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Aims:  We found that an adenine base caused fluorescence quenching of a fluorescein (FL)‐labelled probe in DNA:RNA hybrid sequences, and applied this finding to a nucleic acid sequence–based amplification (NASBA) method. Methods and Results:  The present NASBA method employed a probe containing an FL‐modified thymine at its 3′ end and ethidium bromide (EtBr) on the basis of a combination of adenine‐induced quenching and fluorescence resonance energy transfer (FRET) between the FL donor and EtBr acceptor. This NASBA was used to detect Shiga toxin (STX) stx‐specific mRNA in STX‐producing Escherichia coli, demonstrating rapid quantification of the target gene with high sensitivity. Conclusion:  Although the inherent quenching effect of adenine was inferior to that of guanine, FRET between the FL and EtBr moieties enhanced the adenine‐induced quenching, allowing rapid and sensitive real‐time NASBA detection. Significance and Impact of the Study:  This study gives a novel real‐time diagnostic system based on NASBA for a sensitive mRNA (or viral RNA) detection.

For the purpose of quality evaluation of magnesium oxide (MgO) tablets, we considered the dissolution test method with changes in the pH of the dissolution medium as an indicator and studied the elution behavior of MgO from commercial MgO tablets. We also studied the effects of particle size on the elution rate of MgO from MgO tablets. A dissolution test was carried out using the rotating basket method in 100 ml of the first fluid (pH 1.2). The stirring speed was set at 200 rpm. The elution behaviors of MgO from two products were markedly different. The medium pH for the sample MM (Magmit) tablet after 15 min reached 9.5 but that for ML (Maglax) tablet was 2.7 even after 60 min. The apparent solubility of MgO in 100 ml of the first fluid were, respectively, 175 mg and 100 mg when medium pH as 9.5 and 1.5. The low dissolution of ML tablets is thought to be due to the large particle size (average particle size r = 226 microm) or due to the effects of additives on elution. These results suggest that neutralizing activity after ingestion of MgO tablets and subsequent laxative effects may, when conditions after ingestion of MM tablets and after ingestion of ML tablets are compared, produce differences between them. We found that the dissolution test method with pH as an indicator is useful in assessing the dissolution behavior of MgO preparations.

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