Studies on the inhibition of sialyl- and galactosyltransferases

The inhibition of the alpha-2,6-sialyltransferase from rat liver, the alpha-2,3-sialyltransferase from porcine submandibular gland and of the galactosyltransferase from human milk were studied using monosaccharide-, nucleoside- and nucleotide-derivatives of their naturally occurring donor substrates cytidine 5'-monophosphate-N-acetylneuraminic acid and uridine 5'-diphosphate-galactose, respectively. Only the corresponding nucleosides/nucleotides showed inhibitory activity. Periodate oxidation of CMP or CMP-Neu5Ac and of UMP or UDP-Gal led to reduced inhibitory efficiency with the respective transferase. The type and reversibility of the inhibition of some of these compounds, as well as the corresponding Ki values were determined.

Establishment of monoclonal antibodies against carbohydrate moiety of gastric mucins distributed in the different sites and layers of rat gastric mucosa

Eight monoclonal antibodies (MAbs), designated RGM21 approximately RGM42, were generated against mucin purified from the rat gastric mucosa. By applying ELISA, all of these MAbs were proved to react not only with the purified mucin, but also with the oligosaccharide mixture obtained from the antigenic mucin by alkaline borohydride treatment. Treatment of the mucin-attached ELISA well with trypsin, sodium periodate or galactose oxidase prior to the addition of the MAb was applied to characterize these MAbs. Histochemical observation indicated that all these MAbs were able to stain the formalin fixed-paraffin embedded sections of the rat gastroduodenal mucosa. Although each of these MAbs reacted with distinct mucus-producing cells localized in particular regions of the gastroduodenal mucosa, their staining specificity could generally be classified into four groups. These MAbs might be useful for estimating the physiological and pathological changes of mucins in the gastric mucosa.

Synthesis of 6-deoxy-5-thio-D-glucose

Three routes were investigated for the conversion of D-glucose into the title compound. In the first approach, reduction of the 5,6-thiirane ring of 5,6-dideoxy-5, 6-epithio-1,2-O-isopropylidene-alpha-D-glucofuranose (17) as well as that of its 3-O-allyl derivative (13) with lithium aluminium hydride was investigated; 17 afforded the corresponding 6-deoxy derivative besides di-, tri-, and poly-mers, whereas only polymers were formed from 13. In the second approach, the oxirane ring of 3-O-allyl-5,6-anhydro-1,2-O-isopropylidene-beta-L-idofuranose was reduced by sodium borohydride and the resulting 6-deoxy derivative was converted into the 5-thiobenzoate; the corresponding hex-4-enofuranose was formed as a byproduct. In the third approach partial mesylation of methyl 5-thio-alpha-D-glucopyranoside was attempted, but the 6-mesylate 27 could be isolated only in modest yield (28%) together with rearranged 2,5-thioanhydromannofuranoside derivatives. The mechanism of this rearrangement is discussed in detail. The 6-mesylate 27 was converted via the 6-iodo derivative into the title compound.

Liposomal formulations containing sodium mercaptoundecahydrododecaborate (BSH) for boron neutron capture therapy

Sodium mercaptoundecahydrododecaborate or BSH is a compound most widely used for boron neutron capture therapy (BNCT). Liposome formulations containing BSH, with or without steric stabilization, were prepared as potential agents for delivery of boron compounds for BNCT. Liposomes composed of DPPC/CHOL in a molar ratio 1:1 (PEG concentration: 5 mol%) were prepared having an average diameter in the range of 100-110 nm 200 mu L of liposomes (l.88 mg phospholipid/mouse and 3.5-5.8 mg BSH/kg body weight) were injected in mice via the tail vein. Both types of liposomes resulted in a significant improvement in the circulation time of BSH compared to that obtained previously after injecting free BSH. The mean percent injected BSH remaining in circulation at the end of 24 h was 19% for the PEG-liposomes compared to the corresponding value of 7% for the conventional liposomes. The mean percent uptake by the liver and spleen was not significantly different for the two types of liposomes; the blood/RES ratios were higher for the PEG-liposomes at all time points indicating that a higher fraction of injected BSH was available in circulation. The PEG-liposomes could be further explored as a means of enhance boron drug delivery to tumor cells for BNCT.

Isolation of heparin-derived oligosaccharides containing 2-O-sulfated hexuronic acids, by lipoprotein lipase affinity chromatography

Oligosaccharides (hexa to dodeca) terminating with [3H]2,5-anhydromannitol (AManR) were isolated from heparin by partial cleavage with nitrous acid at low pH (pH 1.5) followed by gel filtration and reduction with [3H]NaBH4. They were subsequently chromatographed on a lipoprotein lipase (LpL)-Sepharose column. High- and low-affinity oligosaccharides for LpL were isolated and characterized. Disaccharide analysis revealed the presence of (IdceA(2-SO4)-->AManR6-SO4) and (IdceA(2-SO4)-->AManR) as the major disaccharide products after low pH nitrous acid treatment. The oligosaccharides are, therefore, enriched in IdceA(2-SO4)-(GlcNSO4 +/- 6-SO4) sequences. Furthermore, they are found to be composed of 2-O-sulfated hexuronic acid-containing sequences, structural features, characteristic of heparin and heparan sulfate oligosaccharides with potential antiproliferative activities. These oligosaccharides may have the potential as lipase-releasing agents from endothelial and adipocyte surfaces.

The chemical structure of amylose and amylopectin fractions of starch from tobacco leaves during development and diurnally-nocturnally

Starches, isolated from rapidly expanding tobacco leaves four times during the day and night and once from fully expanded leaves, were fractionated with concanavalin A. From an examination of the amounts and properties of amylose, the diurnal decrease in iodine absorption of the starches on illumination appeared to be due to an increase in its branched character, and possibly the presence of unbranched polymer of low dp, combined with a decrease in the proportion of amylose fraction. The increase in apparent amylose content with age was due to an increase in the proportion of amylose. The amylose fractions at different times had only small differences in average mol size in solution and relative mol wt (M(r) near 4 x 10(5)) which were lower than those of storage organs. The average mol size in solution and relative mol wt of the amylopectins decreased during illumination, increased in darkness, and were lower (M(r) 2-2.7 x 10(6)) at all times than those from storage organs. Debranching followed by size-exclusion chromatography [on Fractogel TSK 50(S)] gave similar proportions of long, medium, and short chains for all amylopectin samples, and these proportions differed from those for debranched amylopectin from n-maize seed starch. On debranching and chromatography of the amylopectin beta-limit dextrins (which gives an estimate of the proportions of core chains) differences persisted. Structural characteristics of amylopectin from tobacco leaf starch were similar to those of normal genotypes from storage organs. The proportion of glucosyl units in core chains, the external-to-core chain ratio, and indices of compactness were calculated for a number of (1-->4)(1-->6) alpha-glucans. A plot of the index of compactness for glycogens and amylopectins showed that the decrease in compactness and the increase in total average chain length that occurs from glycogen to normal and then to amylose extender amylopectins involves a proportionate increase in average internal, external, and core chain lengths and not a selective increase in one type of chain.

A lysine to arginine substitution at position 146 of rabbit aldolase A changes the rate-determining step to Schiff base formation

Lys146 of rabbit aldolase A [D-fructose-1,6-bis(phosphate): D-glyceraldehyde-3-phosphate lyase, EC 4.1.2.13] was changed to arginine by site-directed mutagenesis. The kcat of the resulting mutant protein, K146R, was 500 times slower than wild-type in steady-state kinetic assays for both cleavage and condensation of fructose-1,6-bis(phosphate), while the K(m) for this substrate was unchanged. Analysis of the rate of formation of catalytic intermediates showed K146R was significantly different from the wild-type enzyme and other enzymes mutated at this site. Single-turnover experiments using acid precipitation to trap the Schiff base intermediate on the wild-type enzyme failed to show a build-up of this intermediate on K146R. However, K146R retained the ability to form the Schiff base intermediate as shown by the significant amounts of Schiff base intermediate trapped with NaBH4. In the single-turnover experiments it appeared that the Schiff base intermediate was converted to products more rapidly than it was produced. This suggested a maximal rate of Schiff base formation of 0.022 s-1, which was close to the value of kcat for this enzyme. This observation is strikingly different from the wild-type enzyme in which Schiff base formation is > 100 times faster than kcat. For K146R it appears that steps up to and including Schiff base formation are rate limiting for the catalytic reaction. The carbanion intermediate derived from either substrate or product, and the equilibrium concentrations of covalent enzyme-substrate intermediates, were much lower on K146R than on the wild-type enzyme. The greater bulk of the guanidino moiety may destabilize the covalent enzyme-substrate intermediates, thereby slowing the rate of Schiff base formation such that it becomes rate limiting. The K146R mutant enzyme is significantly more active than other enzymes mutated at this site, perhaps because it maintains a positively charged group at an essential position in the active site or perhaps the Arg functionally substitutes as a general acid/base catalyst in both Schiff base formation and in subsequent abstraction of the C4-hydroxyl proton.

Oxidative inactivation of tyrosine hydroxylase in substantia nigra of aged rat

Study of the tyrosine hydroxylase enzyme from substantia nigra and striatum during the aging period of the rat has discovered a significant decrease (55%) of TH activity in substantia nigra between 12 and 24 mo of age. The amount of TH in substantia nigra also decreased (30%) during aging. This loss in TH activity of substantia nigra appears to be produced by the decrease in TH content along with an inactivation process. Our finding showed a significant increase of carbonyl groups in the proteins of rat substantia nigra with aging. A statistically significant increase of carbonyl groups in TH enzyme was found in aged rat brain substantia nigra, indicating that oxidative damage could be the inactivation process that explains the decrease in TH activity found during aging. This hypothesis was corroborated by the fact that when rat striatal homogenate was incubated with hydrogen peroxide, there was a time-dependent decrease in TH activity, which highly correlated with measurements of carbonyl groups content of TH enzyme. The importance of these results may be in their relationship, considering that substantia nigra is preferentially affected in many neurodegenerative disorders.

Interspecies pharmacokinetic scaling of BSH in mice, rats, rabbits, and humans

Sodium mercaptoundecahydrododecaborate or BSH is an important compound for boron neutron capture therapy (BNCT). The total clearance and steady state volume of distribution of BSH in humans and in laboratory animals were analyzed as a function of species body weight using the allometric equation for interspecies scaling. Significant linear relationships were obtained between log CLt (Lh-1) and log W (kg) (r = 0.972; p = 0.028) as well as log VSS (L) and log W (kg) (r = 0.999; p = 0.0005). The corresponding allometric equations were CLt = 0.127 W0.68 and VSS = 1.557 W0.87, respectively. BSH clearance in various species was shown to be a constant fraction (0.26) of creatinine clearance, the relationship being independent of body weight. Thus BSH clearance in various species occurred at similar pace when measured by a physiological parameter (creatinine clearance) rather than chronological time. Interspecies scale-up of plasma concentration-time data for the four species using a complex Dedrick plot resulted in similar profiles. Our results indicate that the BSH data obtained in laboratory animals could be utilized to generate preliminary estimates of the pharmacokinetic parameters in humans. These parameters can serve as guidelines for better planning of clinical studies.

Essential lysine residue in glutathione reductase: chemical modification by pyridoxal 5'-phosphate

Yeast glutathione reductase was inactivated by pyridoxal 5'-phosphate. The inhibition was reversed by dilution. The enzyme-pyridoxal 5'-phosphate complex on reduction with sodium borohydride gave a characteristic absorption maximum at 325 nm and fluorescence maximum at 395 nm when exciated at 325 nm. These results were consistent with the reaction of epsilon-amino group of lysine residue of the enzyme with pyridoxal 5'-phosphate. The enzyme was protected against pyridoxal 5'-phosphate inhibition by NADP indicating thereby that the essential lysine residues are present during the NADP binding site.

The in vitro effect of sodium mercaptoundecahydrododecaborate (borocaptate) on sulfhydryl groups of different rat tissues

The effect of borocaptate on structural protein sulfhydryl (SH) groups of different organs and kidney subcellular fractions was studied in vitro. It was shown that the binding capacity of borocaptate is not the same for different tissues and subcellular fractions. The highest binding capacity was in the liver, while kidney and brain values were significantly lower. Therefore, it appears that the same concentration of borocaptate may have different effects in various organs.

Subcellular boron-10 localization in glioblastoma for boron neutron capture therapy with Na2B12H11SH

Because of the short range of the highly energetic particles helium-4 and lithium-7 that results from neutron-induced disintegration of boron-10, the efficacy of Boron Neutron Capture Therapy (BNCT) is heavily dependent on 10B-microlocation. Despite the crucial importance of boron-10, there is little specific information with regard to the agent currently used for inducing BNCT, namely Na2B12H11SH. In the present study, a subcellular 10B-location was investigated in tumor tissue obtained from seven patients with glioblastoma World Health Organization Grade IV. These patients received Na2B12H11SH at doses used in therapeutic trials (75 mg/kg body weight in five patients, and 150 mg/kg body weight in two patients, respectively). In three cases, boron-10 was identified in glioblastoma cells by laser microprobe mass analysis. In these tumors, boron-10 was found only in the nuclei of neoplastic cells but not in other cell compartments. These preliminary results suggest a predominant association of Na2B12H11SH with the nuclei of malignant glioma cells and thus support the value of Na2B12H11SH as a suitable boron carrier for BNCT.

Topology of CNS myelin proteolipid protein: evidence for the nonenzymatic glycosylation of extracytoplasmic domains in normal and diabetic animals

Myelin proteolipid protein (PLP), the main integral membrane protein in the central nervous system myelin, was labeled at the extracytoplasmic domains with the membrane impermeant reagents pyridoxal 5'-phosphate and tritiated borohydride. Lysine-217, located in the fourth hydrophilic domain of PLP, was found to be the major labeled residue, which defined this domain to be extracytoplasmic in agreement with our previously proposed topological model. The remarkably high reactivity in vitro of this residue as compared to all other lysines in PLP led us to investigate the possible modification of PLP in vivo by other carbonyl compounds. We demonstrate that PLP is the most highly nonenzymatically glycosylated membrane protein in murine and bovine brain. The degree of modification increases significantly under hyperglycemic conditions, as studied in diabetic mice. The majority of the glycosylation sites are also located at extracytoplasmic domains. The degree of nonenzymatic glycosylation of PLP may be related to late diabetic complications affecting the central nervous system.

Thiobarbiturate and fructosamine assays: significance and interest of the borohydride blank

The acute-phase reaction (APR) induces the production by the liver of short-lived glycoproteins. The carbohydrate moiety of these proteins is thought to interfere with the thiobarbiturate (TBA) and nitroblue tetrazolium colorimetric tests which are used for assaying non-enzymatic glycosylation (NEG) of serum proteins. The aim of the present study was to assess the effect of the APR on the specificity of the colorimetric tests in non-diabetic and diabetic subjects. A positive correlation was found between C-reactive protein (CRP), an APR glycoprotein, and non-specific TBA reactivity as determined after borohydride reduction (BH4-resistant TBA, BR-TBA), both in non-diabetics (r = 0.61; P < 0.01) and diabetics (r = 0.68; P < 0.01). The BH4-sensitive specific TBA (SP-TBA) was not influenced by glycoproteins, and its increase in diabetics was correlated with the nitroblue tetrazolium assay (r = 0.89; P < 0.01). An independent effect of diabetes and APR on non-specific TBA was also demonstrated, suggesting an effect of hyperglycaemia on both protein glycation and glycosylation. TBA with borohydride reduction is an attractive tool for the study of complex glycoproteins in diabetes.

Identification of the palmitoylation site in rat myelin P0 glycoprotein

P0 glycoprotein, the major protein of PNS myelin, contains approximately 1 mol of covalently bound long-chain fatty acids. To determine the chemical nature of the fatty acid-protein linkage, P0 was labeled in rat sciatic nerve slices with [3H]palmitic acid and subsequently treated with various reagents. The protein-bound palmitate was released by incubation with the reducing agents dithiothreitol and 2-mercaptoethanol, and with 1 M hydroxylamine at pH 7.5. In addition, P0 was deacylated by treatment with 10 mM NaBH4 with the concomitant production of [3H]hexadecanol, indicating that the fatty acid is bound in a thioester linkage. This conclusion was supported further by the fact that deacylation with hydroxylamine generated free thiol groups, which were titrated with [14C]-iodoacetamide. To identify the cysteine residue involved in the thioester linkage, [14C]carboxyamidomethylated P0 was digested with trypsin and the resulting peptides analyzed by reversed-phase HPLC. Identification of the radioactive protein fragments by amino acid analysis and amino-terminal peptide sequencing revealed that Cys153 in rat P0 glycoprotein is the acylation site. The acylated cysteine is located at the junction of the putative transmembrane and cytoplasmic domains. This residue is also present in the P0 glycoprotein of other species, including human, bovine, mice, and chicken.

Affinity-labeling of an NADPH-binding site on the heavy subunit of flavocytochrome b558 in particulate NADPH oxidase from activated human neutrophils

Cell stimulation of blood phagocytes activates the superoxide-producing NADPH oxidase. Cytochrome b558, one of the two oxidase redox components, comprises a light (alpha) and a heavy glycosylated (beta) subunit. The other redox component, a flavoprotein, is now thought to be the heavy subunit, on the basis of amino acid sequence comparisons and of reconstitution experiments with purified components. We published that pyridoxal-5'-diphospho-5'-adenosine is an inactivating affinity label for the NADPH-binding site of particulate oxidase from activated neutrophils. We have now radiolabeled the inactivated oxidase by reducing with Na[3H]BH4 the Schiff base formed between proteins and the reagent. Upon SDS-PAGE, the NADPH-inhibitable incorporation is found at the same position as the immunodetectable cytochrome heavy subunit, before and after deglycosylation. Membranes from either activated cells of a cytochrome-deficient X-linked granulomatous disease patient or normal resting cells show no incorporation at this position. Our results provide experimental evidence for the existence on the cytochrome b558 heavy chain of an NADPH-binding site which can only be affinity-labeled by PLP-AMP when the oxidase is active. This suggests the occurrence of a conformational change in the cofactor binding site upon enzyme activation.

Differentially expressed patterns of glycosaminoglycan structure in heparan sulfate proteoglycans and free chains

The metabolic relationships between heparan sulfate proteoglycans, free chains, and oligosaccharides in different cell locations were evaluated by comparing their glycosaminoglycan structure. Metabolically labeled heparan sulfate proteoglycans of BALB/c 3T3 cell layers and in conditioned medium were compared with the heparan sulfate free chains (modal mass = 10 kDa) and oligosaccharides (modal mass = 3 kDa) of the cells. Nonlytic, in situ digestion with heparitinase I indicated that 90% of proteoglycans, 70% of the free chains, and 20% of the oligosaccharides were enzyme accessible, but there was no evidence using competitive ligands for binding of the products to the cell surface via the glycosaminoglycan moieties. Structurally, the membrane proteoglycans were the most O-/N-sulfated and yielded more tri- and tetra-sulfated di- and tetra-saccharides by nitrous acid degradation. In contrast, the side chains of medium proteoglycans were less sulfated and more polydisperse in mass, suggesting that most medium proteoglycans are not processed from membrane precursors. The heparan sulfate free chains were of lower mass, less sulfated, and more heterogeneous in distribution of the anionic groups than were proteoglycan side chains. Corroborating analytical heparitinase I digestion indicated that generation of di- and tetra-saccharides proportionately increased from membrane proteoglycan, to cell free chain, to medium proteoglycan categories. Because the structural patterns of the heparan sulfate free chains did not reveal a clear relationship with the side chains of the major proteoglycans, their origin was further probed by [3H]BH4-labeling of the reducing terminus under varying stringencies. The end-labeled residues obtained by nitrous or strong acid hydrolysis of the free chains showed insignificant amounts of galactose and xylose, but rather glucosamine N-sulfate and a residue likely generated from glucuronate. The effective labeling that was achieved with weak alkali indicated that covalent oligopeptide is not present. In summary, the heparan sulfate free chains, which in part are components of the cell surface, are of relatively low mass, are unassociated with covalent peptide, and most probably have a disaccharide motif of glucosamine N-sulfate and a uronate residue at the reducing end. Taken together, these observations suggest that the free chains originate by processing of precursor heparan sulfate proteoglycans on the cell surface via an endoglycosidase acting on an N-sulfated portion of the original polymer.

Intracellular distribution of various boron compounds for use in boron neutron capture therapy

The neutron capture reaction in boron (10B(n, alpha)7Li) generates two short-range particles with high linear energy transfer. The effect of neutron capture therapy depends on the selective localization of 10B atoms in target cells. The determination of the distribution of boron compounds in cancer cells at the subcellular level is required for the understanding of the effect of this treatment. The monomeric sulfhydryl borane (BSH) compound has been used clinically in Japan and preclinically in the U.S.A. Recently, new compounds have been developed: a dimeric sulfhydryl borane (BSSB), a boronophenylalanine (BPA), and two porphyrin complexes (BOPP and VCDP). This study demonstrates that the porphyrin complexes (BOPP and VCDP) are more cytotoxic than the other three compounds to the rat 9L gliosarcoma cell line. Using atomic absorption spectrophotometry to determine boron content for cellular uptake studies of these agents, we found that of the five compounds tested BOPP (25 microM) exposure resulted in the greatest boron uptake averaging 305 ng B/10(6) cells. BSSB (500 microM) was second averaging 93 ng B/10(6) cells, BSH (500 microM) third averaging 62 ng B/10(6) cells, VCDP (25 microM) fourth averaging 58 ng B/10(6) cells, and BPA (500 microM) fifth averaging 7.4 ng B/10(6) cells. Data on the distribution of boron in the nuclei, mitochondria, lysosomes, microsomes, and cytosomes of 9L cells are also presented.

Accumulation of boron-10 (10B) in cell cultures exposed to mercaptododecaborate (Na2H(11)10B12SH) used for the neutron capture therapy of brain tumors

Toxicity of mercaptoundecahydro-closo-dodecaborate (MHB, Na2H(11)10B12SH) and accumulation of MHB-derived 10B were studied in E7 neuroblastoma, C6 glioma, HeLa cells and embryonic lung LEP 19 fibroblasts in culture in exponential and stationary phases of growth (2- and 7-day-old cultures, respectively). The pilot study of acute toxicity, performed on C6 glioma cells, showed good tolerance of the drug up to 1000 micrograms/ml (4.8 x 10(-3) M), when cell growth slowed and a small part of the population was lethally damaged (8.3%, 20-h incubation interval). The changes became more extensive and appeared sooner (toward 5 h) at 2000 micrograms MHB/ml (9.5 x 10(-3) M). None of the four cell lines used was found to be affected in gross morphology or growth by 200 micrograms MHB/ml within a 5-day culture interval. When exposed to this dose for 4 h, the amount of 10B accumulated in cell lines at the exponential growth phase ranged from 0.51 to 4.4 ng/micrograms protein; in the stationary cultures of the corresponding cell phenotype, the 10B values were 3 to 10 times lower (0.12-1.2 ng/micrograms protein). Irrespective of the growth phase, the values achieved in C6 glioma cells were several times higher than in the other cell lines. Furthermore, in the glioma cells, particularly in the exponential phase of growth, accumulation of 10B proceeded against the marked concentration gradient. The data provide a new indication for the use of MHB for boron neutron capture therapy of brain tumors.

Deletion of C-terminal 12 amino acids of GLUT1 protein does not abolish the transport activity

We engineered the GLUT1 cDNA to delete C-terminal 12 amino acids of encoded GLUT1 protein. This mutated GLUT1 protein expressed in CHO cells by transfection of its cDNA was demonstrated to reside on the plasma membrane by cell surface labeling technique, and retain the transport activity, similar to that of the wild-type GLUT1. In addition, metabolic labeling of the intact cells with 35S indicated that the half-life of the mutated GLUT1 was not significantly different from that of the wild-type GLUT1. These results suggest that C-terminal 12 amino acids of GLUT1 are not important for the transport activity and the stability of the protein. Taken together with our previous results on the mutant without C-terminal 37 amino acids, the amino acids between the 37th and the 13th from the C-terminus appear to be essential for the transport activity.

Fluorescence characteristics of peroxidation products in porcine intestinal brush-border membranes

Treatment of the porcine intestinal brush-border membranes with 100 microM ascorbic acid and 10 microM Fe2+ in the presence of various concentrations of tert-butyl hydroperoxide (t-BuOOH) resulted in a marked fluorescence development at 430 nm, depending on the hydroperoxide concentration. This fluorescence formation was closely related to lipid peroxidation of the membranes as assessed by formation of conjugated diene. However there is no linear relation between thiobarbituric acid-reactive substances (TBARS) and fluorescence formation. On the other hand, fluorescence formation in the membranes by treatment with ascorbic acid/Fe2+ or t-BuOOH alone was negligible. The results with antioxidants and radical scavengers suggest that ascorbic acid/Fe2+/t-BuOOH-induced lipid peroxidation of the membranes is mainly due to t-butoxyl and/or t-butyl peroxy radicals. Most TBARS produced during the peroxidation reaction were released from the membranes, but fluorescent products remained in the membrane components. The fluorescence properties of products formed by lipid peroxidation of the membranes were compared with those of products derived from the interaction of malondialdehyde (MDA) or acetaldehyde with the membranes. The fluorescence products in the acetaldehyde-modified membranes also exhibited the emission maximum at 430 nm, while the emission maximum of MDA-modified membranes was 470 nm. The fluorescence intensity of MDA-modified membranes was markedly decreased by treatment with 10 mM NaBH4 but that of the peroxidized or acetaldehyde-modified membranes was enhanced by about two-fold with the treatment. In addition, a pH dependence profile revealed that the fluorescence intensity of the peroxidized or acetaldehyde-modified membranes decreases with increasing pH of the medium, whereas that of MDA-modified ones did not change over the pH range from 5.4 to 8.0. On the basis of these results, the fluorescence properties of products formed in the intestinal brush-border membranes by lipid peroxidation are discussed.

The influence of aminoguanidine on borohydride reducible collagen cross-links and wound strength

The mechanical strength of skin wounds as well as the deposition of hydroxyproline and KB3H4 reducible hydroxylysinonorleucine (HLNL) and dihydroxylysinonorleucine (DHLNL) cross-links in subcutaneously implanted cellulose sponges have been investigated in rats treated with aminoguanidine (AG) or beta-aminopropionitrile (BAPN). Treatment with AG (25 mg/kg BW/day) did not influence the mechanical strength of the wounds, the deposition of hydroxyproline or the pattern of reducible collagen cross-links, whereas AG (125 mg/kg BW/day) reduced the maximum load by 17%, but did not influence the deposition of hydroxyproline or reducible cross-linking pattern. Treatment with BAPN (333 mg/kg BW/day) reduced the strength of the wounds by 59%, the HLNL by 50% and the DHLNL 57%, whereas the deposition of hydroxyproline did not seem to be influenced by BAPN treatment. In conclusion, AG at moderate dosage does not seem to influence the formation of lysyl oxidase dependent reducible cross-links of collagen.

Fluorescent and cross-linked proteins formed by free radical and aldehyde species generated during lipid oxidation

One of the mechanisms for the formation of lipofuscin-like fluorescent substances is considered to be related to lipid oxidation of tissues. Induction of lipid oxidation in tissues or cells produces cross-links and borohydride-reducible functions together with fluorescence in proteins. In order to elucidate the structures of fluorophores, cross-links and borohydride-reducible functions produced in proteins by lipid oxidation, the reactions of a lipid peroxy free radical with amino acids and proteins, and those of an aldehyde with primary amines were investigated. We demonstrated here two possible types of the reactions that produce the modified proteins. A peroxy free radical generated during lipid oxidation may attack the tyrosine residue in proteins to form the tyrosine radical which may be in turn dimerized into fluorescent and cross-linked tyrosine dimer. aldehyde species formed by degradation of the peroxy free radical may be polymerized into dimer, trimer, tetramer and so on, which may react with the amino groups of protein to produce fluorescence, cross-links and borohydride-reducible functions. Cross-links can be produced by the formation of Schiff base between the tetrameric dialdehyde and the amino groups of proteins.

Activation energy of sulfate ion transport across methylated human erythrocyte membranes

Activation energy EA of the sulfate ions transport process across human erythrocyte membranes modified by reductive methylation has been measured. It has been found that exhaustive reductive methylation (3 times) with formaldehyde and borohydride inhibits the sulfate-equilibrium exchange, by a maximum of about 40%. However, methylation has no measurable effect on activation energy, since the evaluated EA values for control and methylated cells remain the same within the experimental error range.

Inactivation of the Lactobacillus leichmannii ribonucleoside triphosphate reductase by 2'-chloro-2'-deoxyuridine 5'-triphosphate: stoichiometry of inactivation, site of inactivation, and mechanism of the protein chromophore formation

The ribonucleoside triphosphate reductase (RTPR) of Lactobacillus leichmannii is inactivated by the substrate analogue 2'-chloro-2'-deoxyuridine 5'-triphosphate (ClUTP). Inactivation is due to alkylation by 2-methylene-3(2H)-furanone, a decomposition product of the enzymic product 3'-keto-2'-deoxyuridine triphosphate. The former has been unambiguously identified as 2-[(ethylthio)methyl]-3(2H)-furanone, an ethanethiol trapped adduct, which is identical by 1H NMR spectroscopy with material synthesized chemically. Subsequent to rapid inactivation, a slow process occurs that results in formation of a new protein-associated chromophore absorbing maximally near 320 nm. The terminal stages of the inactivation have now been investigated in detail. The alkylation and inactivation stoichiometries were studied as a function of the ratio of ClUTP to enzyme. At high enzyme concentrations (0.1 mM), 1 equiv of [5'-3H]ClUTP resulted in 0.9 equiv of 3H bound to protein and 83% inactivation. The amount of labeling of RTPR increased with increasing ClUTP concentration up to the maximum of approximately 4 labels/RTPR, yet the degree of inactivation did not increase proportionally. This suggests that (1) RTPR may be inactivated by alkylation of a single site and (2) decomposition of 3'-keto-dUTP is not necessarily enzyme catalyzed. The formation of the new protein chromophore was also monitored during inactivation and found to reach its full extent upon the first alkylation. Thus, out of four alkylation sites, only one appears capable of undergoing the subsequent reaction to form the new chromophore. While chromophore formation was prevented by NaBH4 treatment, the chromophore itself is resistant to reduction.(ABSTRACT TRUNCATED AT 250 WORDS)