or beta-D-galactose-Bio-Gel P-100. The proteins bound to the asialo unit B oligosaccharide-Sepharose 4B column and eluted specifically were found to have approximate molecular weights of 79 000 and 18 000, and the protein bound to and eluted from the beta-D-galactose-Bio-Gel P-100 column had an approximate molecular weight of 77 000. These isolated proteins bound to the surface of glutaraldehyde-fixed tumor cells, and their binding was inhibited by D-galactose and also by D-mannose. Since most of the 77 kDa protein bound to the asialo unit B oligosaccharide-Sepharose 4B, this protein was assumed to be identical with the 79 kDa protein. These results suggest that the lectin-like molecules on murine macrophages have wide specificity and that one lectin-like molecule can bind both D-galactose and D-mannose.

[Analysis of gastric biopsy specimens group III by a revised group classification]

A revised group classification of histology in gastric biopsy specimens was recently proposed by the Japanese Research Society For Gastric Cancer. The specimens judged as Group III by the revised classification contained; adenoma that used to be judged as Group III by the former classification, lesions difficult to distinguish between adenoma and carcinoma, lesions difficult to distinguish between atypical regenerative epithelium and carcinoma, and so on. Pathologists are requested to describe whether the lesion is adenoma or not and to consult with clinicians about the lesion in order to reduce the possibility that a case of well-differentiated adenocarcinoma is misdiagnosed as Group III by the revised classification.

Binding of bile acids with rat colon and resultant perturbation of membrane organization as studied by uptake measurement and 31P nuclear magnetic resonance spectroscopy

The mode of interaction of deoxycholate (DOC) or lithocholate (LC) with F344 rat colon was examined by measurements of uptake, 31P nuclear magnetic resonance (NMR) spectroscopy and observation of morphological changes. DOC as well as LC was taken up by the colon in a nonsaturable manner with respect to concentration and time, up to 30 min. None of several metabolic inhibitors reduced the uptake of the bile acids, nor did pretreatment of colon segments with chloroform-methanol (2:1, (v/v), heat or trypsin. Further, the bile acids were not transported by the colon against concentration gradients, and they were bound to both the mucosa and serosa equally. From these findings, it is concluded that the bile acids are transported in a passive manner, and no specific receptor for them is contained in colonic mucosa. The uptake of the bile acids by the colon varied with temperature and was related to the fluidity of the colonic membranes. The extent of uptake of dehydrocholate and taurocholate, which do not induce ornithine decarboxylase (ODC) activity, was almost the same as that of LC. The 31P NMR spectra of the colonic mucosal cells indicated that the proportion of the bilayer structure is increased by 0.5 mM DOC. Among a variety of bile acids examined, the extent of membrane alteration was in parallel with the extent of ODC induction. Treatment of the colonic mucosa with 0.5 mM DOC caused marked degeneration of the surface but not the deeper layers of the mucosa. Thus, physiological concentrations of bile acids influence the membrane organization of the colonic mucosa in a nonspecific manner that is possibly related to the tumor-promoting activity.

Simultaneous occurrence of primary carcinoma and chondrosarcoma in the liver. A case report and a review of the literature

We treated a 67-year-old man with primary carcinoma and sarcoma arising from the different areas of the cirrhotic liver. Histologically the carcinoma was of hepatocellular origin and the sarcoma consisted mainly of poorly differentiated mesenchymal cells partly with a chondrosarcomatous component. Among nine similar cases reported in the literature, only one was a rhabdomyosarcoma and the others were described simply as of spindle cell variety without evidence of mesenchymal differentiation. In the present case, the sarcoma consisted of mesenchymal cells with distinctive areas of unequivocal chondrosarcoma.

Incorporation of bile acid of low concentration into model and biological membranes studied by 2H and 31P NMR

We have analyzed the manner of incorporation of bile acid into lipid bilayers and resultant perturbation of the bilayer structure with lower bile acid/lipid ratios relevant to the physiological conditions (approximately 1 mM) by 2H and 31P NMR methods, as an aid to understanding the possible role as an endogenous tumor promoter in colon cancer besides the primary physiological function of solubilizing lipids. On the basis of the 2H quadrupole splittings of [6,6,7,7,8-2H5]deoxycholate and [11,11,12,12-2H4]chenodeoxycholate in the presence of lamellar multibilayers of egg yolk lecithin, these bile acids were found to be incorporated in such a manner that the B-D rings lie parallel with the normal of the bilayers when the ratio of the bile acid to lipid is low (less than 0.11). When the ratio is increased, these bile acid molecules are not dispersed entirely in the bilayer but aggregate to form micelles with lipids. Further, we studied the resultant perturbation of the multibilayers of egg yolk lecithin analyzed by using the 2H quadrupole splitting of [18,18,18-2H3]stearic acid as a probe and by 31P chemical shift anisotropy. We found that the bilayer structure is retained even at the bile acid-to-lipid ratio of 0.25, although a small amount of an isotropic phase appeared such as small vesicles and micelles. The molecular ordering of fatty acyl chains was rather enhanced by the presence of 1 mM deoxycholate in erythrocyte ghosts as seen from the 2H quadrupole splitting of [16,16,16-2H3]palmitic acid, although deoxycholate caused hemolysis in this condition. The former observation can be explained by the way the lipid-protein interaction is modified by deoxycholate located in the interface between the lipids and proteins.

CT's capability in detecting advanced gastric cancer

Upper GI series and CT scans of 23 patients with advanced gastric cancer were reviewed and correlated to determine CT's capability in detecting gastric tumors. The CT images of the gastric carcinomas revealed either a mass or thickening of the wall. These abnormalities were present in 78% of the cases whereas CT demonstrated a "mass" in 52%. The most difficult site for CT diagnosis of gastric cancer was the antrum. Diagnostic accuracy of CT in evaluating tumor invasion of adjacent structures is reportedly high. However, in the present study this was not necessarily true. In 4 of 5 patients whose gastric tumors proved unresectable, CT failed to reveal adjacent invasion. This suggests that CT is not always reliable in predicting surgical resectability.

The importance of determining stable glycosylated hemoglobin in diabetics: confusions are caused by the nomenclature of glycohemoglobin as HbA1C or HbA1 in its evaluation

Specimens of HbA1C from human hemolysate contain more than six minor components which cannot be separated by conventional methods. These components have differing characteristic properties and their levels fluctuate depending on the time the blood is drawn and the method of sample preparation used. HbA1C exhibits unreasonable fluctuation and unexpectedly high levels and is therefore not an accurate indicator of long-term blood glucose control. The six components of HbA1C were resolved by our new chromatographic technique using IEX-530, and designated by their eluting position and properties; HbF6, L-GHb7, St-GHb8, L-GHb9, Fr10, and Fr11. HbF6 was alkaline resistant. L-GHb7 and L-GHg9 were easily removed by treatment with saline or semicarbazide and increased after incubation with glucose. The level of L-GHb7 in the blood showed rapid and varied fluctuation on OGTT in both diabetics and control subjects. More than 2% HbF6 and L-GHb7 was present in 13.3% of the control group (n = 57) and in 51.4% of the IDDM group (n = 45). St-GHb8, which was a major component of HbA1C, was not affected by pretreatment with saline, semicarbazide or glucose in vitro. The level of St-GHb8 in the blood showed little change on OGTT. HbA1C, hitherto referred to as one stable component, is an incorrect term used to denote the index of long-term blood glucose control. It is important and warranted to use the level of stable glycohemoglobin (St-GHb8) in future determinations following proper analytical methods.

Mammary carcinoma with argyrophil cells

In a series of 253 cases of carcinoma of the breast, nonargentaffin, argyrophil cells were seen among the tumor cells in 27 cases (10.7%). An electron microscopic examination in one such case revealed dense cored secretory granules surrounded by a limiting membrane within the cytoplasm of the argyrophil tumor cells. Tumors with argyrophil cells, particularly when these cells were abundant, histologically showed a uniform appearance of relatively small constituent cells with oval or round nuclei of a regular size, forming solid alveolar nests or sheets. In one of these tumors, a delicate vascular stroma separated the sheets of tumor cells to form a ribbonlike pattern, simulating the feature of a carcinoid tumor. This tumor, however, is preferably interpreted at present as a mammary carcinoma with features of a carcinoid tumor, because of an incomplete characterization of argyrophil granules in the tumor cells. Other tumors with argyrophil cells were examples basically of ordinarily featured invasive ductal carcinoma. In a search for the origin of these cells, 99 breasts with various noncancerous lesions were examined; however, these argyrophil cells were never detected in any component of these mammary tissues.

Phospholipase A2 of chicken erythrocyte membranes

Chicken erythrocytes have been found to have at least two kinds of phospholipase A2. The first is a soluble enzyme from the cytosole fraction and has no calcium sensitivity. The second can be extracted from the plasma membrane fraction with the nonionic detergent Triton X-100. In this study the membrane-bound enzyme was partially purified by affinity chromatography on phosphatidylcholine-Sepharose, and its specific activity was increased 1100-fold compared with that of the cell homogenate without nuclei. It has an optimum pH of 8.5 and required calcium for maximum activity. It showed the specificity for both phosphatidylcholine and phosphatidylethanolamine, but reacted preferentially on the former substrate. Analysis by concanavalin A-Sepharose affinity chromatography revealed that the membrane-bound phospholipase A2 was retained on the resin and could be eluted specifically with a haptenic sugar, methyl alpha-D-mannopyranoside. The enzyme seems to be either a concanavalin A-binding glycoprotein or a part of a complex with certain concanavalin A-binding glycoproteins.

Induction of increased calcium uptake in liposomes having membrane proteins of chicken erythrocytes by S-adenosylmethionine

Liposomes having membrane proteins of chicken erythrocytes were prepared and the effect of S-adenosylmethionine on 45Ca2+ uptake into the liposomes was investigated. S-Adenosylmethionine, a donor of methyl groups in enzymatic methylation, induced an increase of 45Ca2+ uptake into the proteoliposomes with membrane proteins but not into the liposomes without membrane proteins. Increased release of 45Ca2+ from the inside of the proteoliposomes was also induced by S-adenosylmethionine. These increases of uptake and release of 45Ca2+ were inhibited by S-adenosylhomocystein, an inhibitor of enzymatic methylation. Furthermore, membrane proteins from chicken erythrocytes showed protein and phospholipid methyltransferase activities. The uptake of other materials, 3-0-[methyl-3H]glucose, alpha-[1-14C]aminoisobutyric acid, 42K+ and 54Mn2+, into the proteoliposomes was not increased by S-adenosylmethionine. These results suggest that enzymatic methylation of membrane components may have an important role in the regulation of calcium transport in the chicken erythrocyte membrane and this regulation is rather specific for calcium.

Establishment and characterization of continuous murine non-specific suppressor T cell lines

Normal mouse spleen cells were activated by Con A and suppressor T cells were enriched by the use of peanut agglutinin (PNA). Cells of the enriched suppressor T cell fraction were further cultured in a medium containing T cell growth factor (TCGF) and the suppressor T cell lines were established. These cell lines have been growing in culture for more than one year and retained surface characteristics of Thy-1+, Lyt-1-, 2- and bear receptor sites for PNA. The suppressor clones exerted an inhibitory effect on in vitro antigen specific and antigen nonspecific PFC responses. The culture supernatant of these clones had a suppressive effect on the in vitro humoral responses, indicating that a soluble factor mediates at least partly the suppressive activity of the antigen nonspecific suppressor T cells. Moreover, it was revealed that the suppressor cells must exist at an early stage of PFC culture to exert their activity.