Amino acid protolytic

The amino acids are ampholytes, having both acid and basic properties. Their protolytic properties are best described by values (or pAg values), macroscopic dissociation constants for the acid groups involved. In Table II pA values are given for all the protein amino acids. The pAg values listed... 

The protolytic properties of amino acids determine their behavior towards ion-exchange resins when these are employed for both analytical and preparative purposes. 

The position of the equilibrium is pH dependent because of the protolytic properties of the molecules involved, the amino acid, the carbon dioxide carbonic acid hydrogen carbonate carbonate system, and the car-baminic acid. At low and at very high pH values only negligible amounts of carbaminates will be present in equilibrium with amino acids and the carbonate system. The C-nmr investigations have shown that the highest fraction of carbaminate present in equilibrium with glycine and the carbonate system... 

The complexes of neutral amino acids have therefore net cheu ge zero and are normally only slightly soluble. The corresponding complexes of acidic and basic amino acids, on the other hand, have charges different from zero in a large part of the pH region because of the protolytically active groups in the side chains. 

The behavior of the amino acids in aqueous solution is determined mainly by the principal functional groups, the a-amino group and the a-carboxyl group. Side chains with protolytically active groups, however, determine the division into acidic, neutral, and basic amino acids. 

Light-induced electron transport in bacterial photosynthetic reaction centers leads to the creation of a charge-separated state stable for milliseconds to seconds. The structures provided by X-ray crystallography (Michel et aL, 1986 Allen et al., 1988 Deisenhofer Michel, 1989 El-Kabbani et al., 1991) constitute a unique guideline to address questions on how the function may be related to the arrangement of the cofactors and of specific amino acid residues in their vicinity. The sequence of electron transfer reactions, the identity of the reaction partners, and the reaction mechanisms have been characterized from static and time-resolved absorbance measurements (for a review, see Parson Ke, 1982). Transfer of the first electron to the primary (Q ) and secondary (Qg) quinone electron acceptors has received considerable attention, since it is associated with intraprotein protolytic reactions (for a recent review, see Okamura Feher, 1992), which have a potential role in electrostatic charge stabilization. 

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