Proteins in blood plasma

When most lipids circulate in the body, they do so in the form of lipoprotein complexes. Simple, unesterified fatty acids are merely bound to serum albumin and other proteins in blood plasma, but phospholipids, triacylglycerols, cholesterol, and cholesterol esters are all transported in the form of lipoproteins. At various sites in the body, lipoproteins interact with specific receptors and enzymes that transfer or modify their lipid cargoes. It is now customary to classify lipoproteins according to their densities (Table 25.1). The densities are... 

Some dmgs are bound to plasma proteins in blood. Plasma protein levels in blood may be decreased in the elderly, but this is most often not clinically relevant since a drug s elimination increases when the free, unbound drug concentration is enhanced (Turnheim 1998). The plasma albumin level may however be markedly decreased in elderly suffering from malnutrition or severe disease. For those patients the concentration of the free unbound drug can reach toxic levels (Waiter-Sack and Klotz 1996). 

Serum albumin is the most abundant protein in blood plasma. Its primary function is to control the colloidal osmotic pressure in blood, but is also important for its buffering capacity and for its ability to transport fatty acids and bilirubin, as well as xenobiotic molecules. The physiological implications of its esterase-like activity are unknown (see Sect. 3.7.5). 

Several mechanisms have evolved to prevent this catastrophe. In bacteria and plants, the plasma membrane is surrounded by a nonexpandable cell wall of sufficient rigidity and strength to resist osmotic pressure and prevent osmotic lysis. Certain freshwater protists that live in a highly hypotonic medium have an organelle (contractile vacuole) that pumps water out of the cell. In multicellular animals, blood plasma and interstitial fluid (the extracellular fluid of tissues) are maintained at an osmolarity close to that of the cytosol. The high concentration of albumin and other proteins in blood plasma contributes to its osmolarity. Cells also actively pump out ions such as Na+ into the interstitial fluid to stay in osmotic balance with their surroundings. 

Table 4 Percentage Occurrence of the Major Complexes (Non-protein) in Blood Plasma from Computer Simulation -1 ...

Serum albumin is the most plentiful protein in blood plasma. Each molecule can carry seven fatty acid molecules. They bind in deep crevices in the protein, burying their carbon-rich chains away from the surrounding water. Serum albumin also binds to many other water-insoluble molecules. In particular, serum albumin binds to many drug molecules and can strongly affect the way they are delivered through the body. 

MRI CAs meet a variety of biomolecules in physiological environments, and may interact with proteins, human serum albumin (HSA), enzymes, and receptors. The binding of CAs to HSA is widely studied because it is the most abundant protein in blood plasma. HSA has a molecular weight of 66 kDa, a concentration of approximately 0.64 mM, and with two major binding sites, which are subdomains of IIA and III A [63]. 

Selenoprotein P. This protein is the major selenium-containing protein in blood plasma, may be a transport protein for the element, and has an antioxidant function. ... 

Salt, H. B., Micro analytical methods for proteins in blood plasma. Analyst 78, 4-14 (1953). 

For a long time erythrocuprein was thought to act exclusively as a copper-transporting protein. This was a very attractive conclusion since over 50% of the erythrocyte copper content is present in erythrocuprein (60). However, in the absence of any known function of a metalloprotein, it is always tempting to assign to it the role of storage or transport of the respective metal ions. For example, caeruloplasmin was considered to be the main copper-transporting protein in blood plasma. It subsequently turned out that this copper protein is a key enzyme in iron metabolism, responsible for the oxidation of Fe2+ to the Fe3+ bound in transferrin (130—132). 

The concentration of proteins in blood plasma is 60 mg mL . In order to minimize any contribution to the signal by dissolved species [743], the ATR measurements are conducted in very dilute protein solutions ( 1 mg mL ). However, this is not the case with coated ATR, where the thickness of the thin-film substrate controls the penetration depth (see Section 4.1.3 for more detail). For example, at a solution concentration of 60 mg mL and under the optical conditions of 45° Ge MIRE coated with a 0.4-p,m-thick polymer coating, the contribution of the bulk solution was estimated to be 0.47% of the total spectra [769]. When it is necessary to follow adsorption at higher protein concentrations, special cells and measurement protocols based on internal standards are used for correcting for the bulk protein signal, which are discussed in detail by Jakobsen and Strand [743],... 

When a medical device is in contact with body fluid such as blood, the first thing that occurs on the surface is protein adsorption [96-98]. Proteins in solution trying to minimize the total surface energy is the thermodynamic driving force of protein adsorption on solid surfaces. In blood contact protein adsorption is believed to be the initial event in thrombus formation [99-101], calcification [102-104], and biofilm attachment [105-107], which leads to the failure of implanted devices. Therefore, protein-reducing surface modifications of polyurethane biomaterials have been applied to improve the service life of implants. Previous studies of protein adsorption have focused on adsorption of albumin, IgG, and Fg, which are the predominant three proteins in blood plasma. Surface protein adsorption can be quantitated by several methods such as quartz crystal microbalance (QCM) [108-112], surface plasmon resonance (SPR) [113-118], and iodonization radiolabeling [78,119-125]. 

As indicated in Section I, the apparent mobility of a component under standardized experimental conditions is determined not only by the properties, concentration, and environment of that component but is also a function of the mobilities and concentrations of all the other components of the system. Thus the mobility of a Bence-Jones protein in urine may differ somewhat from that of the same Bence-Jones protein in blood plasma. Experiments in which urinary Bence-Jones proteins were added to normal serum, to be described, show that such environmental factors are probably responsible for the differences observed. 

Ser2oThr2iTyT (HjO) . These formulas will require some modification but they appear to be suflSciently accurate to give the most concrete version yet available of the structure of a simple protein. The proteins in blood plasma are of higher molecular weight, some over 1,000,000 moreover many are in combination or association with complex lipides and/or carbohydrates, which in themselves offer countless possibilities for further variation in composition. 

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