Protein factors affecting biological activity

Several factors affect the selection of the buffer solution, such as the optimum pH the buffer anionic or cationic species (which can interfere in the subsequent purification steps) the pH variation with ionic strength or temperature the buffer reactivity with the proteins in solution the biological activity (e.g. phosphates can inhibit or activate a protein in biological reactions) the interaction of the buffer with other components the buffer permeation in biological membranes the toxicity the light absorption at 280 nm the cost (especially if used in large-scale processes) and the protein solubility. 

Temperature affects the loss of biological activity versus dose curves of proteins (Fluke, 1966). About 2.9-fold more dose is required to inactivate a given proportion of the molecules in a preparation at — 135°C than at 30°C. This observation is valid for all proteins studied, and the 2.9-fold correction factor was applied to obtain Mr from equation (4) when D37 was measured at -135°C (Kempner and Haigler, 1982). 

Despite the fact that a plethora of dietary factors could, and will, affect the absorption characteristics of phytochemicals, this area has not been systematically explored. One reason might be the complexity of dietary factors and their interactions that could affect absorption. A nonexhaustive list would include the volume and composition of the food consumed, pH, caloric density, viscosity, nutrients (carbohydrates, protein, fat, fibers), alcohol, caffeine, and the presence of other phytochemicals. Such dietary factors affect the functional status, motility, and acidity of the gastrointestinal tract in a complex manner and modify the physicochemical properties, formulation, and dissolution characteristics of the compound of interest. Calcium in dairy products, for example, has the potential to chelate tetracyclines and fluoroquinolones and, thereby, reduce their bioavailability and biological activity [31]. 

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