Amino acids hydrophilic nature

Host defense peptide hydrophobicity (H) is defined as the proportion of hydrophobic amino acids within a peptide. Typically, these peptides are comprised of >30% hydrophobic residues and this governs the ability of a host defense peptide to partition into the lipid bilayer, an essential requirement for antimicrobial peptide-membrane interactions. Typically, the hydrophobic and hydrophilic amino acids of natural peptides are segregated to create specific regions or domains that allow for optimal interaction with microbial membranes. This likely represents evolutionary optimization to maximize the selectivity of these defense molecules. It has been established that increasing antimicrobial peptide hydrophobicity above a specific threshold correlates... 

The 20 natural amino acids differ from each other by the nature of their sidechains. Differences involve overall size, hydrophobic or hydrophilic character and, perhaps most importantly, ionization state. While the sidechains are normally written in terms of neutral structures, some may also exist in either protonated or deprotonated forms depending on pH. 

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

Tyrosine contains a phenolic side chain with a pKa of about 9.7-10.1. Due to its aromatic character, tyrosine is second only to tryptophan in contributing to a protein s overall absorptivity at 275-280nm. Although the amino acid is only sparingly soluble in water, the ionizable nature of the phenolic group makes it often appear in hydrophilic regions of a protein—usually... 

Simple organic molecules such as small carboxylic acids (oxalate, acetate, malonate, citrate, etc.), amino acids and phenols are all ligands for metals. Such compounds may all occur as degradation products of organic matter in natural waters. The complexes formed are typically charged hydrophilic complexes. The stability of the metal complexes with these ligands is, however, moderate in most cases. Model calculations including such compounds at realistic concentrations indicate that their effects on speciation are relatively small [29],... 

The C-terminal region must be predominantly hydrophobic, as increasing the hydrophobic nature by amino acid substitution slightly increases the histamine-releasing activity, while increasing the hydrophilic nature of the C-terminal decreases histamine-releasing activity [99, 169, 170-176]. 

Noncovalent interactions play a key role in biodisciplines. A celebrated example is the secondary structure of proteins. The 20 natural amino acids are each characterized by different structures with more or less acidic or basic, hydrophilic or hydrophobic functionalities and thus capable of different intermolecular interactions. Due to the formation of hydrogen bonds between nearby C=0 and N-H groups, protein polypeptide backbones can be twisted into a-helixes, even in the gas phase in the absence of any solvent." A protein function is determined more directly by its three-dimensional structure and dynamics than by its sequence of amino acids. Three-dimensional structures are strongly influenced by weak non-covalent interactions between side functionalities, but the central importance of these weak interactions is by no means limited to structural effects. Life relies on biological specificity, which arises from the fact that individual biomolecules communicate through non-covalent interactions." " Molecular and chiral recognition rely on... 

If the virus is treated with proteolytic enzymes the fuzzy layer formed by the viral spikes is removed (Osterrieth, 1965 Compans, 1971 Gahm-berg et al, 1972 Sefton and Gaffney, 1974 Utermann and Simons, 1974). Remnants of both El and E2 are left in the bilayer. These have a hydrophobic amino acid composition, and are soluble in lipid solvents such as chloroform-methanol. The amphiphilic nature of the spike protein is also evident from its capacity to bind Triton X-100 (0.6 g/g protein) which binds to the hydrophobic part to form a water-soluble protein-detergent complex (Simons et al., 1973a). The ability of amphiphilic proteins to bind Triton can be used to separate them from hydrophilic proteins using an extraction procedure recendy described... 

We are now in a position to nnderstand the molecnlar nature of sickle cell anemia. We need to remember that amino acids come in three flavors nonpolar, charged (highly hydrophilic polar), and uncharged polar. We also need to remember that proteins are organized in a way that hides most of the nonpolar amino acid residues in the molecular interior and exposes most of the charged, in particular, and uncharged polar residues on the molecnlar snrface. 

This chapter aims to summarize our efforts to investigate the effects of fluorinated amino acid substitutes on the interactions with natural protein environments. In addition to a rather specific example concerning the interactions of small peptides with a proteolytic enzyme, we present a simple polypeptide model that aids for a systematic investigation of the interaction pattern of amino acids that differ in side chain length as well as fluorine content within both a hydrophobic and hydrophilic protein environment. Amino acid side chain fluoiination highly affects polypeptide folding due to steric effects, polarization, and fluorous interactions. 

The ionic and hydrophilic nature of the amino acids precludes their isolation from biological fluids by solvent/solvent extraction. Modification of the amino group, for example the formation of an N-acetyl group, makes solvent extraction accessible. 

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