Infrared spectroscopy, hydrated proteins

Wilkes et al (22.23) coupled calorimetric, dynamic-mechanical and x-ray diffraction techniques to demonstrate crystallization of the lipids was completely reversible in neonatal rat stratum corneum, and only partially reversible in human stratum corneum. Melting regions near 40°C and from 70 to 90°C corresponded to the thermal transitions noted in the calorimetric studies for both species. The crystalline nature of the lipids did not appear to be dependent on the presence of water. X-ray diffraction and infrared spectroscopy studies (23.28-34) have also shown a to p conformational changes occurred in keratin and stratum corneum protein components with hydration or exposure to increased temperatures. Oertel (28) has reported pretreatment with dimethylsulfox-ide, hexylmethylsulfoxide and decylmethylsulfoxide resulted in the formation of p-sheet protein conformations in vitro in human... 

A. Pevsner, M. Diem, Infrared Spectroscopic Studies of Major Cellular Components. Part I The Effect of Hydration on the Spectra of Proteins, Apphed Spectroscopy 55, 788, 2001. 

The development of Fourier transform infrared (FTTR) spectroscopy has facilitated the expansion ofthe scope of applications for IR spectroscopy to new fields of research, from forensics to pharmaceutical on-line analysis. The most important requirement of this technique is that the protein contain a distinctive IR-absorbing ftmctional group not present in the hydrogel. An advantage of FTIR spectroscopy is the ability to obtain spectral information for a polymer in the hydrated state, with the use of... 

To summarize, from ouf data, it can be concluded that in both LMH and LM complexes, all the protein secondary structures are oriented almost to the same extent. This observation suggests a model of the RC in which all three subunits L, M, H, have transmembrane a-helices. The observed differences between LMH and LM in the absence of nujol could be due to differences i) in the state of hydration in LMH and LM, ii) in the optical properties of the multilayers, iii) in oriented secondary structures (ex g-structure) which are removed with nujol. Similar findings were observed on other oriented air-dried membranes such as chro-matophore, thylakoid and purple membrane. We find that distortions of the amide I and amide II absorptions brought about by dehydration and/ or optical reflection effects are a general feature of protein infrared spectra. These effects are more evident in samples with small extents of dichroism (eg. air-dried samples of soluble proteins such as cytochrome c or ribonuclease) since these effects are present to the same extent, but largely hidden in samples with large dichroic signals (eg. oriented purple membrane). These results indicate that a more precise determination of membrane protein orientation by polarized IR spectroscopy requires these effects to be taken into account. 

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