Since the beginning of investigations of the Na,K-ATPase, it has been well-known that Mg is an essential cofactor for activation of enzymatic ATP hydrolysis without being transported through the cell membrane. Moreover, experimental evidence has been collected through the years that shows that Mg ions have a regulatory effect on ion transport by interacting with the cytoplasmic side of the ion pump. Our experiments allowed us to reveal the underlying mechanism. Mg is able to bind to a site outside the membrane domain of the protein's α subunit, close to the entrance of the access channel to the ion-binding sites, thus modifying the local concentration of the ions in the electrolyte, of which Na, K, and H are of physiological interest. The decrease in the concentration of these cations can be explained by electrostatic interaction and estimated by the Debye-Hückel theory. This effect provokes the observed apparent reduction of the binding affinity of the binding sites of the Na,K-ATPase in the presence of various Mg concentrations. The presence of the bound Mg, however, does not affect the reaction kinetics of the transport function of the ion pump. Therefore, stopped-flow experiments could be performed to gain the first insight into the Na binding kinetics on the cytoplasmic side by Mg concentration jump experiments.

Highly substituted arenesulfonates are chemically stable compounds with a range of industrial applications, and they are widely regarded as being poorly degradable. We did enrichment cultures for bacteria able to utilise the sulfonate moiety of 14 compounds, and we obtained mixed cultures that were able to desulfonate each compound. The products formed were usually identi®ed as the corresponding phenol, but because we could not obtain pure cultures, we followed up these ®ndings with quantitative work in pure cultures of, e.g., Pseudomonas putida S-313, which generated the same phenols from the compounds studied. Many of these phenols are known to be biodegradable, or to be subject to binding to soil components. We thus presume that the capacity to degrade aromatic sulfonates extensively is widespread in the environment, even though the degradative capacity is spread over several organisms and conditions.

Abstract-Earlier work shows that the biodegradation and biotransformation of commercial linear alkylbenzenesulfonate (LAS) as a carbon source for growth leads to a residue of sulfonated aromatic compounds, termed refractory organic carbon, from the synthetic by-products. We now show that this refractory organic carbon, after separation from sulfate ion, is utilized extensively as a sulfur source for bacterial growth. The products of desulfonation are expected to be biodegradable, so we question the value of adjectives like refractory.

Earlier work shows that the biodegradation and biotransformation of commercial linear alkylbenzenesulfonate (LAS) as a carbon source for growth leads to a residue of sulfonated aromatic compounds, termed refractory organic carbon, from the synthetic by‐products. We now show that this refractory organic carbon, after separation from sulfate ion, is utilized extensively as a sulfur source for bacterial growth. The products of desulfonation are expected to be biodegradable, so we question the value of adjectives like refractory.