Effect of nonionic detergents on the activity of a thermostable lipase from Bacillus stearothermophilus MC7

The influence of nonionic surfactants on the activity of a novel thermostable lipase from Bacillus stearothermophilus MC7 was investigated with a view to its potential for synthesis of structured lipids. A large number of modifiers within a broad concentration range were applied. The activity of the enzyme was measured at a relatively high reaction temperature. Highest degree of activation was observed when PEG₆₀₀₀ was applied (up to 2.3-fold increase). Modification essentially changed the performance of the lyophilised preparations—they keep up to 80% of the activity of the native enzyme in the presence of a detergent against 30% in its absence. The effect of sorbitan esters (spans) and polyoxyethylene derivatives of sorbitan esters (tweens) on lipase MC7 was estimated, their HLB value varying within the interval 2.1–16.7. Tweens were strong inhibitors at higher concentrations. For all spans, excepting span 60, an increase of enzyme activity with concentration was observed. All studied additives slow down the process of thermal denaturation. Lipase preparations preserve more than 60% of their activity after 30-min incubation at 75 °C in the presence of tween 60 or PEG₄₀₀₀.     

Variability in several ecologic-physiologic traits of different populations of the Asiatic Arctic suslik Citellus parryi]

In several geographic populations of the Arctic ground squirrel C. parryi, studies have been made on changes in oxygen consumption during decrease of the ambient temperature from 25 to 3-4 degrees, thermal preference, hemoglobin content of the blood and composition of the adipose tissue (both brown and white, subcutaneous and visceral). Significant shifts of these indices were found. In animals from various parts of the species area, different sensitivity to cooling was found, as indicated by determinations of oxygen consumption at different temperatures and the prefered temperature: different hemoglobin content of the blood was also found together with differences in the level of two unsaturated fatty acids - the oleic and linoleic ones. Comparison of these data with similar results obtained on various populations of the Siberian ground squirrel C. undulatus revealed obvious differences between these close species with respect to the indices studied.     

The bacteriorhodopsin proton pump: effect of crosslinkings of lysine residues

All six available lysine residues in bacteriorhodopsin were amidinated with dimethyl-3,3'-dithiobispropionimidate, which is a crosslinking agent. The photocycle was studied by measuring light absorption and electric signals. The data show an essential change in the photocycle: instead of single components, the rise of the signal due to the M intermediate can be decomposed into two components, and the decay into three. The life-times and the intensities of these components and in general the proton pumping activity of bacteriorhodopsin depend only negligibly upon pH. Changes upon removing the crosslinks are not significantly different from those in the crosslinked samples. The lysine residues therefore may not be considered of primary importance in proton translocation.