Calcium-induced localization of calcium-activated neutral proteinase on plasma membranes.

The location of calcium-activated neutral proteinase (CANP) was determined in human erythrocytes by crosslinking CANP to co-localizing proteins using a photolabeling bifunctional reagent, 4,4'-dithiobisphenylazide (DTBPA). The crosslinked products were selectively isolated by immunoprecipitation with a polyclonal anti-CANP antibody and analyzed by SDS-polyacrylamide gel electrophoresis after cleavage of the crosslinkage. In the calcium-free incubation medium the main proteins crosslinked with CANP were cytosolic proteins such as hemoglobin. In the presence of calcium ions, on the other hand, membrane skeletal proteins such as spectrin, band 4.1, 4.2 and 6 proteins as well as band 3 were crosslinked with CANP. Addition of calcium ionophore further increased the amount of crosslinked membrane proteins. These results suggest that in the absence of calcium ions CANP exists diffusely in the cytoplasm and is crosslinked with cytoplasmic hemoglobin nonspecifically while in the presence of calcium ions CANP associated with membrane where it is crosslinked specifically with the lining proteins. Thus it is demonstrated biochemically that the localization of CANP is dynamic depending on the presence of calcium ions.

Marked depletion of plasma 1,5-anhydroglucitol, a major polyol, in streptozocin-induced diabetes in rats and the effect of insulin treatment.

Plasma levels of 1,5-anhydroglucitol (1,5AG), a major polyol resembling glucose in structure, fell rapidly and dramatically in streptozocin (STZ)-treated rats. 1,5AG fell immediately after STZ injection, reaching a plasma level 6 h after administration of the drug that was one-third that in the plasma of control rats. Reduction of 1,5AG was independent of the profile of blood glucose induced by STZ. After intravenous injection of [14C]-1,5AG, its plasma half-life was determined to be between 120 and 180 min. After a phase of acute decrease, the reduction of 1,5AG became gradual, stopping within 6 days after treatment. However, in some cases, the drop in 1,5AG was partially reversible by insulin treatment. The extent to which 1,5AG fell did not strictly correspond to the dose of STZ. The particular organ(s) consuming or accumulating 1,5AG was not identified. However, aside from the large amount of 1,5AG in plasma and the small amount of 1,5AG in the urine, the liver appears to be a significant organ for metabolism of 1,5AG.

Reduction and recovery of plasma 1,5-anhydro-D-glucitol level in diabetes mellitus.

The plasma concentration of 1,5-anhydro-D-glucitol (AG) was measured in 135 newly diagnosed patients who were referred for oral glucose tolerance tests. AG concentrations in the nondiabetic patients indicated that the mean value of normal AG concentration was 21.8 micrograms/ml (SD = 5.9 micrograms/ml, range 9.6-38.8 micrograms/ml). This distribution of AG concentration was significantly different from that in patients with impaired glucose tolerance (IGT) (13.3 +/- 5.4 micrograms/ml) and definitely different from that in diabetic patients (2.1 +/- 1.8 micrograms/ml). In a standard glucagon test, it was suggested that the decrease of plasma AG was affected not only by glycemic control of the patients but also by pancreatic cell secretory activity. The reduction of AG concentration was more marked in IDDM patients than in NIDDM patients. In longitudinal studies, AG concentration was shown to be sensitive to glycemic control. However, its recovery showed a tendency toward much delay after the improvement of fasting blood glucose or HbA1 concentrations. On the other hand, AG concentration showed negligible diurnal change and no immediate change as a result of diet, oral glucose load, or acute shift of the insulin level in both normal and diabetic subjects.

Plasma 1,5-anhydro-D-glucitol as new clinical marker of glycemic control in NIDDM patients.

To elucidate the value of using plasma 1,5-anhydro-D-glucitol (AG) as a marker of glycemic control in diabetic patients, the relationship between the plasma concentration of AG and glucosuria was examined in 152 patients with non-insulin-dependent diabetes mellitus (NIDDM). After recovery from the deterioration of glycemic control in NIDDM patients had started, AG began to increase day by day. The recovery of plasma AG showed a constant linear increase curve when excellent glycemic control was attained. The ordinary daily recovery rate of plasma AG was estimated to be 0.3 microgram/ml, which was independent of body weight, sex, age, the difference in treatment, the duration of diabetes, or the level of plasma AG among NIDDM patients. This rate decreased according to the increase in urinary glucose. When we calculated the decrease rate of plasma AG (delta AG), assuming 0.3 microgram/day to be the maximum increase rate in a day, we found a high correlation between delta AG and urinary glucose at almost all AG levels except the normal range and observed that plasma AG (A) times urinary glucose (G) was relatively constant. The formula A x G = 16 is a simple equation for rough estimation of urinary glucose from the plasma AG concentration in a stable glycemic-controlled NIDDM patient, and we call it the A.G index. The plasma AG also correlated significantly with fasting plasma glucose (r = -.810) and glycosylated hemoglobin (r = -.856) in the same stable glycemic-controlled NIDDM patients. Based on these observations, we propose that plasma AG can serve as a new marker that may provide sensitive and analytical information about glycemic control.

Distribution of 1,5-anhydro-D-glucitol in normal, diabetic, and perfused rat bodies.

The concentration of 1,5-anhydro-D-glucitol (AG) was determined in various organs and tissues of normal rats and rats rendered diabetic with streptozocin, using an AG-assay method in which AG was extracted after acid hydrolysis of the whole tissues. The organs and tissues examined included skin, muscle, liver, and kidney. The plasma of control rats contained 3-12 micrograms/ml of AG. In these rats, all the organs examined also contained AG at concentrations not much lower than that in the corresponding plasma, except for adipose tissues and testis, which have relatively small water spaces; the latter two contained AG at relatively low concentrations. In contrast, both the plasma and various organs of the diabetic rats contained only trace amounts of AG. The whole body perfusion of control rats depleted AG from most of the organs, the exception being spleen, the circulation system of which is known to have a structure that is difficult wash by means of perfusion. These observations indicated that AG readily diffused into the inter- and intra-cellular water spaces from the circulation. Accordingly, the plasma membranes of the cells in these organs were suggested to be permeable to AG.

High concentration of glucitol in fetal serum and glucitol permeable cells.

We found that the glucitol concentration was extraordinarily high in bovine fetal serum, which is routinely used for cell culture in laboratories: it was as much as two orders of magnitude higher than that reported for human adult serum. We also confirmed that the serum glucitol concentration in new born babies was on average 5.5-fold higher than in the maternal serum. These observations raise the possibility that some tissue(s) demand extracellular glucitol during embryogenesis and this indicates that the cells in such tissues could be permeable to glucitol. Since the hepatic metabolism of glucitol had been reported, we investigated glucitol permeability and its metabolism in rat hepatoma cells, Reuber H-35. The cells rapidly incorporated glucitol but the mode of incorporation was unusual: the incorporation rate was still proportional to the ambient glucitol concentration at 100 mM. The major part of the incorporated glucitol underwent metabolic conversion to probably negatively charged metabolites. Active synthesis of glucitol was also observed in the same cells. The cells proliferated normally in medium containing glucitol instead of glucose. This observation may indicate that glucitol can substitute for glucose in the culture of H-35 cells.

Simple hydrazidation method for carboxymethyl groups on cross-linked dextran.

A novel method for the use of CM-Sephadex in affinity chromatography is described. This method involves a carbodiimide-mediated synthesis of a lactone derivative, which is subsequently hydrazinolyzed to CM-Sephadex hydrazide. More than 90% of the carboxyl groups was converted to the hydrazide form by this method without any discernible degradation of the Sephadex beads. The hydrazide beads were further converted to the axide form and coupled with D-arginine and D-phenylalanine derivatives. These Sephadex derivatives contained more than 0.5 mmol of each amino acid per g dry beads and were found to be effective and specific adsorbents for carboxypeptidase B. This CM-Sephadex hydrazide should be useful in affinity chromatography because the resulting specific adsorbents involve stable amide coupling linkages and retain the physical properties of their precursor, Sephadex, which are favorable for column operation.

Transport of 1,5-anhydro-D-glucitol across plasma membranes in rat hepatoma cells.

The transport of 1,5-anhydro-D-glucitol (AG) across plasma membranes was investigated in rat hepatoma cells, Reuber H-35. The AG uptake by the cells showed a concentration gradient dependency: the uptake was saturated within 40 s, which was less than one-third of the saturation time for 2-deoxy-D-glucose (DG) uptake. Furthermore, the Km value of the transport system for AG was higher than 100 mM. Though AG has a pyranoid structure resembling that of glucose, AG did not compete for cellular uptake with DG, D-glucose or 3-O-methyl-D-glucose, which are taken into cells through the glucose transporters. Conversely, the DG transport was not inhibited by AG at concentrations up to 50 mM. AG transport was hardly inhibited by 10 microM cytochalasin B, which strongly inhibits glucose transporters. In contrast, the AG transport was inhibited by 100 microM phloretin much more strongly than the DG transport when cells were preincubated with the inhibitor; the inhibition constant was 28.0 microM. The AG transport was not inhibited by 100 microM phloridzin, while the DG uptake was slightly inhibited by phloridzin. On the basis of these observations we propose that the AG uptake into rat hepatoma cells is mediated by a carrier distinct from glucose transporters.

Ligand binding of bovine carboxypeptidase B. IV. Oligopeptide substrates and extended active center.

Catalytic and binding properties of bovine carboxypeptidase B were studied by kinetic and affinity chromatographic methods both using several oligopeptides as substrates or immobilized ligands. These oligopeptides contained either arginines or phenylalanines at carboxy termini as well as phenylalanyl residues in one of the other positions. The chromatographic studies showed that the phenylalanyl residues in endo-positions play a significant role in binding of the immobilized peptides to the enzyme, while the kinetics studies indicated further that the presence of an internal hydrophobic residue in a substrate was advantageous for the catalytic release of the carboxyl terminal residue from the substrate. These observations support the supposition that the enzyme has an extended active center which contains an extended hydrophobic binding site. Several hydrophobic compounds, which have been shown to act as activators in dipeptide substrate hydrolyses, showed inhibitory effect on hydrolyses of oligopeptide substrates. This observation suggests that these hydrophobic compounds bind to a portion of the hydrophobic site in the active center.

Purification and some properties of a hepatic NADPH-dependent reductase that specifically acts on 1,5-anhydro-D-fructose.

Glycogen gives rise to 1,5-anhydro-D-fructose (AF), which is then reduced to 1,5-anhydro-D-glucitol (AG) in animal livers. An enzyme that catalyzes NADPH-dependent reduction of AF to AG was isolated and purified to homogeneity from porcine liver. Its apparent molecular mass was about 38 kDa on the basis of SDS-PAGE, and its monomeric dispersion in aqueous solution was indicated by gel filtration on a Superose 12 column. Amino acid sequences were determined for four peptides obtained from the purified enzyme. The resulting sequences covered about 50% of the whole sequence and indicated a remarkable similarity between the enzyme and aldose reductase. The purified enzyme showed molecular activity of 8.7 s(-1) on the basis of a molecular mass of 38 kDa, and a Km value of 0.44 mM for AF at the optimum pH of 7.0. It reduced pyridine-3-aldehyde and 2,3-butanedione effectively, acetaldehyde, glucosone, and glucuronic acid poorly and showed no detectable action on glucose, mannose and fructose. It was inactivated by p-chloromercuribenzoic acid to a considerable extent, and the inactivation was partially reversed by 2-mercaptoethanol treatment. It was also sparingly inhibited by relatively high concentrations of glucose, glucose-1(6)-phosphate and 1,5-anhydroglucitol. The reverse reaction, i.e., NADP+-dependent AG oxidation, was not observed. The observed catalytic properties and partial amino acid sequences rule out the possibility that the isolated protein is identical with any known reductase.

Phosphorylation of 1,5-anhydro-D-glucitol in mammalian cells.

A cyclic polyol, 1,5-anhydro-D-glucitol (AG), is generally present in animals, although little is known about the metabolic and physiological roles of AG in any type of animal cells. The present metabolic study demonstrated phosphorylation of AG in human chronic myelogenous leukemia cells, K-562. Phosphorylated AG (AGP) was also proved to be present in various rat organs; its level in most organs ranged between 2 and 5 nmol/g wet tissue, which amounted to 5 to 10% of the AG levels in the respective organs. In the spleen and brain, however, the AGP levels were especially high, 13.4 and 8.3 nmol/g, respectively, or 24.4 and 20.6% of the respective AG levels. These data suggest that AGP is an intermediary metabolite related to AG in animal cells.

Identification and characterization of positive regulatory elements in the human glyceraldehyde 3-phosphate dehydrogenase gene promoter.

The gene for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is expressed at high levels in almost all tissues. However, the molecular mechanism which sustains high-level expression of this house-keeping enzyme is still unknown. Here we show that transcriptional activity is reduced by deletion of the nucleotides from -181 to -144 (relative to the transcriptional start site) in the promoter of human GAPDH gene, both in CHO (derived from Chinese hamster ovary) and HepG2 (derived from human hepatoma) cells. Gel retardation assays revealed that at least two nuclear factors, termed GAPBF1 and GAPBF2, bind to this region. Mutations in the GAPBF1 binding site (-178 to -169) or the GAPBF2 binding site (-168 to -163) reduced this promoter activity in vivo, showing that these two sites contribute to the activity of the GAPDH gene promoter. Since mutations in the region from -162 to -146 also reduced the promoter activity, this region seemed to function as an added cis-element, although we failed to find a factor that interacted specifically with this region in vitro. Accordingly, we propose that there are multiple cis-elements in the region from -181 to -144, each of which contributes to the promoter activity of GAPDH gene; the GAPBF1 binding site has the unique feature of having a stretch of repeated A nucleotides.

Ligand bindings of bovine carboxypeptidase B. II. Affinity chromatography and cooperative ligations.

Affinity chromatography was used to characterize the binding properties of carboxypeptidase B with its ligands. The affinity adsorbents employed included arginine directly attached to agarose beads, arginine attached to the same support through hydrophilic and hydrophobic spacers, and immobilized caproylphenylalanine. The enzyme showed marked retardation on all of the arginine columns but only slight retardation on the phenylalanine column. Several hydrophobic ligands in solution enhanced to some extent the enzyme retardation on columns having arginine directly attached to the solid support, while several amino- and guanidino-alkylcarboxylic acids (lysine and arginine analogs) greatly enhanced the enzyme retardation on the phenylalanine column and somewhat enhanced it on the other columns having hydrophobic spacer arms. These observations confirmed that the enzyme has twobinding sites for the soluble and immobilized ligands and that these two sites exhibit cooperative ligations. Binding constants of the enzyme for various soluble ligands were also calculated from their chromatographic effects and the resulting values were interpreted in terms of the cooperative action of the two bindings sites, i.e., one for the primary binding of basic amino acid analogs (SITE I) and the other for hydrophobic compounds (Site II). In this chromatographic study, however, such cooperation of the two sites was obscure when arginine, acylarginine, or alkylarginine was the ligand directing to Site I.

Reduced levels of plasma 1,5-anhydroglucitol in diabetic patients.

Anhydroglucitol in human plasma was studied by high pressure liquid chromatography, which was employed to simplify sampling procedures for the polyol assay and to avoid enzymatic treatment of the plasma for removal of glucose. Polyols in the column effluent were assayed by a flow fluorometric method, which involved two continuous successive reactions; periodate oxidation and the Hantzsch reaction. Plasma, 1 ml each, from 55 diabetic and 18 control subjects was deproteinized, concentrated, and subjected to the liquid chromatography. The results of this analysis indicated that the plasma anhydroglucitol level showed an inverse correlation with the plasma glucose level, while the correlation of glycerol and glucose levels was obscure.

A unique specificity of a calcium activated neutral protease indicated in histone hydrolysis.

Calf thymus histones were found to be susceptible to a calcium-activated neutral protease [CANP: EC 3.4.22.17] which required a high concentration of calcium ions for its activity (mCANP). The susceptibilities of histones were in the order of relative degradation rate: H2B, H2A, and H3. The major peptide fragments released by CANP from H2A, H2B, and H3 were isolated and the cleavage sites were determined. Examination of amino acid sequences and environmental features around the cleavage site as well as kinetic analysis of the degradation process led us to the following conclusions about the mode of substrate recognition of mCANP: 1) The cleavage sites in histones could not be interpreted in terms of the primary structure around them. Thus, it seems unlikely that the specificity of CANP solely depends on its recognition of any specific amino acid residues or sequences. 2) The susceptible bonds were never located in the midst of either a hydrophobic or hydrophilic alignment of amino acid residues but in the vicinity of the boundary between hydrophilic and hydrophobic clusters. 3) Once a peptide fragment was generated by the proteolytic degradation, no further cleavage occurred even if the peptide still contained a bond corresponding to what was susceptible to CANP in an intact histone. This observation was interpreted to mean that CANP may recognize a certain higher order structure of its substrates.

Synthesis of 1,5-anhydro-D-glucitol from glucose in rat hepatoma cells.

A pyranoid polyol, 1,5-anhydroglucitol (AG), generally occurs in the human body as a humoral component. The plasma AG concentration in healthy individuals is maintained at a constant level, but it is markedly decreased in diabetes mellitus. This is due to hyperglycemia-dependent abolishment of renal AG retention. Hence, the plasma AG concentration has been established as a clinical marker for duration of hyperglycemia and since 1991 it has been practically applied to diabetic care in Japan. However, the details of the metabolism of AG and its physiological significance generally remain to be studied. In this study, we confirmed AG synthesis in cultured cells of a rat hepatoma line, Reuber H-35, in which AG was found to be derived from glucose, with retention of all six carbon atoms in the pyranoid structure. The fraction of the total glucose consumed by the cells, which was converted to AG (conversion efficiency) was at most 5 x 10(-6). The conversion efficiency increased at higher glucose concentrations (mM orders) where the glucose consumption rate was saturated. Since the rate of the hexokinase reaction, one of the rate-limiting steps in glucose consumption, has been estimated to be saturated at microM orders of glucose concentration, this observation was interpreted as indicating that AG is synthesized through a pathway which does not share the hexokinase reaction with glucose utilization. The presence of precursors other than glucose was also indicated in the time-course study of AG synthesis. Further, the amount of AG synthesized daily in humans is significant in comparison with the amount obtained from the diet.

Oxidation of 1,5-anhydro-D-glucitol to 1,5-anhydro-D-fructose catalyzed by an enzyme from bacterial membranes.

Bacteria which grow on 1,5-anhydro-D-glucitol (AG) were isolated from soil. One such strain showing the highest AG-assimilating activity was further characterized and identified as a new strain of the Pseudomonas family (named Pseudomonas sp. NK-85001). A subcellular membranous fraction obtained from this strain catalyzed the oxidation of AG to 1,5-anhydro-D-fructose. This oxidation reaction consumed molecular oxygen as the terminal electron acceptor. The AG-oxidizing activity was further purified after solubilization. The AG oxidation catalyzed by this solubilized enzyme utilized molecular oxygen only in the presence of an electron mediator such as 2,6-dichlorophenolindophenol or phenazine methosulfate. Thus, the enzyme was suggested to be a dehydrogenase rather than an oxidase. The solubilized enzyme preparation also showed a strict substrate specificity. The observed specificity indicated that application of the enzyme for AG assay in clinical samples might be possible.

1,5-Anhydroglucitol promotes glycogenolysis in Escherichia coli.

Glycogen is a storage compound that provides both carbon and energy, but the mechanism for the regulation of its metabolism has not been fully clarified. Recently, we found a new glycogenolytic pathway in rat liver in which glycogen is first metabolized to 1, 5-anhydrofructose (AnFru) and then to 1,5-anhydroglucitol (AnGlc-ol). Because the amounts of glycogen and AnFru are closely related in various rat organs and the second reaction, AnFru to AnGlc-ol, is strongly inhibited in the presence of glucose, we expected that this pathway might play a regulatory role in glycogen metabolism. Here we evaluate the expected involvement of AnGlc-ol and AnFru in the regulatory mechanism in Escherichia coli C600. Having established the presence of this new glycogenolytic pathway in E. coli C600, we further show that the conversion of AnFru to AnGlc-ol is activated only after the exhaustion of glucose in the medium, and that as little as 5 microM AnGlc-ol in the medium acutely accelerates the degradation of glycogen by 40%. We consider the role of AnGlc-ol in the mechanism that controls glycogen metabolism in E. coli to be as follows. When glucose is abundant, E. coli accumulate glycogen, a fraction of which is steadily degraded so that the amount of AnFru is about 1/1,000 of glycogen on a weight basis. When glucose is depleted and the demand for glycogen utilization is elevated, AnFru, which has accumulated mostly in the medium, is promptly taken up and converted to AnGlc-ol, which accelerates glycogen degradation. We also suggest the possibility that AnGlc-ol is one of the extracellular signaling molecules for bacteria.

Escherichia coli phosphorylates 1,5-Anhydroglucitol and releases 1,5-Anhydroglucitol 6-phosphate when glucose is absent in the medium.

The cyclic polyol 1,5-anhydro-D-glucitol (AG) is detected in most organisms, but little is known about its metabolism and physiological roles. Our previous study demonstrated that Escherichia coli C600 synthesizes AG when glucose is exhausted in the medium and that it temporarily releases AG into and then takes it back from the medium, thus forming a sharp peak in AG concentration in the medium a few hours after reaching stationary growth phase. The present study demonstrates that when glucose is absent in the culture medium, E. coli C600 takes up and phosphorylates AG and releases a large portion of it back into the medium in the form of a phosphate ester. [U-13C]AG was added to the medium after the exhaustion of glucose and the resulting [U-13C]AG phosphate was partially purified by several steps of anion exchange chromatography and identified as AG 6-phosphate by 13C-NMR. The identity of the phosphate ester was also confirmed by GC-MS analysis after further purification.

NMR of all-carbon-13 sugars: an application in development of an analytical method for a novel natural sugar, 1,5-anhydrofructose.

Of the all-carbon-13 compounds, glucose is one of the most easily accessible, and therefore we applied 13C-NMR technique to the metabolic study of glucose-related compounds, 1,5-anhydro-D-glucitol and 1,5-anhydro-D-fructose (AF). Applying an INADEQUATE method to the substitutes of these novel sugars fully labeled with carbon-13, we could trace out the entire carbon skeleton with high sensitivity and confirm the chemical structures of these sugars. The method also provided a much easier way to optimize the enzymatic oxidation for AF preparation: we selectively and continuously monitored the quantities, as well as their structures in aqueous solution, of the substrate and products in a noninvasive manner. Similarly relying upon information from the 13C-NMR, we developed a valuable derivatization method of AF for its GC-MS application, which was so sensitive that we were able to demonstrate the natural occurrence of AF in rat liver.