NITRITE REDUCTASE IN SALMONELLA TYPHIMURIUM

A nitrite reductase was identified and purified 11 -fold from the cytoplasmic fraction of Salmonella typhimurium grown anaerobically with nitrite as the sole nitrogen source. The enzyme required NADH as a cofactor and showed maximum in vitro reductase activity at pH 8.0.
S. typhimurium, grown anaerobically in glucose-limited minimal medium containing peptone and nitrite, showed shorter generation times and increased cell yields in comparison to nitrite-free cultures. The presence of nitrite had no effect on aerobic cultures. The nitrite reductase functions in a dissimilatory manner and appears to be primarily involved in physiological energy generation during anaerobic growth. The nitrite reductase may function to remove excess reducing power in the form of NADH from the cell thus increasing ATP production during the anaerobic fermentation of glucose. The formation and subsequent assimilation of ammonia from nitrite is of secondary importance to the organism.     

Contribution of Lactobacillus plantarum and Leuconostoc mesenteroides subsp. mesenteroides to Atypical Odors of Beef Strip Loins

Sterile beef strip loin tissue was inoculated with Lactobacillus plantarum or Leuconostoc mesenteroides subsp. mesenteroides, placed in sterile sample bottles which were purged with CO₂, and stored up to 28 days at 3°C. Volatile compounds detected in the headspace of these samples included acetone, toluene, acetic acid, ethyl acetate, a C₇ hydrocarbon, and trichloromethane. The profile of volatiles in packaged sterile loin tissue stored for up to 28 days was similar. However, the inoculated samples spoiled (soured) at a faster rate.     

Vitrification of aqueous suspensions from a controlled environment for electron microscopy: An improved plunge-cooling device

In the process of vitrifying aqueous suspensions for cryotransmission electron microscopy, water is solidified without crystallization. Vitrification can be achieved by rapidly plunging an aqueous thin film into a liquid cryogen. The preparation of aqueous thin films prior to vitrification must be performed in an environmental cabinet at controlled temperature and humidity in order to prevent evaporation and temperature-induced phase changes in the thin film. The device described here incorporates several important features which make the apparatus simpler and more convenient to use than similar devices described in the literature. One of these features includes the use of a totally enclosed environmental cabinet in which the grid, sample, micropipette and absorbent paper are equilibrated before thin-film preparation. Other features include a cryogen dewar on a swing arm for easy refilling, a guillotine shutter which is used to trigger the plunger electrically and a semiautomatic system which facilitates rapid transfer of the vitrified specimen from liquid propane to liquid nitrogen for storage and reduces handling of the specimen. To demonstrate the utility of the device, results showing the influence of temperature on the morphology of phospholipid vesicles are presented. A commercial cryotransfer apparatus (which is used for transportation of the vitrified specimen to the electron microscope cold-stage) has been modified to reduce the possibility of reversion of the vitreous phase to the crystalline ice phases.     

Factors Affecting 1-Octen-3-ol in Mushrooms at Harvest and During Postharvest Storage

Harvesting experiments revealed that immature whole mushrooms with closed veils had higher 1-octen-3-0l levels than more mature whole mushrooms with open veils. The l-octen-3-01 content of the gills was higher in immature mushrooms with closed veils, gradually decreased with maturity as the veil opened, and finally increased after the gills were well exposed. Postharvest experiments demonstrated that storage temperature influenced the activity of lipoxygenase-hydroperoxide lyase, but no differences in 1-octen-3-01 content were observed. Enzyme activity as well as 1-octen-3-01 content decreased during storage. Addition of calcium chloride to irrigation water, employed to improve quality and shelf life of fresh mushrooms, increased the amount of l-octen-3-01 immediately after harvest.     

TENSOR-AIDED GEARBOX MODELLING

This paper develops an electrical analogue for a gearbox suitable for use in the time-domain modelling of many electromechanical systems, with tensor methods being used to define the changing conditions in the gearbox brought about by backlash. Unlike most existing models it is compatible with the time-varying and discontinuous models often used to describe the electrical items of a typical system, and it allows for the effects of these items of mechanical non-linearities and discontinuities such as friction and backlash.     

Lack of Vitamin B6 Activity of 6-Hydroxypyridoxine

Hydroxylation of the C-6 position of pyridoxine has been described recently as a mechanism for the degradation of vitamin B6 in foods. The nutritional properties of the resulting 6-hydroxypyridoxine in mammals have not been previously evaluated. 6-Hydroxypyridoxine was synthesized and its structure confirmed by UV and NMR spectroscopy. A rat bioassay with multiple dose levels was conducted to compare the vitamin B6 activity of pyridoxine and 6-hydroxypyridoxine with respect to a variety of indices of vitamin B6 metabolism. By all criteria employed, 6-hydroxypyridoxine exhibited neither vitamin B6 nor antivitamin B6 activity and, thus, is nutritionally inert.     

Quantitative Analysis of Carotenoids and Carotenoid Esters in Fruits by HPLC: Red Bell Peppers

The carotenoids of red bell peppers were analyzed without saponifi-cation by high performance liquid chromatography using octadecyl silica as stationary and methanol-ethyl acetate as mobile phases. The red bell peppers contained 280 ug/gm total carotenoids. Capsanthin accounted for 60% of the total carotenoids. Also present were 11%beta-carotene and 20% capsorubin. Capsanthin was acylated with C₁₂ to C₁₈ saturated fatty acids.