Protein release constant

In a simple model of homogenization in a French press, the process of the disruption of the cell wall is modeled by a first-order law. Then, the amount of protein released, R, varies with the number of passes of broth through the homogenizer, N [Eq. (8.58)], where Rm3X is the maximum amount of protein obtainable through homogenization and k is a constant. 

Elvassore et al. (96) successfully microencapsulated insulin in poly(eth-ylene glycol) (PEG) of various molecular weights and PLA. Particles of a mean size between 400 and 700 nm were formed at 16-22°C and 13 MPa. The insulin retained more than 80% of its native activity in vivo. Release studies on particles containing PEG with a molecular weight <1900 were free of a burst effect and showed a slow constant protein release for 1500 h. Although these PCA-based microencapsulations were successful, high bursts have been reported for some systems [e.g., BSA in PLGA (90)]. 

A similar characterization for cells treated with 2M guanidine and 2% Triton is shown in Figure 2. The protein release, based on total cellular protein, levels off at 35%. RNA is released to a lesser extent ( , 15%) and very little DNA ( 5%) is released from the cells. The constant cell concentration indicates that the release is not the result of cell fragmentation. 

The insulin complex must first be degraded, because free insulin is the active form. Thus, the protein-protein interactions and also the zinc complexes must be disrupted. Because these interactions take time to disrupt, there is a lag time before the free insulin is released, resulting in slower onset. Because the complexed form allows more insulin to be administered per dose, the duration is long, because free insulin is released constantly upon disruption of the protein/zinc interactions. 

Both of these basic processes are used to produce microspheres that have different release characteristics. The microspheres may release the protein in either a continuous or a pulsatile manner. Two mechanisms control the release of the protein out of the microspheres. The first mechanism is the simple diffusion of the protein out of the polymer matrix. Typically, the diffusion process occurs in two or more stages comprising an initial release of protein at or near the microsphere surface followed by additional release of protein by diffusion from the microsphere s interior pores. The second mechanism is the erosion of the polymer matrix, which occurs by hydrolysis of the polymer backbone. For continuous release, the diffusion and erosion processes must be complementary to allow the protein to constantly diffuse out of the microspheres (Fig. 4). However, if the initial diffusion phase ends prior to the onset of sufficient polymer erosion to allow pore formation, the protein cannot diffuse out of the microspheres until the... 

Solutions of weak acids or bases and their conjugates exhibit buffering, the abihty to resist a change in pH following addition of strong acid or base. Since many metabohc reactions are accompanied by the release or uptake of protons, most intracellular reactions are buffered. Oxidative metabohsm produces CO2, the anhydride of carbonic acid, which if not buffered would produce severe acidosis. Maintenance of a constant pH involves buffering by phosphate, bicarbonate, and proteins, which accept or release protons to resist a change... 

Calcium ion-selective electrodes have recently been commercialized for the measurement of either total or ionized calcium Approximately 45 % of the calcium present in serum is bound to proteins, 5% is complexed to simple anions and 50% exists as the free ion. Traditionally, total calcium measurements have been made by releasing the protein bound fraction. An ion-selective electrode has now allowed the free (ionized) calcium to be measured directly. There has been much debate on the clinical significance of these measurements. The dependence of ionized calcium on pH must be considered. Samples must be either treated anaerobically, tonometered to a constant pH or have a correction factor applied. 

The number of binding sites can be determined in this model by a plot of d Ink /dlnm at constant temperature, pH, and ion valency. To do that, it may be assumed that dlny /dlnm is approximately zero. The actual value is -0.04 for 0.1 to 0.5 M sodium chloride and less at lower concentrations. To a first approximation, the stoichiometry of water molecules released by binding protein could be determined from the slope of the plot of dink /dlnm vs. m. However, especially at low salt concentration and near the isoelectric point, the slope of such plots is nonlinear. The nonlinearity may be due to hydrophobic interaction between stationary phase and protein or a large change of ionic hydration on binding.34... 

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