Leucine complexes

A solution of the protein (0.5 mg/ml) was placed in one compartment of a dialysis chamber. An equal volume of buffer containing 4x 10" M L-leucine-C was placed in the other compartment. The compartments are separated by a semipermeable membrane through which the labeled amino acid can move freely. The protein, however, is restricted to one compartment. After equilibration, the compartment containing the protein had 2.3x10 total (bound 4-free) L-leucine-C. The compartment without protein contained 1,7 X 10 M Ldeucine-C. Calculate (a) the concentration of bound L-leudne-C [PS] or [S]i, (b) the concentration of free protein, [P]/, and (c) the dissociation constant for the protein-leucine complex assuming one bindir site per molecule of protein. 

An amino acid binding protein (MW = 35,000) was purified from E. colt. A solution of the protein (0.5 mg/ml) was placed in one compartment (O.lO ml) of an equilibrium dialysis chamber (the plus compartment). A solution of L-leucine-C (S,A. = 2 X lO CPM/zimole) was placed in the other ( minus ) compartment (0.10 ml). At equilibrium, lO/il of solution from the plus compartment contained 4600 CPM. Ten microliters of solution from the minus compartment contained 3400 CPM. Calculate the concentration of bound L-leucine-C , and the Ks for the protein-leucine complex. Assume one binding site per protein molecule. 

Besides the routine stereoselective analysis, low cost and simplicity of CE and CEC methods make them popular tools for fast screening of chiral selectors [112], for studying mechanisms of discrimination, or for determining the binding constant, as it has been shown for t-BuCQN and (S)-DNB-leucine complex [113]. 

Ellenberger, T.E., et al. The GCN4 basic region leucine zipper binds DNA as a dimer of uninterrupted a helices crystal structure of the protein-DNA complex. Cell 71 1223-1237, 1992. 

Activator Protein-1 (API) comprises transcriptional complexes formed by dimers of members oftheFos, Jun, and ATF family of transcription factors. These proteins contain basic leucine zipper domains that mediate DNA binding and dimerization. They regulate many aspects of cell physiology in response to environmental changes. 

The von Willebrand factor (vWf) is a heterogeneous multimeric plasma glycoprotein produced by megakaryocytes and endothelial cells which is found in platelets, plasma and the subendothelium. Subendothelial vWf facilitates platelet adhesion, especially under high shear stress, by binding to glycoprotein GPIb-V-IX, a complex of four leucine-rich repeat proteins on platelets. 

PhsSnflV)] complexes of N-Ac-Gly, Af-acetyl-leucine, N-acetyl-asparagine, and N-Ac-L-Tyr were prepared by two procedures and characterized by means... 

As the name implies, the odor of urine in maple syrup urine disease (brancbed-chain ketonuria) suggests maple symp or burnt sugar. The biochemical defect involves the a-keto acid decarboxylase complex (reaction 2, Figure 30-19). Plasma and urinary levels of leucine, isoleucine, valine, a-keto acids, and a-hydroxy acids (reduced a-keto acids) are elevated. The mechanism of toxicity is unknown. Early diagnosis, especially prior to 1 week of age, employs enzymatic analysis. Prompt replacement of dietary protein by an amino acid mixture that lacks leucine, isoleucine, and valine averts brain damage and early mortality. 

In polar solvents, the structure of the acridine 13 involves some zwitterionic character 13 a [Eq. (7)] and the interior of the cleft becomes an intensely polar microenvironment. On the periphery of the molecule a heavy lipophilic coating is provided by the hydrocarbon skeleton and methyl groups. A third domain, the large, flat aromatic surface is exposed by the acridine spacer unit. This unusual combination of ionic, hydrophobic and stacking opportunities endows these molecules with the ability to interact with the zwitterionic forms of amino acids which exist at neutral pH 24). For example, the acridine diacids can extract zwitterionic phenylalanine from water into chloroform, andNMR evidence indicates the formation of 2 1 complexes 39 such as were previously described for other P-phenyl-ethylammonium salts. Similar behavior is seen with tryptophan 40 and tyrosine methyl ether 41. The structures lacking well-placed aromatics such as leucine or methionine are not extracted to measureable degrees under these conditions. 

Alanine, valine, and leucine, (amino-acids with alkyl substituents only) react in a manner very like that of glycine (49—53). All the reactions are rather slow and boiling solutions are normally employed in the preparative reactions. With the cis- and /raws-isomers of Pt(NHs)2Cl2 substitution of the chloride only occurs. Since the tfraws-labilising influence of the incoming groups of the amino-acids is very small, the —NH2 groups remain stable. Consequently chelated complexes are only formed by the amino-acids in the case of the cts-isomer. 

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