Synthesis of 18O-labeled RNA for application to kinetic studies and imaging

Radioisotopes and fluorescent compounds are frequently used for RNA labeling but are unsuitable for clinical studies of RNA drugs because of the risk from radiation exposure or the nonequivalence arising from covalently attached fluorophores. Here, we report a practical phosphoramidite solid-phase synthesis of ¹⁸O-labeled RNA that avoids these disadvantages, and we demonstrate its application to quantification and imaging. The synthesis involves the introduction of a nonbridging ¹⁸O atom into the phosphate group during the oxidation step of the synthetic cycle by using ¹⁸O water as the oxygen donor. The ¹⁸O label in the RNA was stable at pH 3–8.5, while the physicochemical and biological properties of labeled and unlabeled short interfering RNA were indistinguishable by circular dichroism, melting temperature and RNA-interference activity. The ¹⁸O/¹⁶O ratio as measured by isotope ratio mass spectrometry increased linearly with the concentration of ¹⁸O-labeled RNA, and this technique was used to determine the blood concentration of ¹⁸O-labeled RNA after administration to mice. ¹⁸O-labeled RNA transfected into human A549 cells was visualized by isotope microscopy. The RNA was observed in foci in the cytoplasm around the nucleus, presumably corresponding to endosomes. These methodologies may be useful for kinetic and cellular-localization studies of RNA in basic and pharmaceutical studies.     

Metabolism of 3-phosphoglyceroyl phosphate in phosphoenolpyruvate-enriched human erythrocytes

The concentration of 3-phosphoglyceroyl phosphate in erythrocytes was increased by more than 100-fold when red cells were incubated with extracellular phosphoenolpyruvate at 37 degrees C. Since these elevated levels were maintained for 60 min, the metabolism of 3-phosphoglyceroyl phosphate and related compounds could be investigated in phosphoenolpyruvate-treated erythrocytes. 2,3-Bisphosphoglycerate synthesis was not affected by intracellular pH when the 3-phosphoglyceroyl phosphate level was constant but did vary with 3-phosphoglyceroyl phosphate concentration. On the other hand, the relationship between the rate of 2,3-bisphosphoglycerate synthesis and 3-phosphoglyceroyl phosphate concentration was not straightforward. At relatively low concentrations of 3-phosphoglyceroyl phosphate, the observed rate of 2,3-bisphosphoglycerate synthesis agreed with a rate calculated from a formula incorporating kinetic parameters of purified 2,3-bisphosphoglycerate synthase (Rose, Z.B. (1973) Arch. Biochem. Biophys. 158, 903-910). However, at high concentrations of 3-phosphoglyceroyl phosphate, the observed rate of 2,3-bisphosphoglycerate synthesis was lower than the calculated value. The concentration of glucose 1,6-bisphosphate did not increase even when 3-phosphoglyceroyl phosphate was elevated to 200 microM. Elevated levels of intracellular 2,3-bisphosphoglycerate did not inhibit glycolytic activity in these erythrocytes. These results suggest that incubation of erythrocytes with phosphoenolpyruvate is a useful technique to investigate the effect of metabolic perturbations at the intermediate stages of glycolysis.     

A survey for Yersinia pseudotuberculosis in migratory birds in coastal Japan

Yersinia pseudotuberculosis was isolated from three specimens of two species of birds, the black-faced bunting (Emberiza spodocephala) and pied wagtail (Motacilla alba), of 528 specimens of birds examined from coastal regions in Japan. The two isolated strains of Y. pseudotuberculosis were identified as serovar 4b and serovar 3. This is the first isolation of Y. pseudotuberculosis from birds in Japan. Yersinia enterocolitica was isolated from three specimens of the pied wagtail, one specimen of the reed bunting (Emberiza schoeniclus) and one specimen of the rustic bunting (Emberiza rustica). Yersinia frederiksenii was isolated from two specimens of the gray-rumped sandpiper (Heteroscelus brevipes). Yersinia intermedia was isolated from one specimen of the pied wagtail.     

Two distinct O-methyltransferases in aflatoxin biosynthesis

The substances belonging to the sterigmatocystin group bear a close structural relationship to aflatoxins. When demethylsterigmatocystin (DMST) was fed to Aspergillus parasiticus NIAH-26, which endogenously produces neither aflatoxins nor precursors in YES medium, aflatoxins B1 and G1 were produced. When dihydrodemethylsterigmatocystin (DHDMST) was fed to this mutant, aflatoxins B2 and G2 were produced. Results of the cell-free experiment with S-adenosyl-[methyl-3H]methionine showed that first the C-6-OH groups of DMST and DHDMST are methylated to produce sterigmatocystin and dihydrosterigmatocystin (O-methyltransferase I) and then the C-7-OH groups are methylated to produce O-methylsterigmatocystin (OMST) and dihydro-O-methylsterigmatocystin (DHOMST) (O-methyltransferase II). However, no methyltransferase activity was observed when either OMST, DHOMST, 5,6-dimethoxysterigmatocystin, 5-methoxysterigmatocystin, or sterigmatin was incubated with the cell extract. Treatment of the cell extract with N-ethylmaleimide inhibited O-methyltransferase I activity but not that of O-methyltransferase II. Furthermore, these O-methyltransferases were different in their protein molecules and were involved in both the reactions from DMST to OMST and DHDMST to DHOMST. The reactions described in this paper were not observed when the same mold had been cultured in YEP medium.     

Two distinct O-methyltransferases in aflatoxin biosynthesis.

The substances belonging to the sterigmatocystin group bear a close structural relationship to aflatoxins. When demethylsterigmatocystin (DMST) was fed to Aspergillus parasiticus NIAH-26, which endogenously produces neither aflatoxins nor precursors in YES medium, aflatoxins B1 and G1 were produced. When dihydrodemethylsterigmatocystin (DHDMST) was fed to this mutant, aflatoxins B2 and G2 were produced. Results of the cell-free experiment with S-adenosyl-[methyl-3H]methionine showed that first the C-6-OH groups of DMST and DHDMST are methylated to produce sterigmatocystin and dihydrosterigmatocystin (O-methyltransferase I) and then the C-7-OH groups are methylated to produce O-methylsterigmatocystin (OMST) and dihydro-O-methylsterigmatocystin (DHOMST) (O-methyltransferase II). However, no methyltransferase activity was observed when either OMST, DHOMST, 5,6-dimethoxysterigmatocystin, 5-methoxysterigmatocystin, or sterigmatin was incubated with the cell extract. Treatment of the cell extract with N-ethylmaleimide inhibited O-methyltransferase I activity but not that of O-methyltransferase II. Furthermore, these O-methyltransferases were different in their protein molecules and were involved in both the reactions from DMST to OMST and DHDMST to DHOMST. The reactions described in this paper were not observed when the same mold had been cultured in YEP medium.     

Stereochemistry during aflatoxin biosynthesis: cyclase reaction in the conversion of versiconal to versicolorin B and racemization of versiconal hemiacetal acetate.

(1'R,2'S)-(-)-aflatoxins are produced from racemic versiconal hemiacetal acetate (VHA) through complicated pathways, including a metabolic grid involving VHA, versiconol acetate (VOAc), versiconol, and versiconal (VHOH), and a reaction sequence from VHOH to versicolorin A (VA) through (-)-versicolorin B (VB) [or (+/-)-versicolorin C] (K. Yabe, Y. Ando, and Y. Hamasaki, J. Gen. Microbiol. 137:2469-2475, 1991; K. Yabe, Y. Ando, and T. Hamasaki, Agric. Biol. Chem. 55:1907-1911, 1991). In this study, we examined stereochemical changes of substances formed during the conversion of VHA to VA by using chiral high-performance liquid chromatography. In cell-free experiments using the cytosol of Aspergillus parasiticus NIAH-26, both (2'S)- and (2'R)-VOAc enantiomers were formed at about a 1:2 ratio from racemic VHA in the presence of NADPH and dichlorvos (dimethyl 2,2-dichlorovinylphosphate). Also, the esterase activity catalyzing the conversion of VHA to VHOH or of VOAc to versiconol did not show the stereospecificity for the 2' carbon atom of VHA or VOAc. However, when racemic VHA or racemic VHOH was incubated with the cytosol, (1'R,2'S)-(-)-VB was formed exclusively. Furthermore, only (1'R,2'S)-(-)-VB, and not (1'S,2'R)-(+) antipode, served as a substrate for desaturase activity in the microsome fraction catalyzing the conversion of VB to VA. These results demonstrate that the stereoconfiguration of bis-furan moiety in aflatoxin molecules is determined by the cyclase enzyme catalyzing the reaction from VHOH to VB, and the (1'R,2'S)-(-) configuration was further confirmed by the subsequent desaturase reaction. Remarkably, we found nonenzymatic racemization in both the (2'R)- and (2'S)-VHA enantiomers, and it was dependent upon the temperature and alkaline conditions.     

Accumulation of phosphoenolpyruvate in red cells incubated with the phosphate ester in an acidified isotonic sucrose medium.

Accumulation of exogenous phosphoenolpyruvate against the concentration gradient was observed when human red cells were incubated in an acidified isotonic sucrose medium. Fluoride increased the apparent accumulation by inhibition of the intracellular metabolic interconversion of the phosphate compound. The accumulation appeared to be specific for phosphoenolpyruvate and the accumulation rate for 3-phosphoglycerate, which has a molecular size and pKa similar to those of phosphoenolpyruvate, was less than one-tenth of the rate of phosphoenolpyruvate. Red cells incubated in the acidified sucrose medium tended to adhere to each other when examined with a scanning electron microscope.     

Effect of unusual polyamines on cleavage of DNA by restriction enzymes

The effect of unusual polyamines, such as thermine, caldopentamine, caldohexamine, tris(3-aminopropyl)amine, or tetrakis(3-aminopropyl)ammonium, on the activities of various restriction endonucleases was investigated by using an Escherichia coli plasmid as a substrate, which contains a high GC content fragment from an extreme thermophile. Restriction enzymes used were SmaI, BanII, NaeI, RsaI, and TaqI. Most of the polyamines tested were inhibitory to the enzyme activities. The larger and more branched a polyamine was, the more the activities of nucleases were inhibited. The inhibition was positively correlated with the polyamine concentration. The sites protected by a polyamine were identical to those protected by other polyamines, and also identical to those which were less sensitive to the restriction enzyme in the absence of polyamines. No sequence specificity was seen among these sites.     

Localization of aldosterone-producing adenoma: venous sampling in primary aldosteronism

Adrenal venous sampling of blood was performed for nine patients with aldosterone-producing adenoma (APA). Measurement of adrenal venous aldosterone is useful for localization of APA but difficult, because catheterization of the right adrenal vein is not easy, and the blood is diluted by nonadrenal flow. To solve these problems, levels of aldosterone (A; ng/dl) and cortisol (C; micrograms/dl) were measured in samples from the left adrenal vein (LAV) and the inferior vena cava (IVC), and the LAV A/C and (LAV A/C)/(IVC A/C) ratios were calculated. These ratios were also obtained for 16 patients with essential hypertension. The adenoma could be localized in three of the nine cases by the measurement of aldosterone alone, but the use of a LAV A/C ratio greater than 5 x 10(-3) and a (LAV A/C)/(IVA A/C) ratio less than 1.0 as criteria separated the patients into those with a left APA, right APA, or essential hypertension. Consequently, adrenal venous sampling and the calculation of these ratios enables preoperative localization of APA with more accuracy, especially when the tumor is small or the result of CT and adrenal scintigraphy is not consistent.