Hemoglobin conformational dynamics

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

Even though in vitro experiments necessarily remove biomolecules from the cellular environment, the structures and dynamics of individual macromolecules provide insights to their biological functions. For example, structural studies have revealed that the protein hemoglobin is made up of four interacting subunits, two a subunits and two ft subunits. Furthermore, each subunit has two distinct conformational states, called the R state and the T state, and the energy of interaction between two neighboring subunits in different states is different from that of two subunits in the same state. This phenomenon is the structural basis of the observed allosteric... 

Szabo, A. G., Krajcarski, D., Zuker, M. and Alpert, B, 1984, Conformational heterogeneity in hemoglobin as determined by picosecond fluorescence decay measurements of the tryptophan residues. Chemical Physical letters. 108, 145-149. Swaminathan, R., Nath, U., Udgaonkar, J. B., Periasamy, N. and Krishnamoorthy, G. 1996, Motional Dynamics of a Buried Tryptophan Reveals the Presence of Partially Structured Forms during Denaturation of Barstar. Biochemistry 35, 9150 -9157. Tadokoro, H. in Structure of Crystalline Polymers, John Wiley and Sons, New York, 1979. 

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