Amino acids basic

The positively charged guanidinium group attached to the S-carbon of arginine is stabilized by resonance between the two NH2 groups and has a pK value of 12.48. Arginine is utilized in the synthesis of creatine and it participates in the urea cycle (Chapter 17). 

The nitrogen of the guanidino group of arginine is converted to nitric oxide (NO) by nitric oxide synthase. NO is unstable, highly reactive, and has a life span of only a few seconds. However, NO affects many biological activities, including vasodilation, inflammation, and neurotransmission (Chapter 17). 

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CfiHqNaO . M.p. 277 C. The naturally occurring substance is laevorotatory. Histidine is one of the basic amino-acids occurring in the hydrolysis products of proteins, and particularly of the basic proteins, the protamines and histones. It is an essential constituent of the food of animals. 

H2N-CH2 [CH2j3.CH(NH2) COOH. Colourless needles, m.p. 224 C (decomp.), very soluble in water, insoluble in alcohol. L-(-H)-Lysine is one of the basic amino-acids occurring in particularly large quantities in the protamine and histone classes of proteins. It is an essential amino-acid, which cannot be synthesized by the body and must be present in the food for proper growth. It can be manufactured by various fermentation processes or by synthesis. 

Fig. 1. Schematic drawing of precursors for selected brain oligopeptides. Shaded areas represent the location of sequences of active peptide products which are normally cleaved by trypsin-like enzymes acting on double-basic amino acid residues. Precursors are not necessarily drawn to scale, (a) CRF precursor (b) proopiomelanocortin (POMC) (c) P-protachykinin (d) proenkephalin A (e) CGRP precursor (f) preprodynorphin, ie, preproenkephalin B. Terms are...

Biosynthesis. Two closely related genes encode the three mammalian tachykinins. The preprotachykinin A gene encodes both substance P and substance K, while the preprotachykinin B gene encodes neuromedin K (45—47). The active sequences are flanked by the usual double-basic amino acid residues, and the carboxy-terrninal amino acid is a glycine residue which is decarboxylated to an amide. As with most neuropeptide precursors, intermediates in peptide processing can be detected, but their biological activities are not clear (ca 1994). 

Biosynthesis. CRE is derived from a precursor of 196 amino acids (84,85). This gene contains one copy of CRE, which is flanked by double basic amino acids. The amino acid sequence of the CRE precursor suggests that it may arise from proteins related to POMC and neurophysins (31). The CRE precursor contains a cAMP responsive element which aHows stimulation of mRNA synthesis when intraceHular levels of cAMP are increased (86). 

CGRP has a wide distribution in the nervous system (19) and was the first peptide to be localized to motoneurons (124). It is also found in primary sensory neurons where it is colocalized with substance P (125). CGRP is derived from a precursor stmcturaHy related to the calcitonin precursor. The latter precursor produces two products, calcitonin itself and katacalcin, while the CGRP precursor produces one copy of CGRP (123). Like other peptides, CGRP is cleaved from its precursor by tryptic breakdown between double basic amino acid residues. 

The history of the discovery of amino acids is closely related to advances ia analytical methods. Initially, quantitative and qualitative analysis depended exclusively upon crystallization from proteia hydrolysates. The quantitative precipitation of several basic amino acids including phosphotungstates, the separation of amino acid esters by vacuum distillation, and precipitation by sulfonic acid derivatives were developed successively duriag the last century. 

Ben2enesulfonate compounds yield very iasoluble salts which have been used for separation and identification of amino acids (89). Similarly, phosphotungstic acid forms iasoluble salts with basic amino acids such as lysiae, arginine, and cysteiae. 

The coiled-coil structure of the leucine zipper motif is not the only way that homodimers and heterodimers of transcription factors are formed. As we saw in Chapter 3 when discussing the RNA-binding protein ROP, the formation of a four-helix bundle structure is also a way to achieve dimerization, and the helix-loop-helix (HLH) family of transcription factors dimerize in this manner. In these proteins, the helix-loop-helix region is preceded by a sequence of basic amino acids that provide the DNA-binding site (Figure 10.23), and... 

Amino acids with basic side chains Basic amino acids are the opposite of acidic... 

Some amino acids have side chains that bear- acidic or basic groups. As Table 27.3 indicates, these amino acids are characterized by three pK values. The third pK reflects the nature of the side chain. Acidic amino acids (aspartic and glutfflnic acid) have acidic side chains basic amino acids (lysine, arginine, and histidine) have basic side chains. 

The isoelectric point of an amino acid depends on its structure, with values for the 20 common amino acids given in Table 26.1. The 15 neutral amino acids have isoelectric points near neutrality, in the pH range 5.0 to 6.5. The two acidic amino acids have isoelectric points at lower pH so that deprotonation of the side-chain -C02H does not occur at their pi, and the three basic amino acids, have isoelectric points at higher pH so that protonation of the side-chain amino group does not occur at their pi. 

Just as individual amino acids have isoelectric points, proteins have an overall p/ because of the acidic or basic amino acids they may contain. The enzyme lysozyme, for instance, has a preponderance of basic amino acids and thus has a high isoelectric point (p/= 11.0). Pepsin, however, has a preponderance of acidic amino acids and a low- isoelectric point pi 1.0). Not surprisingly, the solubilities and properties of proteins with different pi s are strongly affected by the pH of the medium. Solubility- is usually lowest at the isoelectric point, where the protein has no net charge, and is higher both above and below the pi, where the protein is charged. 

Partial hydrolysis of a peptide can be carried out either chemically with aqueous acid or enzymatically. Acidic hydrolysis is unselective and leads to a more or less random mixture of small fragments, but enzymatic hydrolysis is quite specific. The enzyme trypsin, for instance, catalyzes hydrolysis of peptides only at the carboxyl side of the basic amino acids arginine and lysine chymotrypsin cleaves only at the carboxyl side of the aryl-substituted amino acids phenylalanine, tyrosine, and tryptophan. 

What about tertiary structure Why does any protein adopt the shape it does The forces that determine the tertiary structure of a protein are the same forces that act on ail molecules, regardless of size, to provide maximum stability. Particularly important are the hydrophilic (water-loving Section 2.13) interactions of the polar side chains on acidic or basic amino acids. Those acidic or basic amino acids with charged side chains tend to congregate on the exterior of the protein, where they can be solvated by water. Those amino acids with neutral, nonpolar side chains tend to congregate on the hydrocarbon-like interior of a protein molecule, away from the aqueous medium. 

A more complete characterization of proteins was proposed in 1899 by Hausmann (130), who determined the distribution of nitrogen among amides, the basic amino acids,... 

Furin, also known as paired basic amino-acid-cleaving enzyme (PACE), is a membrane bound subtilisin-like serine protease of the irons Golgi compartment. It is ubiquitously expressed and mediates processing of many protein precursors at Arg-X-Lys/Arg-Arg sites. 

Histone proteins share distinct features including a high content of basic amino acids, lysines and arginines,... 

US4515 804 (Zyma 7.5.1985 GB-prior. 24.2.1982). salts with basic amino acids ... 

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