A manganese-containing catalase has been characterized from Thermokophilum album NM, a gram-negative aerobic bacterium obligate for thermophily and n-alkane substrates. The level of catalase in cells was increased about ninefold by growth in the presence of paraquat (2.5 pM), a superoxide-generating toxicant. Superoxide dismutase levels were unaffected by this compound. The enzyme was purified from cultures grown in the presence of paraquat to >95% homogeneity and had an Mr of 141,000. The enzyme was composed of four subunits, and each had an Mr of 34,000. There were 1.4 ± 0.4 atoms of manganese present per subunit. The catalase had a K. for hydrogen peroxide of 15 mM and a V,,,. of 11 mM/mg. Peroxidase activity, as measured with p-phenylenediamine, copurified with the catalase. Inhibitors of heme-catalase were weak inhibitors of the T. album enzyme. The optimum pH for catalase activity was 8 to 9. The enzyme was stable from pH 6.5 to 11and retained activity at assay temperatures from 25 to 80°C. The catalase was stable for 24 h of incubation at 600C.

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Faecal concentrations of short chain fatty acids (SCFAs) and faecal water content were determined in 93 healthy volunteers. We found positive correlation between faecal water content and the concentration of acetic, propionic and butyric acid. Multiple correlations between different SCFAs were found and grouping of the correlations according to an assumed substrate specificity was observed. Acetic, propionic and n-butyric acid, that are derived from carbohydrates, were best related to each other, whereas the minor acids, derived mostly from proteins, formed another group. Some specific features of the branched chain fatty acids (iso-acids) were discovered: their faecal concentrations were very strongly correlated to each other (Rho=0.977), they did not correlate with the total concentration of SCFAs, and showed negative correlations to the faecal water content. These findings suggest that the iso-acids have common and specific substrates in viva, possibly of endogenous origin.

To determine the effect of olestra on microbial ecology of the gut, faecal short-chain fatty acids (SCFAs) and water content were assessed in 93 subjects in a 36 d parallel, placebo-controlled, double-blind study. Faecal SCFAs and water content were determined at the end of an 8 d low fibre baseline period and 28 d treatment period. The test meal consisted of either a moderate (7 g) or high (24 g) level of fibre and olestra (24 g) or an equivalent amount of conventional fat. Olestra had a significant effect on both faecal water content and SCFAs. The water content decreased and concentrations of some SCFAs increased. The effect of olestra on SCFA concentrations in faeces (mmol/kg) differed with different fibre content of the meal. When the SCFAs were expressed as mmol/l faecal water, a similar pattern of changes (several SCFAs increased) was observed for both olestra groups. Although all individual SCFA values were within the range of a healthy population, the effects were consistent, and potential reasons for it are discussed.