Protein molecules absorption

Absorption of proteins in the 230-300 nm range is determined by the aromatic side chains of tyrosine (Xmax = 274 am), tryptophan (Xmax = 280 nm), and phenylalanine (Xmax = 257 nm). Because the difference in the absorption spectra of native and unfolded protein molecules is generally small, difference spectra can... 

Hagemann et al. [3.13] calculated the absorption isotherms for recombinant bovine Somatotropin (rbSt) and found 5-8 g water in 100 g protein, which was not only on the surface but also inside the protein molecule. 

Let us now consider the retarding action of proteolytic enzymes on hydrolysis. Attention should be drawn to the fact that the carbonyl absorption band splits into two parts as a result of interaction of the cured KL-3 with proteolytic enzymes and kidney extract. Evidently it is associated with the specific interaction of the enzyme and urethane group in the polymer, the structure of which resembles the peptide group of a protein molecule. Owing to the specific action of the enzyme, this interaction does not accelerate the hydrolysis of urethane groups but even retards it owing to the shielding effect of the enzyme protein molecule. 

Hageman et al. [3.13] calculated the absorption isotherms for recombinant bovine somatotropin (rbSt) and found 5-8 g of water in 100 g of protein, which was not only on the surface but also inside the protein molecule. Costantino et al. [3.72] estimated the water monolayer M0 (g/100 g dry protein) for various pharmaceutical proteins and for their combination with 50 wt% trehalose or mannitol as excipient. They compared three methods of calculating MQ (1) theoretical (th) from the strongly water binding residues, (2) from conventional adsorption isotherm measurements (ai) and (3) from gravimetric sorption analysis (gsa) performed with a microbalance in a humidity-controlled atmosphere. Table 3.5 summarizes the results for three proteins. The methods described can be helpful for evaluating RM data in protein formulations. 

In this situation (Figure 1.3), specialized membrane protein molecules transport substrates across the cell membranes, either against the concentration gradient (active absorption), or with the concentration gradient (facilitated diffusion). 

Studies have shown that gastrointestinal mucus presents a physical barrier to the diffusion of small molecules such as urea, benzoic acid, antipyrine, 1-phenylalanine and warfarin as well as to large protein molecules. Similarly, the passive absorption of testosterone was shown to be doubled upon ridding the intestinal epithelial cells of the overlying mucus layer. However, the situation regarding the effect of mucus on oral bioavailability is a complex one for example, it has been shown that drag binding to the mucosal surface is essential to the absorption of barbituric acid derivatives from the rat small intestine. 

Since PM-IRRAS is insensitive to the strong IR absorption of water vapor, it has proved to be an efficient way to study the conformation and orientation of protein molecules because only important bands arising from the monolayer are observed [72,97-103], The first in situ study of the protein conformation by PM-IRRAS technique was reported by Dziri et al. [97]. The vibrational spectrum of acetylcholinesterase (AChE) at the air-water interface in its free form and bound to either its substrate or organophosphorus (OP) inhibitor was measured. PM-IRRAS spectra collected during compression of the AChE... 

There may be instances where one wishes to detect die absorption of molecules from a liquid into a polymeric film on the plate surface. And in biosensing, one may wish to detect the adsorption or attachment of a layer of protein molecules, cells, bacteria or other organisms on a surface. Figure 3.48 (page 130) shows an exploded view of a three-chip FPW liquid flow cell made for such applications. 

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