High dietary iodine intake may contribute to the low death rate from COVID-19 infection in Japan with activation by the lactoperoxidase system

We draw the attention of readers and governments to the death rate from coronavirus disease 2019 in Japan, continuing as a fraction of that experienced by many other developed nations. We think this is due to the activity of the powerful, protective lactoperoxidase system (LPO) which prevents serious airborne infections. The LPO system requires iodine, which is liberally provided by the typical Japanese diet but lacking in many others. One might consider the Japanese experience an incredibly large, open-label study exhibiting the preventative power of a high-iodine diet. We predict this favourable trend will continue for Japan because deadly variants of the severe, acute respiratory syndrome coronavirus 2 will be with us, forever.

Synthesis and Characterization of Biotene: A New 2D Natural Oxide From Biotite

In this work, the synthesis and characterization of ultrathin metal oxide, called biotene, using liquid-phase exfoliation from naturally abundant biotite are demonstrated. The atomically thin biotene is used for energy harvesting using its flexoelectric response under multiple bending. The effective flexoelectric response increases due to the presence of surface charges, and the voltage increases up to ≈8 V, with a high mechano-sensitivity of 0.79 V N^-1 for normal force. This flexoelectric response is further validated by density functional theory (DFT) simulations. The atomically thin biotene shows an increased response in the magnetic field and thermal heating. The synthesis of two-dimensional (2D) metal-oxide biotene suggests a wealth of future 2D-oxide material for energy generation and energy harvesting applications.

Glutathione utilization protects Streptococcus pneumoniae against lactoperoxidase-derived hypothiocyanous acid

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia, resulting in more than one million deaths each year worldwide. This pathogen generates large amounts of hydrogen peroxide (H₂O₂), which will be converted to hypothiocyanous acid (HOSCN) by lactoperoxidase (LPO) in the human respiratory tract. S. pneumoniae has been shown to be more resistant to HOSCN than some bacteria, and sensitizing S. pneumoniae to HOSCN may be a novel treatment strategy for combating this deadly pathogen. In this study we investigated the role of the low molecular weight thiol glutathione in HOSCN resistance. S. pneumoniae does not synthesize glutathione but imports it from the environment via an ABC transporter. Upon treatment of S. pneumoniae with HOSCN, bacterial glutathione was reversibly oxidized in a time- and dose-dependent manner, and intracellular proteins became glutathionylated. Bacterial death was observed when the reduced glutathione pool dropped below 20%. A S. pneumoniae mutant unable to import glutathione (ΔgshT) was more readily killed by exogenous HOSCN. Furthermore, bacterial growth in the presence of LPO converting bacterial H₂O₂ to HOSCN was significantly impeded in mutants that were unable to import glutathione, or mutants unable to recycle oxidized glutathione (Δgor). This research highlights the importance of glutathione in protecting S. pneumoniae from HOSCN. Limiting glutathione utilization by S. pneumoniae may be a way to limit colonization and pathogenicity.

Xanthine oxidase-lactoperoxidase system and innate immunity: Biochemical actions and physiological roles

The innate immune system in mammals is the first-line defense that plays an important protective role against a wide spectrum of pathogens, especially during early life before the adaptive immune system develops. The enzymes xanthine oxidase (XO) and lactoperoxidase (LPO) are widely distributed in mammalian tissues and secretions, and have a variety of biological functions including in innate immunity, provoking much interest for both in vitro and in vivo applications. The enzymes are characterized by their generation of reactive oxygen and nitrogen species, including hydrogen peroxide, hypothiocyanite, nitric oxide, and peroxynitrite. XO is a major generator of hydrogen peroxide and superoxide that subsequently trigger a cascade of oxidative radical pathways, including those produced by LPO, which have bactericidal and bacteriostatic effects against pathogens including opportunistic bacteria. In addition to their role in host microbial defense, reactive oxygen and nitrogen species play important physiological roles as second messenger cell signaling molecules, including cellular proliferation, differentiation and gene expression. There are several indications that the reactive species generated by peroxide have positive effects on human health, particularly in neonates; however, some important in vivo aspects of this system remain obscure. The primary dependence of the system on hydrogen peroxide has led us to propose it is particularly relevant to neonate mammals during milk feeding.

Identifying and overcoming the effect of mass transfer limitation on decreased yield in enzymatic hydrolysis of lignocellulose at high solid concentrations

Cellulose conversion decreases significantly with increasing solid concentrations during enzymatic hydrolysis of insoluble lignocellulosic materials. Here, mass transfer limitation was identified as a significant determining factor of this decrease by studying the hydrolysis of delignified corncob residue in shake flask, the most used reaction vessel in bench scale. Two mass transfer efficiency-related factors, mixing speed and flask filling, were shown to correlate closely with cellulose conversion at solid loadings higher than 15% DM. The role of substrate characteristics in mass transfer performance was also significant, which was revealed by the saccharification of two corn stover substrates with different pretreatment methods at the same solid loading. Several approaches including premix, fed-batch operation, and particularly the use of horizontal rotating reactor were shown to be valid in facilitating cellulose conversion via improving mass transfer efficiency at solid concentrations higher than 15% DM.

[In vitro study of the effect of a lactoperoxidase-peroxidase-thiocyanate system with iodine on the cariogenicinity of streptococcus mutans]

OBJECTIVE

This study aimed to investigate the effect of a lactoperoxidase-peroxidase-thiocyanate (LPO-H2O-SCN-) system with different concentrations of iodine (I-) on Streptococcus mutans (S. mutans), particularly on various parameters, including growth, adhesion, glucosyltransferase (GTF) enzyme activity, and insoluble exopolysaccharide synthesis.

METHODS

S. mutans ATCC 25175 was used as experimental species. Clonal formation unit (CFU) were counted to investigate the inhibitory effect on bacterial growth. The inhibition rate of bacterial adherence was calculated to analyze the effect on adhesion. Anthrone method was used to determine the content of insoluble exopolysaccharides and the amount of reducing saccharides. GTF activity and enzyme activity were then determined.

RESULTS

The inhibitory ability of the LPO-H2O2-SCN- system with I- on the cariogenicinity of S. mutans was strengthened as I- concentration was increased. At I- concentration > or = 100 micromol x L(-1) the antibacterial effects were significantly increased compared with those of the control group (P < 0.05). At I- concentration > or = 1,000 micromol x L(-1), the antibacterial effects were significantly improved compared with those of the group with SCN-only (P < 0.05). At I- concentration > or = 100 micromol x L(-1), the inhibition rate of bacterial adherence was > 50%; insoluble exopolysaccharide synthesis and GTF enzyme activity were reduced (P < 0.05).

CONCLUSION

The antibacterial effects of the LPO-H2O2-I- system were enhanced by adding I- to overcome the antagonistic effect of physiological SCN- concentration. LPO-H2O2-SCN- system with different concentrations of I- showed statistically significant inhibitory effects on growth, adhesion, insoluble exopolysaccharide synthesis, and GTF enzyme activity.

Efficacy of the BioXtra dry mouth care system in the treatment of radiotherapy-induced xerostomia

INTRODUCTION

Xerostomia is a common complication of radiotherapy for head and neck cancer. Symptomatic treatment consists of stringent oral hygiene to prevent oral infections and saliva substitutes to increase comfort. The aim of the study was to evaluate the clinical effectiveness of the BioXtra (BX) dry mouth care system.

MATERIALS AND METHODS

A xerostomia questionnaire consisting of 3 parts (xerostomia symptom score, quality of life (QoL) survey and visual analogue scale (VAS)) was completed by 34 patients suffering from radiation-induced xerostomia, before and after 4 weeks of treatment with the BioXtra moisturizing gel, toothpaste and mouthwash.

RESULTS

The BioXtra products significantly diminished the most common symptoms of xerostomia. Mean VAS score at the start of treatment was 59.8. After treatment, this decreased to 36.4 (p < 0.001). Twenty-six patients (77%) responded to treatment, 11 of these patients (32%) reported a major improvement. Quality of life significantly improved under treatment: mean QoL score at the start was 59.4; this increased to 70.5 (p < 0.001). None of the 34 patients reported any adverse effects and all but 1 patient found the BX dry mouth care system easy to use.

CONCLUSIONS

The results of this study suggest that the BioXtra dry mouth care system is effective in reducing the symptoms of radiation-induced xerostomia and improving the quality of life of xerostomia patients, even if a proportion of the benefit is due to a placebo effect. However, further research is necessary to evaluate the efficacy of BioXtra on oral health.

Radiolabeling of amyloid-beta peptides

Nowadays, a wide variety of protocols for labeling proteins is available. However, radiolabeling remains one of the most powerful, sensitive and accurate methods to trace and quantitate proteins. Additionally, radiolabeling techniques are steadily gaining importance for diagnosis and treatment in nuclear medicine. There is a considerable number of radioisotopes, but only some are commonly used for basic biomedical research. Among them, the iodine radioisotopes (gamma-emitters) have several advantages for the labeling of proteins. This chapter focuses on radioiodination protocols for amyloidogenic peptides, using the Abeta peptides as a paradigm. The chloramine T, Iodo-Gen, and lactoperoxidase methods can be successfully applied to radioiodination of different amyloid peptides as long as free tyrosyl (or histidyl) groups are avail-able. However, these methods differ in their yield and the degree of oxidative damage conferred to labile peptides. When no tyrosines are available, the Bolton-Hunter methodology can be used. The labeling by the tyramine-cellobiose ligand trapping method is applicable to the study of cellular uptake and catabolism of amyloid peptides.

Development of a laboratory scale clean-in-place system to test the effectiveness of "natural" antimicrobials against dairy biofilms

A laboratory scale system, partially reproducing dairy plant conditions, was developed to quantify the effectiveness of chlorine and alternative sanitizers in reducing the number of viable bacteria attached to stainless steel surfaces. Stainless steel tubes fouled in a continuous flow reactor were exposed to a standard clean-in-place regime (water rinse, 1% sodium hydroxide at 70 degrees C for 10 min, water rinse, 0.8% nitric acid at 70 degrees C for 10 min, water rinse) followed by exposure to either chlorine (200 ppm) or combinations of nisin (500 ppm), lauricidin (100 ppm), and the lactoperoxidase system (LPS) (200 ppm) for 10 min or 2, 4, 8, 18, or 24 h. There was significant variation in the effectiveness of the alkaline-acid wash steps in reducing cell numbers (log reduction between 0 and 2). Following a 10-min treatment, none of the sanitizers significantly reduced the number of attached cells. Two hours of exposure to chlorine, nisin + the LPS, or lauricidin + the LPS achieved 2.8, 2.2, and 1.6 log reductions, respectively. Exposure times > 2 h did not further decrease the number of viable bacteria attached to the stainless steel. The effectiveness of combinations of nisin, lauricidin, and the LPS was similar to that of chlorine (P > 0.05), and these sanitizers could be used to decontaminate the surfaces of small-volume or critical hard-to-clean milk processing equipment.

Studies on the iodination of a ras protein and the detection of ras polymers

Several methods for the iodination of recombinant v-H-ras protein were compared. The Iodobead method gave greatest incorporation of radioactivity with minimal modification of the ras protein. Upon treatment of the ras protein with [125I] Nal and an Iodobead, radioactivity was initially incorporated into a 22 kDa species with a pl of 5.2, then predominantly into a 23 kDa species with a pl of 5.4. The specific activity of [125I]ras was 6 x 10(6) cpm/pmol total ras protein. Iondination did not alter the biological activity of the ras protein as judged by its ability to bind GTP gamma S and induce maturation of Xenopus laevis oocytes. It is concluded that while iodination alters the apparent molecular weight and pI of ras, presumably by the oxidation of one or more classes of amino acids, this does not affect the biological function of the protein. The ras protein, radioactively-labelled with iodine using the Iodobead method, should be suitable for studies of protein-protein interactions involving ras. Treatment of iodinated ras with the chemical cross-linking agent disuccinimidyl suberate revealed the presence of several minor high molecular weight protein species. This result shows that, in a dilute solution of purified ras protein, the monomeric form is in equilibrium with small amounts of polymeric forms.

A method for selective radiolabeling of lung endothelium plasmalemmal vesicles, in situ

Albumin-gold complex (Alb-Au) was previously shown to bind selectively to plasmalemmal vesicles of capillary endothelium. Based on these findings, as well as on the ability of lactoperoxidase (LPO) to mediate the radioiodination of proteins, we have prepared a complex of gold particles bearing both albumin and anionized lactoperoxidase (Alb-Au-aLPO). The complex had a pI of 5.8, largely preserved aLPO enzymatic activity (approximately 74%), and was able to catalyze protein radioiodination. Upon washing out the blood, the complex was perfused in the mouse lung, the excess tracer removed, and a Na125I/H2O2 solution was introduced in the vasculature. After extensive washing, lung fragments were processed for either electron microscopy (EM), or to prepare a membrane-enriched fraction. In control experiments, lungs were perfused with native LPO (pI 9.3), or with a LPO-Affi Gel conjugate and further radioiodinated as described for Alb-Au-aLPO. By EM, it was found that both in tissue and in the isolated membrane fraction, only Alb-Au-aLPO labeled markedly and preferentially some uncoated pits and most plasmalemmal vesicles. Analysis by SDS-PAGE and autoradiography of a membrane-enriched fraction prepared from lungs perfused with Alb-Au-aLPO had some major identified 125I-labeled polypeptides of apparent molecular masses of 16, 18, 31, 36, 55, and 77 kDa. A different subset of polypeptides was labeled in lungs perfused with LPO, whereas after administration of LPO-Affi Gel the major radiolabeled polypeptides had a molecular mass of 33, 55 kDa and several peptides in the range of 77 to 160 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of interleukin-10 receptors on human and mouse cells

Human interleukin (IL)-10 is a pleiotropic cytokine acting on a variety of immune cells. Here we show that the protein can be enzymatically iodinated to high specific radioactivity with retention of biological activity. The radiolabeled ligand binds specifically to its receptor in several mouse and human cell lines, notably human B-lymphoma line JY and mouse mast cell line MC/9. Human IL-10 apparently binds as a dimer to a single class of receptor in both the JY and MC/9 cell lines with a Kd in the 50-200 pM range. Interestingly, mouse IL-10 was capable of blocking binding of human IL-10 to mouse but not human cells. There appears to be at most only a few hundred IL-10 receptors/cell for both mouse and human cell lines examined. Chemical cross-linking of the radioiodinated hIL-10 to JY and MC/9 cells revealed a common protein complex with an apparent molecular mass of about 97 kDa. Additional high molecular weight complexes were detected with JY but not MC/9 cells.

Reactions of radiolytically-generated superoxide anion with higher oxidation states of lactoperoxidase

The time-courses of absorption changes after pulse radiolysis of oxygen-saturated solution of lactoperoxidase have been studied. Radiation-generated superoxide reduces compounds I to II. The results suggest that superoxide anion reacts also with compound II of lactoperoxidase; however, the reduction of the heme iron has not been observed. A possible reaction pathway of compound II in the presence of superoxide anion is discussed.

Determination of the sidedness of the C-terminal region of the gastric H,K-ATPase alpha subunit

It cannot be predicted from hydropathy analysis whether the C-terminal end of the alpha subunit of the gastric H,K-ATPase is cytoplasmic or extracytoplasmic. The sideness of the C-terminal amino acids was determined by taking advantage of the two C-terminal tyrosines in the primary sequence of the enzyme. Intact, cytoplasmic side out vesicles derived from hog gastric mucosa or detergent solubilized vesicles were iodinated by the lactoperoxidase method and then the C-terminal amino acids hydrolyzed by carboxypeptidase Y. The alpha and beta subunits were separated by SDS gel electrophoresis. The level of iodination of the alpha subunit following solubilization was about three fold greater than when intact vesicles were iodinated, and the beta subunit was iodinated only when solubilized enzyme was used. Carboxypeptidase Y removed 28 +/- 4% of the radioactivity from the alpha subunit iodinated in intact vesicles. These data are consistent with a cytoplasmic location of the C-terminal amino acids of the alpha subunit and with a mostly extracytoplasmic location of the amino acids of the beta subunit.

Self-labeling of human polymorphonuclear leucocyte myeloperoxidase with 125iodine

In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with 125Iodine:chloramine T, lactoperoxidase, and an original technique of 'self labeling' based on the ability of the enzyme to oxidize and bind 125I in the presence of H2O2. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 microCi/micrograms MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (less than or equal to 3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits.

Localization and characterization of the acrosomal antigen recognized by GB24 on human spermatozoa

GB24, a mouse monoclonal antibody, recognizes a trophoblast-leukocyte cross-reactive antigen (TLX), which is likely identical to the membrane cofactor protein (MCP), a complement regulatory protein. GB24 reacts also with a human acrosomal sperm antigen (Fénichel et al.: J Reprod Fertil 87:699-706, 1989). By immunofluorescence or immunoperoxidase, testicular, epididymal, and ejaculated spermatozoa were found to be positive after fixation by acetone. Motile, suspended spermatozoa became positive only through conditions known to induce acrosome reaction (A23187, follicular fluid, contact with oocytes). Ultrastructural studies with immunogold staining localized this protein on the inner acrosome membrane and in the acrosomal content. By SDS-polyacrylamide gel electrophoresis, GB24 immunoprecipitated a unique protein of 48 kDa from capacitated and A23187-induced spermatozoa under reducing conditions. No cross-reactivity was found with mouse, boar, or ram spermatozoa. Localization of this human sperm antigen recognized by GB24 and its similarity with the TLX-MCP family antigens would suggest a possible role of this molecule during fertilization in sperm-egg binding or immune protection.

The effect of trypsin on CD1a molecule of human thymocytes

The cortical thymocytes expressed at least three distinct cell-surface differentiation antigens. CD1a (Mr 49,000), CD1b (Mr 45,000) and CD1c (Mr 43,000) which are non-covalently attached to beta 2-microglobulin. In the present study, we confirm the presence of two out of the three CD1 molecules on epidermal Langerhans cells by biochemical analysis. Furthermore some CD1a monoclonal antibodies immunoprecipitated an additional molecule with an apparent relative mass of 27,000 from Langerhans cell-enriched epidermal cell lysates and not from fresh iodinated thymocyte lysates. From trypsin-treated thymocyte lysates, this low molecular weight protein was considered as a cleavage product of Mr 49,000 molecule (CD1a molecule) by this enzyme which is used to obtain epidermal cell suspensions. This Mr 27,000 was found to content one N-linked oligosaccharide residue by endoglycosidase F treatment. On CD1-expressing cells (thymocytes and Langerhans cells) it would be tempting to take advantage of the sensitivity of CD1a molecule to trypsin in order to precise the structure/function relationship of CD1a antigen.

Enhanced in vitro cytotoxicity of 1,3-bis-(2-chloroethyl)-1-nitrosourea or buthionine sulfoximine combined with a reactive oxygen-generating enzyme immunotoxin

The glutathione inhibitor drugs, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and buthionine sulfoximine (BSO), were tested in vitro in order to assess their cytotoxic effectiveness when combined with an enzyme immunotoxin (eIT) composed of a T-cell reactive monoclonal antibody (mAb) 097 coupled to the reactive oxygen-generating enzyme, glucose oxidase (GO) (EC 1.1.3.4). As targets of this eIT we used mature human T-cells or leukemia cells that expressed the 097 epitope. We found that treatment of the cells with subtoxic amounts of mixtures of both a drug and the 097 eIT markedly potentiated cytotoxicity compared to either drug or eIT alone.

Coordination geometry of heme in lactoperoxidase: pH-dependent 1H relaxivity and optical spectral studies

Molar relaxivity of water proton in lactoperoxidase solution was studied as a function of pH in the range of 2-13 by spin-lattice relaxation time measurements on a Bruker AM 500 MHz nuclear magnetic resonance (NMR) spectrometer. It was shown by comparison with the molar relaxivities of met myoglobin (Mb) and horseradish peroxidase (HRP) solutions that the sixth coordination position of the heme pocket in lactoperoxidase (LPO) is vacant. Distance of the water proton in the heme pocket from ferric ion was deduced to be 2.7, 3.6 and 4.3 A for Mb, HRP, and LPO, respectively. Acid-alkaline transition for met myoglobin, horseradish peroxidase, and lactoperoxidase determined from the pH dependence of changes in the Soret absorptions were found to be characterized by pK of 8.8, 10.9, and 12.1, respectively. Proton NMR of LPO at pH = 12.2 was found to have single broad resonance considerably upfield shifted as compared to that of LPO at neutral pH. By comparison with the proton NMR of HRP and Mb at pH greater than their respective pK of acid-alkaline transition, the upfield shifted proton resonance of LPO at pH = 12.2 was assigned to be due to low-spin LPO.

A unique subset of developmentally regulated surface proteins turns over rapidly during fusion of the L6 rat myoblast cell line

We have previously identified several developmentally regulated surface polypeptides in the L6 rat myoblast cell line, on the basis of their susceptibility to lactoperoxidase catalyzed iodination. An analysis of the turnover rates of these polypeptides now indicates that while the bulk of the iodinated polypeptides have a half-life of 20-30 h, four low-molecular-weight polypeptides have half lives of 2-7 h. The half-lives of all of the rapid turnover class surface polypeptides were greatly increased in cultures where fusion was inhibited by chloroquine and in nonfusing variants of the L6 cell line. In contrast, inhibition of fusion by the metalloendoprotease inhibitor 1, 10-phenanthroline did not alter the turnover of any iodinatable surface proteins. We propose that some or all of the rapid turnover class of polypeptides may be surface receptors which control cell surface alterations involved in the acquisition of fusion competence or in fusion itself.

Oxidation of the substituted catechols dihydroxyphenylalanine methyl ester and trihydroxyphenylalanine by lactoperoxidase and its compounds

The reactions of native lactoperoxidase and its compound II with two substituted catechols have been investigated by ESR spin stabilization and spin trapping and by rapid scan and conventional spectrophotometric techniques. The catechols are Dopa methyl ester (dihydroxyphenylalanine methyl ester) and 6-hydroxy-Dopa (trihydroxyphenylalanine). o-Semiquinone radicals are formed in the anaerobic reaction of Dopa methyl ester with hydrogen peroxide catalyzed by native lactoperoxidase. The comparable anaerobic reaction of 6-hydroxy-Dopa appears to produce hydroxyl radicals in an unusual reaction. Compound II is reduced back to native lactoperoxidase by both catechols. The reaction between Dopa methyl ester and compound II undergoes an oscillation. The results on the overall lactoperoxidase cycle indicate two successive one-electron reductions of the peroxidase intermediates back to the native enzyme. The resulting free radical formation of o- and p-semiquinones and subsequent formation of stable quinones and Dopachromes is dependent upon the stereochemical arrangement of the catechol hydroxyl groups.

The heme environment of ovoperoxidase as determined by optical spectroscopy

Native ovoperoxidase exhibited an optical absorption spectrum with certain similarities to lactoperoxidase, but not horseradish peroxidase, over the pH range 4.5-11.5. Ovoperoxidase had three distinct spectral forms dependent on pH, with transitions at apparent pKa values of 6.6 and 3.0. Complexes of ovoperoxidase with CN-, N3-, F-, or when reduced and ligated to carbon monoxide, CN-, or pyridine, were distinct from other peroxidases. Ovoperoxidase formed two specific and different spectral derivatives at pH 6.0 and 8.0, either in the native state, or when combined with CN-, when reduced, or when reduced and ligated to CN-. The position of the Soret band when mixed with near-stoichiometric amounts of H2O2. This cycling was inhibited by phenylhydrazine, 3-amino-1,2,4-triazole, or low pH (less than or equal to 6). Compound II was formed when ovoperoxidase was mixed with ethyl hydrogen peroxide in a 1:3 ratio, but not with H2O2. With a great excess of H2O2, Compound III was formed at pH 8.0; at pH 6.0 or below, the Soret band shifted slightly with excess of H2O2, but Compound III was never formed. Even when ovoperoxidase was bound to proteoliaisin (Weidman, P. J., and Shapiro, B. M. (1987) J. Cell Biol. 105, 561-567), ovoperoxidase exhibited spectral characteristics of the free enzyme.

A nuclear Overhauser effect investigation of the molecular and electronic structure of the heme crevice in lactoperoxidase

The proton homonuclear nuclear Overhauser effect, NOE, in conjunction with paramagnetic-induced dipolar relaxation, is utilized to assign resonances and to probe the molecular and electronic structures of the heme cavity in the low-spin cyanide complex of resting-state bovine lactoperoxidase, LPO-CN. Predominantly primary NOEs were detected in spite of the large molecular weight (approximately 78 x 10(3)) of the enzyme, which demonstrates again the advantage of paramagnetism suppressing spin diffusion in large proteins. Both of the nonlabile ring protons of a coordinated histidine are located at resonance positions consistent with a deprotonated imidazole. Several methylene proton pairs are identified, of which the most strongly hyperfine-shifted pair is assigned to the unusual chemically functionalized 8-(mercaptomethylene) group of the prosthetic group [Nichol, A. W., Angel, L. A., Moon, T., & Clezy, P. S. (1987) Biochem. J. 247, 147-150]. The large 8-(mercaptomethylene) proton contact shifts relative to that of the only resolved heme methyl signal are rationalized by the additive perturbations on the rhombic asymmetry of the functionalization of the 8-position and the alignment of the axial histidyl imidazole projection along a vector passing through pyrrole A and C of the prosthetic group. Such a stereochemistry is consistent with the resolution of only a single heme methyl group, 3-CH3, as observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative analysis of surface components of adult, micro-filariae and infective larvae of Brugia malayi

A comparative analysis of surface proteins of adult, microfilariae and infective larvae of Brugia malayi, the human filarial parasite, has been carried out using IODOGEN (1,3,4,6-tetrachloro-3,alpha 6 alpha-diphenyl-glycoluril) and lactoperoxidase methods. SDS-polyacrylamide gel electrophoretic and autoradiographic analyses revealed the presence of 9 proteins (15-200 kDa) in adults, while microfilariae and infective larvae showed 8 and 6 proteins (15-120 kDa), respectively. The pattern of proteins radiolabelled by IODOGEN method was very similar to that of proteins labelled by the lactoperoxidase method. Since these proteins are released by the protease treatment of whole parasites, they are likely to be present on the surface of the parasite.

Purification and characterization of human salivary peroxidase

Human salivary peroxidase (SPO) has been purified to homogeneity by subjecting human parotid saliva to immunoaffinity, cation exchange, and affinity chromatography. These procedures resulted in a 992-fold purification of the enzyme. When purified SPO was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), three Coomassie stainable bands were apparent, all of which stained positive for enzyme activity. The apparent molecular weights of the three bands were 78,000, 80,000, and 280,000 as analyzed by SDS-PAGE. Reduction with 2-mercaptoethanol resulted in a decreased mobility of these bands, and enzyme activity could no longer be detected on the gels. The SPO preparation had the characteristic peroxidase heme spectrum in the range 405-420 nm. The ratio between the absorbance of the Soret band (412 nm) and the absorbance at 280 nm was 0.81. The enzyme activity was inhibited by the classical peroxidase inhibitors cyanide and azide. Salivary peroxidase is similar to bovine lactoperoxidase (LPO) in amino acid composition, in ultraviolet and visible spectrum, in reaction with cyanide, in susceptibility to 2-mercaptoethanol inactivation, and in thermal stability. The two enzymes differ in carbohydrate composition and content. SPO contains 4.6% and LPO 7% total neutral sugars. The ratio of glucosamine to galactosamine is 2:1 in SPO and 3:1 in LPO. SPO contains mannose, fucose, and galactose in a molar ratio of 1.5:1.5:1.0, while the ratio was 14.9:0.5:1.0 in LPO. Glucose was present in both preparations in minor amounts. The concentration of azide required for 50% inhibition of enzyme activity was 20-fold greater for LPO than for SPO.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effect of iodination of ovotransferrin and its two half-molecule domains on binding to transferrin receptors on chick embryo red blood cells

Iodination of the C-terminal half-molecule domain of ovotransferrin (OTF) causes a significant reduction in binding to transferrin receptors on chick reticulocytes when compared to the binding observed with holo-OTF or the N-terminal half-molecule domain. (In such studies binding of iodinated half-molecule is measured in the presence of equimolar unlabelled complementary half-molecule). In particular iodination of the C-terminal half-molecule domain by the solid-phase reagent Iodogen resulted in half the binding found when ICl was used. The iodinated N-terminal half-molecule domain labelled by either Iodogen or ICl showed consistently higher binding than was observed with the C-terminal half-molecule or Fe2OTF. Although the molecular basis for the reduced binding of these proteins relative to the N-terminal half-molecule has not been definitively established, the implication is that there is a Tyr in the C-terminal domain which is involved in receptor recognition and binding. Addition of one or more bulky iodine atoms to the Tyr interferes with the interaction. Tryptic peptide maps of unlabelled holo-OTF and half-molecule domains and of the half-molecule domains labelled by both ICl and Iodogen are presented. The maps indicate limited access of the tyrosine residues to iodination especially in the C-terminal half-molecule domain. Equilibrium binding experiments have been carried out to compare the Kd (the apparent dissociation constant for the interaction between OTF and the transferrin receptors on chick-embryo red blood cells) with the Bmax, (binding at infinite free-ligand concentration) for Fe2OTF labelled using ICl, Iodogen, Enzymobeads and Chloramine-T. The effect of labelling Fe2OTF by Bolton-Hunter reagent has also been assessed. These studies show that ICl appears to be the reagent of choice for labelling Fe2OTF and its half-molecule domains.

Lactoperoxidase haem, an iron-porphyrin thiol

The haem prosthetic group of lactoperoxidase can be prepared from the enzyme in high yield by reductive cleavage with mercaptoethanol in 8 M-urea under mild conditions. The product yields porphyrins, after removal of iron, which show visible spectroscopic properties similar to protoporphyrin but are considerably more polar. In the presence of iodoacetamide, a different product is obtained by reductive cleavage. The proton n.m.r. and mass spectra of this compound indicate that the prosthetic group of the enzyme is the iron complex of 18-mercaptomethyl-2,7,12-trimethyl-3,8-divinylporphyrin-13,17-d ipropionic acid. It is proposed that the unusual strength of binding of the prosthetic group to the apoprotein is due to formation of a disulphide bond from a cysteine residue to the porphyrin thiol.

Radioreceptor assay of human prolactin using rabbit mammary receptors

The purpose of this work is to develop the procedures for the preparation of the reagents suitable for the radioreceptor assay (RRA) of human prolactin (Prl). Human purified Prl (NIAMDD-hPrl-16) was labelled with 125I by the Chloramine-T or alternatively by the lactoperoxidase method. As reference preparation we used Prl isolated from the ethanolic step of the routine procedure for the preparation of human growth hormone (hGH) for clinical purposes. The lactogenic receptors were prepared from the pregnant rabbit mammary gland previously stimulated with insulin, cortisone and dried thyroid extract. The final receptor preparations obtained by ultracentrifugation contained 8.85-39.36 mg protein per ml. The prolactin was measured in the human sera and in our hPrl preparations by a double antibody radioimmunoassay (RIA) system using the NIAMDD reagents. We developed a RRA system for hPrl using rabbit mammary receptor preparations with a protein concentration of about 4 mg/ml. The comparative competition showed the same magnitude of the inhibition of the tracer receptor binding of hPrl and hGH. This interference of hGH makes difficult the assessment of the specificity of the hPrl-RRA system otherwise accountable by the structural and/or biological relationship of the three lactogenic hormones: hPrl, hGH and human placental lactogen (hPL). Studies concerning the preparation of a purified and solubilized rabbit mammary receptor and of an antiserum for it are in progress in our laboratory with the objective to provide a useful tool for the investigation of the lactogenic receptor structure and function relationship.

Quantitative surface studies of protein adsorption by infrared spectroscopy. II. Quantification of adsorbed and bulk proteins

Attenuated total reflectance Fourier transform infrared spectra of surface-adsorbed proteins are correlated with concentration measurements determined by 125I-labeled proteins. This paper demonstrates that linear correlations between the intensity of the major bands of proteins and the quantity of proteins can be obtained for human albumin and immunoglobulin G up to surface concentrations of approximately 0.25 microgram/cm2. A poorer correlation was observed for human fibrinogen. A linear correlation was also observed between the concentration in the bulk solution and the major bands of albumin up to a concentration of 60 mg/ml.

The endosomal concentration of a mannose 6-phosphate receptor is unchanged in the absence of ligand synthesis

The cation-independent mannose-6-phosphate (Man-6-P) receptor is involved in the targeting of newly synthesized lysosomal hydrolases. To investigate the intracellular distribution of this receptor, a conjugate of lactoperoxidase coupled to asialoorosomucoid was used to catalyze its iodination within the endosomes of human hepatoma (HepG2) cells. The 215-kD, cation-independent Man-6-P receptor was iodinated by this procedure as shown by pentamannosyl-6-phosphate-Sepharose affinity chromatography and by immunoprecipitation of labeled cell extracts. The amount of this receptor detected in endosomes was found to be unchanged after inhibition of protein synthesis with cycloheximide. If the Man-6-P receptor accumulates in the Golgi apparatus in the absence of lysosomal hydrolase synthesis, it should have been correspondingly depleted from endosomes after a period of cycloheximide treatment, because these pools of receptor are in rapid equilibrium. Therefore, these data suggest that newly synthesized ligands are not required for the transport of the cation-independent Man-6-P receptor from the Golgi apparatus to endosomes.

Generation of oligomeric insulin receptor forms by intramolecular sulfhydryl-disulfide exchange. Involvement of masked sulfhydryl groups

Insulin receptors from rat liver membranes were labelled with a 125I-labelled photoreactive insulin analogue or by iodination using lactoperoxidase and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Under nonreducing conditions different receptor forms with Mr 400,000 (alpha 2 beta 2), 360,000 (alpha 2 beta beta'), 330,000 (alpha 2 beta' beta'), 320,000 (alpha 2 beta), 280,000 (alpha 2 beta'), 240,000 (alpha 2), 210,000 (alpha beta), 165,000 (alpha beta') and 115,000 (alpha) were detected. The subunit composition of these receptor forms was determined by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis in the absence and presence of dithioerythritol. During denaturation in sodium dodecyl sulfate in the absence of reductants, the Mr 400,000 receptor form (alpha 2 beta 2) was converted into the Mr 320,000 (alpha 2 beta) and Mr 240,000 (alpha 2) receptor form. This conversion was prevented either by N-ethylmaleimide, oxidants, or low pH. In contrast, alkylation of the receptor with N-ethylmaleimide under non-denaturing conditions did not prevent the appearance of intermediate-sized receptor forms. Furthermore, the inhibition of receptor cleavage by N-ethylmaleimide during denaturation was also observed when the amount of free sulfhydryl groups was reconstituted by the addition of an unlabelled and non-alkylated receptor sample to the alkylated and photoaffinity-labelled receptor. These results suggest, that the generation of different oligomeric receptor forms detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis is due at least in part to the cleavage of one or both beta-subunits from the insulin receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffuse cytoplasmic staining of retinal capillary endothelium

The distribution of several hemeprotein tracers in retinal capillaries of Wistar-Furth rats was studied by electron microscopic cytochemistry after incubation in 3,3'-diaminobenzidine. Diffuse cytoplasmic reaction product was frequently observed in the endothelial cells after intravenous injection of horseradish peroxidase (HRP) or lactoperoxidase (LP), or after perfusion of HRP. Occasionally, pericytes were also diffusely stained. In contrast, injection of microperoxidase, catalase, or hemoglobin did not cause diffuse staining. The diffuse staining was similar with HRP types II, VI, and VIII, and at concentrations of 2.5, 5, and 10 mg/100 g body weight. Despite the staining, the blood-retinal barrier remained intact. The findings indicate that HRP and LP are capable of causing diffuse nonspecific staining of retinal capillary endothelial cells, even at relatively low concentrations. Since these tracers are frequently used in studies of the blood-retinal barrier, the results of such studies should be interpreted with caution.

Structure, biosynthesis, and polymorphism of chicken MHC class II (B-L) antigens and associated molecules

Chicken MHC class II (B-L) antigens were immunoprecipitated by the monoclonal antibody TaP1 from inbred chicken splenic leukocytes and a lymphoblastoid B cell line (RP9), and were studied by two dimensional gel electrophoresis. B-L antigens are composed of one alpha and one beta chain that are noncovalently bound at the cell surface. In all haplotypes studied, a single acidic 34,000 dalton non-polymorphic chain was observed, whereas two polymorphic chains could be distinguished, differing in both pH and m.w. The alpha-beta heterodimer is associated during its maturation in the cytoplasm with several basic invariant molecules with m.w. ranging from 30,000 to 42,000 daltons. Treatment of cells with tunicamycin and treatment of immunoprecipitated molecules with several glycosidases revealed a complex process of maturation for all of these molecules. The alpha and beta chains undergo a N-glycosylation of complex type, whereas the invariant molecules bear N-linked high mannose glycans, and perhaps also O-linked glycans in the RP9 lymphoblastoid line. Overall, the B-L antigens appear very similar to the HLA-DR and I-E antigens.

Reduction of lactoperoxidase by the dithionite anion monomer

The reduction of lactoperoxidase with sodium dithionite has been studied by means of stopped-flow spectrophotometry in an anaerobic system. Under pseudo-first-order conditions the rate constant was found to be linearly dependent on the square root of the dithionite concentration, which confirms the monomeric radical, SO2- as the reducing species. The second-order rate constant is moderately influenced by increased ionic strength but drastically increased at lower pH. The pH dependence supports the previously suggested existence of a carboxyl group, essential to the different enzymatic functions of lactoperoxidase. The second-order rate constant for the reduction of lactoperoxidase at pH 7.0 (kappa 1 = 1.3 X 10(5) M-1 s-1) was about three times higher than the rate constant for the reduction of cyanide-bound lactoperoxidase and two times the rate constant for the reduction of the fluoride-lactoperoxidase complex.

Lactoperoxidase consists of domains: a scanning calorimetric study

Thermal unfolding of lactoperoxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) was studied by means of differential scanning calorimetry and optical methods. The protein consists of at least two domains differing in thermostability. The prosthetic group belongs to the domain of lower thermostability. Thermodynamic parameters of protein unfolding are given and found to be similar to corresponding data for globular proteins.

Iodogen-catalysed iodination of human calcitonin and Tyr(0)-katacalcin and purification of their mono- and di-iodinated derivatives by chromatofocussing

Synthetic calcitonin (CT) and Tyr(0)-katacalcin (tKT) were radioiodinated with Iodogen to high specific activity and with high yields. The products of the iodination procedure were chromatographed on Sephadex G-25 to remove unreacted iodide and then separated by chromatofocussing on PBE 94 (pH 9.6-6.0 for CT and pH 7.4-4.0 for tKT). Clear separation between uniodinated peptides and their mono- and di-iodinated derivatives was achieved with specific activities of 1900 and 3800 Ci/mmol for the respective mono- and di-iodinated peptides. Yields were up to 36 and 24% of mono- and di-iodinated CT and 41 and 29% for mono- and di-iodinated tKT. Our results show that Iodogen provides an effective and gentle way to iodinate peptides with high efficiency. Chromatofocussing is a simple, inexpensive and instrumentally undemanding method that can be performed without specialized chromatographic equipment and that should be applicable to a variety of different tracer preparations.

Radioiodination of tyrosine residue(s) of ox testis and of wheat germ calmodulins

Radioiodination of the two tyrosine residues (Tyr-99 and Tyr-138) of ox testis calmodulin was performed using several methods, and studied through the specific activity, and the [125I]iodoamino acid analysis of the radiolabeled calmodulins. Hydrolysis by thrombin of 125I-calmodulin labeled by the lactoperoxidase method and subsequent isolation of peptides TM1 and TM2 by gel electrophoresis showed preferential labeling by 125I of Tyr-99 (TM1) over Tyr-138 (TM2). Analysis of [125I]iodoamino acids of radiolabeled TM1, TM2 and calmodulin demonstrated that [125I]monoiodotyrosine was predominant, the remainder being [125I]diiodotyrosine. Radioiodination of wheat germ calmodulin, which contains a single tyrosine residue (Tyr-139), showed that only TM2 was labeled by 125I on the Tyr-139 residue and also on the His-108 residue (radiolabeled monoiodotyrosine, diiodotyrosine and monoiodohistidine being present).

A detailed examination of the iodination of beta-galactosidase: stoichiometric inactivation by nonspecific iodination

The incorporation of 125I, using lactoperoxidase, and the subsequent inactivation of beta-galactosidase in the period when incorporation and inactivation were stoichiometric were investigated in detail. The high pressure liquid chromatographic (HPLC) radioactive profiles of the tryptic peptides of samples taken in the stoichiometric period showed that, although two labelled peptides predominated, there were other labelled peptides. The predominating peptides were shown to be the mono- and di-iodinated forms of the peptide containing Tyr-253. This confirmed the result of an earlier study, but quantitation showed that this iodination accounted for only 15-18% of the total. To show that the other labelled peptides in the HPLC profiles were not merely oxidized or partially digested forms of the peptide containing Tyr-253, two experiments were carried out. In one of the experiments, two of the other labelled peptides were isolated and identified as iodinated forms of the peptide containing Tyr-285 (5-7% of the incorporation). In the other experiment, four additional labelled fractions from the HPLC eluate were treated further with trypsin. No further digestion was observed and thus these peptides did not result from incomplete digestion of the sequence containing Tyr-253. Overall, these results show that, although the incorporation of 125I was stoichiometric with inactivation, no single Tyr was responsible for the inactivation as was tentatively suggested previously. The competitive inhibitor isopropyl-beta-D-thiogalactopyranoside (IPTG) was effective in reducing the rates of inactivation of the enzyme and incorporation of 125I, but the same peptides were labelled in the presence of IPTG as in its absence.

Evidence for and partial characterization of three major and three minor chromatographic forms of human neutrophil myeloperoxidase

Myeloperoxidase (MPO) is an enzyme found in the azurophil granules of neutrophils. Cation-exchange chromatography on carboxymethyl-cellulose previously has been used to demonstrate the heterogeneity of the peroxidase enzymes isolated from human neutrophils. In this study, fast protein liquid chromatography (FPLC) was used to separate and purify three major (I, II, and III) and three minor (IIa, IIIa, IIIb) forms of MPO from isolated neutrophil granules. Purity was confirmed by polyacrylamide gel electrophoresis in the presence of cetyltrimethylammonium bromide (CETAB-PAGE), by crossed immunoelectrophoresis, and by spectral characteristics. All three major forms were indistinguishable by immunodiffusion against rabbit antiserum, scanning spectrophotometry, and amino acid composition. They differed in their elution from a cation-exchange resin, inhibition by 3-amino-1,2,4-triazole, migration rate in CETAB-PAGE, and subunit molecular weight. Subunit molecular weight was examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). All three major forms appeared to consist of heavy (H), intermediate (M), and light (L) peptides. The M peptide appeared to be derived from the H subunit. All L subunits exhibited a molecular weight of 14,500. The molecular weights for the H subunits varied, and were 60,000, 59,000, and 57,000 for MPO I, II, and III, respectively. The molecular weights for the M peptides were 44,100, 43,000, and 42,000 for MPO I, II, and III, respectively. The treatment of neutrophils, granules, and extracts with protease inhibitors and sodium azide did not block the appearance of three major forms of MPO. Thus, neither protease activity nor MPO autooxidation during extraction and purification procedures is responsible for the appearance of multiple chromatographic forms of MPO derived from human neutrophils.

Identification of the macrophage mannose receptor as a 175-kDa membrane protein

Mannose-lactoperoxidase, a neoglycoprotein prepared by reaction of lactoperoxidase with cyanomethyl 1-thiomannoside, bound to alveolar macrophages at 4 degrees C (Kd = 5.8 X 10(-8) M) and was rapidly internalized at 37 degrees C (K uptake = 2 X 10(-8) M). Mannose-lactoperoxidase binding and uptake were blocked by yeast mannan, and mannose-lactoperoxidase inhibited uptake of 125I-labeled mannose-BSA (bovine serum albumin). Radioiodination of cells with surface-bound mannose-lactoperoxidase was carried out in the presence of glucose and glucose oxidase. A major polypeptide (175 kDa) was radioiodinated by this procedure. Iodination of the 175-kDa polypeptide appeared to be receptor-mediated, since it was blocked by the presence of yeast mannan. Specific iodination was absent from receptor-negative cells. To demonstrate that the 175-kDa species is a ligand-binding protein, cells were iodinated by the standard lactoperoxidase method. Washed cells were then allowed to bind mannose-BSA. Receptor-ligand complexes, prepared by detergent extraction, were passed over anti-BSA IgG affinity columns. Mannose, but not mannose 6-phosphate or galactose, eluted a radioactive protein from the column that migrated with an apparent molecular mass of 175 kDa on NaDodSO4/PAGE. Detergent extracts of crude membranes prepared from macrophage-enriched whole rabbit lung were adsorbed to mannose-Sepharose; the fraction obtained by elution with mannose contained two protein components of 175 and 55 kDa. Subsequent chromatography on N-acetylglucosamine-agarose yielded a single protein of 175 kDa. The 175-kDa polypeptide was shown to bind 125I-labeled mannose-BSA in a precipitation assay. This binding could be blocked with mannan or mannose-BSA. The results indicate that the cell-surface mannose receptor is a 175-kDa protein.

Pathways of endocytosis in cultured macrophages. Electron microscopic autoradiographic tracing of iodinated plasma membrane proteins

Lactoperoxidase-mediated iodination at 4 degrees C--an established method for covalent labelling of plasma membrane proteins--and quantitative electron microscopic autoradiography were used to follow the pathways of endocytosis in mouse macrophages in vitro. Directly after the labelling, the autoradiographic grains were concentrated to the cell surface. After warming to 37 degrees C, radioactive material was rapidly internalized into cytoplasmic vesicles and subsequently transferred to lysosomes as well as to the Golgi complex. Maximum grain density (% grains/% volume) over the vesicles was observed after 15 min, over the lysosomes after 30 to 45 min and over the Golgi complex after 30 and 90 min. Throughout the experimental period (120 min), the vesicles showed the largest fraction of intracellular grains, but higher grain densities occurred in lysosomes as well as in stacked Golgi cisternae and Golgi-associated vesicles. In spite of the internalization process, the labelling of the cell surface came to a steady state already after 30 min and at all intervals more than 50% of the autoradiographic grains were localized to this compartment. About 25% of the cell-associated radioactivity was lost rapidly with a half-life of 20 to 25 min and the remaining 75% slowly with a half-life of 7 to 9 h. The results indicate that membrane internalized by endocytosis partly follows a route to the lysosomes and that, additionally, there exists a route to and through the Golgi complex. They further support earlier notions of a bidirectional traffic between the surface and interior of the cell and suggest that recycling of membrane components may take place from endocytic vesicles, lysosomes, as well as the Golgi complex.

A unique polypeptide on avian antigen-specific suppressor T-cell radioiodinated in situ by antigen-lactoperoxidase conjugates

Antigen-specific receptors of B- or T-cells were selectively radiolabeled among the spleen cells from either human gammaglobulin immunized normal or bursectomized agammaglobulinemic chickens. Selective in situ radioiodination was accomplished by employing lactoperoxidase (LPO) covalently linked to antigen (Ag). Ag-specific receptors on B- or T-cells were allowed to bind Ag-LPO conjugates via the Ag portion of the conjugates and then to be selectively catalyzed for iodination by the LPO portion of the bound Ag-LPO conjugates. Radioiodinated cells were either processed for autoradiography to detect Ag-binding cells directly under the microscope or solubilized with detergents for protein analysis with two-dimensional (2-D) gel electrophoresis. On a cellular level, Ag-binding B- and T-cells were selectively radiolabeled and clearly visualized via autoradiography. On a molecular level, selectively radiolabeled Ag-specific membrane immunoglobulin of B-cells was demonstrated on 2-D gel autoradiographs. Furthermore, a unique polypeptide of Ag-specific T-cells with a reduced apparent mol. wt of 27 K and an apparent pI of 5.5-5.7 was demonstrated on 2-D gel autoradiograms. The 27 K molecule appears to be a T-cell receptor component itself, or a closely associated molecule.