PubMed · 8798216
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S Doonan. 1996. Practical column chromatography.. https://doi.org/10.1385/0-89603-336-8%3A381
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Dimethyl sulfoxide (DMSO) occurs in the environment as a result of a number of biogenic and anthropogenic production and emission processes. It is an environmentally significant compound because of its use as a substrate by bacteria and its potential role in the biogeochemical cycle of dimethyl sulfide (DMS), a climatically active trace gas. In this paper, current methods for DMSO determination at nanomolar levels in natural waters, all involving gas chromatography, are reviewed. Direct injection and separation of aqueous DMSO offers a simple and fast application, but exhibits limited sensitivity due to limitation on injection volumes. So far, most authors have preferred DMSO reduction and subsequent analysis of the evolved DMS by purge-and-trap preconcentration and flame photometric detection. Several reducing agents have been used, though some require cumbersome procedures or are very sensitive to operational conditions. The common algal component dimethylsulfoniopropionate (DMSP) acts as an interference in some reduction methods and, therefore, either DMSP elimination prior to DMSO analysis or correction a posteriori is required. DMSO can be analyzed along with DMS, methanethiol, dimethyl disulfide and DMSP in the same water sample, either sequentially or separately, so that comprehensive speciation of methylated sulfur is obtained. Owing to the biological activity of DMSO, appropriate water sampling and handling procedures must be applied. Acidification and freezing appear to be suitable for aqueous DMSO storage, although immediate analysis in the field is always preferable. Future directions of DMSO determination in aquatic environments are suggested.
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Nuclear factor kappaB1 (NF-kappaB) is a heterodimeric complex that regulates transcription of many genes involved in immune and inflammatory responses. Its 50-kDa subunit (p50) is generated by the ubiquitin-proteasome pathway from a 105-kDa precursor (p105). We have reconstituted this proteolytic process in HeLa cell extracts and purified the responsible enzymes. Ubiquitination of p105 requires E1, and either of two types of E2s, E2-25K (for which p105 is the first proven substrate) or a member of the UBCH5 (UBC4) family. It also requires a new E3 of 50 kDa, which we call E3kappaB. This set of enzymes differs from the E2s and E3 reported by others to catalyze p105 ubiquitination in reticulocytes. The ubiquitinating enzymes purified here, together with 26S proteasomes, allowed formation of p50. Thus, the 26S proteasome provides all the proteolytic activities necessary for p105 processing. Interestingly, in the reconstituted system, as observed in cells, the C-terminally truncated form of p105, p97, was processed into p50 more efficiently than normal p105, even when both species were ubiquitinated to a similar extent. Therefore, some additional mechanism involving the C-terminal region of p105 influences the proteolytic processing of the ubiquitinated precursor.