Protein concentration, extracellular

Figure 2. Degradation (O) of -metltylated aqueous acetone spruce wood extract ( ) in presence of concentrated extracellular P, chrysosporium culture fluid at pH 3.0 containing 0.05 gL protein with 0.2 mM H2O2 during 1 h at 37 C. Sephadex LH20/DMF elution profiles adapted and redrawn from reference 13.

Mobilization of edemas (A) In edema there is swelling of tissues due to accumulation of fluid, chiefly in the extracellular (interstitial) space. When a diuretic is given, increased renal excretion of Na and H2O causes a reduction in plasma volume with hemoconcentra-tion. As a result, plasma protein concentration rises along with oncotic pressure. As the latter operates to attract water, fluid will shift from interstitium into the capillary bed. The fluid content of tissues thus falls and the edemas recede. The decrease in plasma volume and interstitial volume means a diminution of the extracellular fluid volume (EFV). Depending on the condition, use is made of thiazides, loop diuretics, aldosterone antagonists, and osmotic diuretics. 

Extracellular Cellulolytic Activities. The appearance of the CM-cellulase activity in a culture of Thermoactinomyces grown on 1% microcrystalline cellulose is shown in Figure 2. The extracellular CM-cellulase activity approached a maximum of 14-16 mg reducing sugar (RS) mL-1 min"1 within 18-24 hr. The Avicelase activity of the culture filtrate developed simultaneously with the CM-cellulase activity and amounted to 3 mg RS mL"1 hr"1. The extracellular protein concentration reached 1.7 mg/mL in the stationary phase (6). 

It is possible to predict what happens to Vd when fu or fur changes as a result of physiological or disease processes in the body that change plasma and/or tissue protein concentrations. For example, Vd can increase with increased unbound toxicant in plasma or with a decrease in unbound toxicant tissue concentrations. The preceding equation explains why because of both plasma and tissue binding, some Vd values rarely correspond to a real volume such as plasma volume, extracellular space, or total body water. Finally interspecies differences in Vd values can be due to differences in body composition of body fat and protein, organ size, and blood flow as alluded to earlier in this section. The reader should also be aware that in addition to Vd, there are volumes of distribution that can be obtained from pharmacokinetic analysis of a given data set. These include the volume of distribution at steady state (Vd]SS), volume of the central compartment (Vc), and the volume of distribution that is operative over the elimination phase (Vd ea). The reader is advised to consult other relevant texts for a more detailed description of these parameters and when it is appropriate to use these parameters. 

It seems miraculous that a membrane about 10 nm thick can preserve extreme gradients ofintra- and extracellular ions, amino acid and protein concentration (Figure 1.1). For example, the ratio of intracellular to extracellular ion concentration for Na+ is 10 140 and for Ca2+ is 0.0001 2.5. Transmembrane concentration gradients of solvents, ions, pH, etc. are essential for cellular functions, for example the production of ATP, which cannot occur in the absence of a transmembrane gradient. 

Membranes are particularly suited for bioprocesses involving the cultivation of microorganisms or cells as biocatalysts, in which the product of interest is produced extracellularly. Such processes are becoming increasingly attractive when compared to those in which the products accumulate intracellularly. Some of the reasons for this include the use of novel expression systems which favor higher product concentrations, and the ease of purification as compared to an intracellular bioproduct route. One of the drawbacks remains that extracellular protein products are produced in dilute concentration. Extracellular-product based-processes require cell separation, product recovery and concentration. The use of ultrafiltration and microfiltration membranes has become a method of choice in such process schemes. 

Excretion of the enzyme is favorable because of cell membrane selectivity that acts as a powerful purification step, since only few proteins are excreted. Therefore, the clarified fermentation broth has a rather high degree of purity that in many cases suffices the requirements for a particular enzyme use so that further purification steps are not required. The main concern here is the low protein concentration. This represents the main drawback of extracellular enzymes, since concentration of the starting material has a profound impact on final production cost (Knight 1989). Even under dense culture conditions, protein concentration rarely exceeds a few grams per liter (Liu et al. 2000) so that the enzyme broth has to be concentrated at least by one order of magnitude prior to further purification steps or formulation. 

The most important ions for extracellular conductance by far are Na" " and Cl (Table 2.6). Note that free protein in plasma are charge carriers with a negative charge (anions) and in this context protein can be regarded as macro-ions and a conductance contributor. This charge is also the basis of DC electrophoresis as an important analytical tool in clinical chemistry (Section 2.5.1). To maintain electroneutrality, an increased protein concentration must increase the concentration of cations or reduce the concentration of other anions. The anion HCO3 is the bicarbonate related to the transport of CO2 in the blood therefore, a ehange in bicarbonate concentration (anion) will have consequences for the cation concentration. 

There are only minor differences between the electrolyte composition of plasma and the rest of the extracellular fluid. The main difference between these two fluid systems resides in the higher protein concentration in plasma. Consequently, electrolyte shifts between the two body systems follow the laws of Don-nan. Thus, the concentration of cations in the various interstitial compartments will indirectly be regulated by the amount of protein in those fluid systems, but in general, the plasma concentration of anions is higher than that of cations. 

In our model, the cell was assumed to exert traction on the ECM by transmitting the intracellular actomyosin forces to the cell surface receptors that are bound to specific proteins present in the extracellular environment. Thus, it was assumed that the cell-ECM traction was proportional to the bound receptor concentration (Cb), which is equivalent to the bound ECM protein concentration. Since it has been observed that the cell exerts more traction on stiffen substrates [11], we also assumed that this traction was proportional to the Young s modulus of the ECM ... 

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

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