Mammalian temperature stability

Ox-liver /3-glucuronidase was found to be stable to 30 minutes of heating at 50°, but there was considerable inactivation42 at 55°. Heating a limpet preparation (of pH 5) for 5 minutes caused a 15% inactivation86 of /3-glu-curonidase at 60° and 35% at 70°. Within the range of temperature-stability of the enzyme, mammalian /3-glucuronidase activity was approximately doubled for every 10° rise in temperature.81 -147 1 66 This would also appear to be true of mollusc preparations.107171 ... 

The widespread agricultural use of the OPPs and their potential mammalian toxicity has dictated the development of several methods for isolating and detecting the parent compounds. A method that allows the extraction and simultaneous detection of OPPs and their primary and secondary metabolites from beef tissue was developed using HPLC-DAD with a gradient mobile phase (96). Information on the thermal decomposition of OPPs in meat and other food products is still very limited. The temperature and pH stabilities of OPPs were investigated in lean beef... 

The present study indicates that the extracellular enzyme, pepsin, exhibits striking differences from its mammalian homologue with respect to optimum pH, Ea for catalysis, thermal stability, and substrate affinity. These data are interesting from the viewpoint of biological adaption at low temperatures, but they also provide some substance to our contention that enzymes from fish plant wastes can have sufficiently unique properties to justify their use over conventional sources of enzymes used as food-processing aids. The relatively low Eas for protein hydrolysis by fish pepsins indicate they may be especially useful for protein modifications at low temperatures. Alternatively, the poor thermal stability of the fish pepsins studied indicate that the enzymes can be inactivated by relatively mild blanching temperatures. The reality of this concept will have to await studies where the pepsins are used as food-processing aids. Such studies are currently underway in our laboratory. 

Biophysical studies on membrane lipids coupled with biochemical and genetic manipulation of membrane lipid composition have established that the L state of the membrane bilayer is essential for cell viability. However, membranes are made up of a vast array of lipids that have different physical properties, can assume individually different physical arrangements, and contribute collectively to the final physical properties of the membrane. Animal cell membranes are exposed to a rather constant temperature, pressure, and solvent environment and therefore do not change their lipid makeup dramatically. The complex membrane lipid composition that includes cholesterol stabilizes mammalian cell membranes in the L phase over the variation in conditions they encounter. Microorganisms are... 

Similar arguments relative to the importance of hydrogen bonding in collagen fibrillar structure are also derived from a comparison of the shrinkage temperatures and compositions of mammalian and fish skin collagens. The latter, which possesses (see Section II, 5) fewer hydrox-ylic side chains than does the former, also has less hydrothermal stability (92). 

The initial series of experiments assessed the stability of the conjugates to the pH and temperature conditions (37 °C) found in the mammalian GIT pH 1 and pH 9 were chosen to represent the normal extremes of acidity and basicity in the human. While pH 5 provided an intermediary value, it is also relevant to parts of the ruminant digestive system. The rate of degradation of the conjugates was monitored over a 24-hour period by LC-MS/MS (turbo ion spray interface). Optimization of the LC system provided an efficient method in which several compoimds could be analyzed simultaneously. During the early... 

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