Amino acids positively charged

The first DAAO studied mechanistically was from pig kidney (pkDAAO) many kinetic and mechanistic studies have been performed on this enzyme. More recently, yeast DAAOs from Rhodotorula gracilis (RgDAAO) and Trigonopsis variabilis (TvDAAO) have also been studied. Each has different substrate specificities. The best substrate for pkDAAO is D-proline, followed by hydrophobic and neutral amino acids. Positively charged amino acids are bad substrates, while negatively charged D-amino acids are not substrates.In contrast, methionine and valine are the best substrates for RgDAAO. ... 

Despite the variety of different sources, sequences and structures, all cationic antimicrobial peptides share some common features small size (12-50 amino acids), positive net charge (+2 to +9), amphiphilic (>30% hydrophobic amino acids) and antimicrobial and/or immunomodulatory activity. Some cationic antimicrobial peptides also show antiviral (14) and/or anticancer activity (15) as well as wound healing properties (16). More than 1000... 

Acidic polysaccharides (see Table IV) that contain uronic acid residues are, perhaps, the most prevalent type of exocellular polysaccharide. Often, these acidic biopolymers contain other sugars, including pentoses, hexoses, and heptoses, also found in neutral polysaccharides (see Tables V and VI). In many instances, these polymers possess alkali-labile O-acyl substituents, such as acetic, formic, ma-lonic, pyruvic, and succinic acids. Positively charged biopolymers that contain free amino sugars are rare, but have been found (see Table VII). More often, these amino sugars are N-acylated, generally with acetyl groups. 

FIGURE 6.32 Apolipoprotein E. A silhouette of the apo E molecule is shown. The amino acid positions that have been found to be altered genetically in patients with cardiovascular diseases are highlighted and numbered. All the highlighted amino adds aie positively charged and occur at the apo E binding site, that is, that portion of the molecule tecognifed by an apo E receptor. (Redrawn with permission from Innerarity ei al., 1984.)... 

Purification of a protein is indispensable for establishing its amino acid sequence. Mixtures of proteins will yield mixtures of peptides and ambiguous amino acid positions a unique amino acid sequence can be obtained only from a pure protein. Protein purification techniques exploit differences in size, shape, charge, solubility, and specific binding affinity of the proteins. The optimal combination of techniques is usually reached by trial and error. 

The protein isoelectric point (pi) value is the pH at which the sum of acidic amino-add negative charges and of basic amino-add positive charges equals zero. It ranges between less than 3 and more than 12. 

At the surfaces of proteins are amino acid residues that interact with water. The amino acids are referred to as hydrophilic amino acids and include arginine, lysine, aspartic acid, and glutamic acid. At pH 7 the side chains of these amino acids carry charges—positive for arginine and lysine, negative... 

Fig. 5.HYDROPATHY PLOTS OF THE DERIVED X GENE PEPTIDES. The R. sphaeroides (dotted line or arrows) and R. capsulatus (solid line or arrows) X protein hydropathy plots were generated using the mean of 11 amino acids. Positively and negatively charged residues are indicated by arrows pointing upwards and downwards, respectively. The dotted line across the figure indicates the average energies for each peptide and all parts below this line are considered hydrophobic.

Lysine is a basic amino acid with two amino groups (positively charged at pH 6-7) and one carboxyl group with a chemical name cqe-diamino caproic acid. 

Scheme 1 Low-energy structures for the complex of and Trp. Structures can be classified as salt-bridge (SB interaction between the positive metal ion and the negative carboxylate of the zwitterionic amino acid) or charge solvation (CS interaction of the metal ion with Lewis-basic sites of the canonical amino acid). Nomenclature of the various structures further includes the main binding sites of the amino acid...

Some proteins are subject to the C-terminal rule which predicts that proteins having a C-terminal stretch comprised predominantly of a PEST (Pro, Glu, Ser, and Thr) sequence motif are rapidly degraded (41). For example, ornithine decarboxylase containing the C-terminal PEST sequence has a half-life at least four times shorter than the same protein without the PEST motif (42). The PEST rule is subject to the polarity of the terminal residues nonpolar amino acids are destabilizing when placed at the five amino acid positions of the C terminus, whereas charged and polar residues are stabilizing (43). 

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