Amino terminal

Fig. 2. Schematic of the G-proteia coupled receptor (GPCR). The seven a-heUcal hydrophobic regions spanning the membrane are joined by extraceUular and iatraceUular loops. The amino terminal is located extraceUulady and the carboxy terminal iatraceUulady.

Several enzymes, none of which are completely specific for the enkephalins, are known to cleave Leu- and Met-enkephalin at various peptide bonds. The main enzymes that degrade enkephalin are 2inc metaHopeptidases. The first enkephalin-degrading enzyme to be identified, an aminopeptidase which cleaves the amino terminal Tyr-Gly bond (179), has been shown to be aminopeptidase-N (APN) (180). It is a cytoplasmic enzyme which is uniformly distributed throughout the brain. The increased analgesic activity of synthetic enkephalins substituted by D-amino acids at position 2, eg,... 

A two-site immunometric assay of undecapeptide substance P (SP) has been developed. This assay is based on the use of two different antibodies specifically directed against the N- and C-terminal parts of the peptide (95). Affinity-purified polyclonal antibodies raised against the six amino-terminal residues of the molecule were used as capture antibodies. A monoclonal antibody directed against the carboxy terminal part of substance P (SP), covalently coupled to the enzyme acetylcholinesterase, was used as the tracer antibody. The assay is very sensitive, having a detection limit close to 3 pg/mL. The assay is fiiUy specific for SP because cross-reactivity coefficients between 0.01% were observed with other tachykinins, SP derivatives, and SP fragments. The assay can be used to measure the SP content of rat brain extracts. 

C rb myl tion. Modification of the amino-terminal groups of hemoglobin (Hb) by the carbamylation reaction using isocyanic acid [75-13-8]... 

Bis-Pyndoxal Tetraphosphate. A second class of bifunctional reagents, described in 1988, involves two pyridoxal groups linked by phosphates of different lengths (89). As shown in Table 4, the yield of intramolecularly cross-linked hemoglobin increases dramatically with increasing length of the phosphate backbone. It is beheved that the site of reaction of (bis-PL) is between the amino-terminal amino group of one P-chain and the... 

Sequences have been determined for plasminogen and bovine Factor XII, and they are not homologous with the other serine proteases. The amino-terminal sequence of Factor XII is homologous, however, with the active site of several naturally occurring protease inhibitors (11). 

Other backbone stmctures that have generated a great interest are the polyether ketones. An attempt was made to synthesize amino-terminated arylene ether ketones, which were subsequendy converted into the corresponding maleinhde-terrninated oligomers (26). The aim of this approach was to obtain tough, solvent-resistant, high temperature thermosets. 

The common synthetic route to bismaleimides or maleimide functionalized oligomers is the condensation of diamines or amino-terminated oligomers with maleic anhydride. Another possibiUty is the use of an AB-type monomer of the following general formula to build the polymaleimide, where X represents a functional group that can be employed in condensation reactions. 

Entry Carboxy terminal Amino terminal Product Enzyme Solvent Yield, % Refs... 

The major stmctural feature of the HAz chain (blue in Figure 5.20) is a hairpin loop of two a helices packed together. The second a helix is 50 amino acids long and reaches back 76 A toward the membrane. At the bottom of the stem there is a i sheet of five antiparallel strands. The central i strand is from HAi, and this is flanked on both sides by hairpin loops from HAz. About 20 residues at the amino terminal end of HAz are associated with the activity by which the vims penetrates the host cell membrane to initiate infection. This region, which is quite hydrophobic, is called the fusion peptide. 

CDK2 has two domains, a small (85 residue) amino-terminal domain comprising a single a helix and a five-stranded p sheet and a larger (213 residues) domain that is mainly a-helical (Figure 6.17a). The cofactor in the... 

Figure 8.21 Richardson-type diagram of the structure of one suhunit of the lac repressor. The polypeptide chain is arranged in four domains, an amino terminal DNA-hinding domain (red) with a helix-tum-helix motif, a hinge helix (purple), a large core domain which has two subdomains (green and hlue) and a C-terminal a helix. (Adapted from M. Lewis et al.. Science 271 1247-1254, 1996.)...

Mondragon, A., et al. Structure of the amino-terminal domain of phage 434 repressor at 2.0 A resolution. 

Figure 14.5 The domain organization of intermediate filament protein monomers. Most intermediate filament proteins share a similar rod domain that is usually about 310 amino acids long and forms an extended a helix. The amino-terminal and carboxy-terminal domains are non-a-helical and vary greatly in size and sequence in different intermediate filaments.

The most remarkable feature of the antibody molecule is revealed by comparing the amino acid sequences from many different immunoglobulin IgG molecules. This comparison shows that between different IgGs the amino-terminal domain of each polypeptide chain is highly variable, whereas the remaining domains have constant sequences. A light chain is thus built up from one amino-terminal variable domain (Vl) and one carboxy-terminal constant domain (Cl), and a heavy chain from one amino-terminal variable domain (Vh), followed by three constant domains (Chi, Ch2. and Chs). 

Amino acid analysis itself does not directly give the number of residues of each amino acid in a polypeptide, but it does give amounts from which the percentages or ratios of the various amino acids can be obtained (Table 5.2). If the molecular weight and the exact amount of the protein analyzed are known (or the number of amino acid residues per molecule is known), the molar ratios of amino acids in the protein can be calculated. Amino acid analysis provides no information on the order or sequence of amino acid residues in the polypeptide chain. Because the polypeptide chain is unbranched, it has only two ends, an amino-terminal or N-terminal end and a carboxyl-terminal or C-termuial end. 

According to Charbonneau et al. (1985), aequorin is a single chain peptide consisting of 189 amino acid residues, with an unblocked amino terminal. The molecule contains three cysteine residues and three EF-hand Ca2+-binding domains. The absorption spectra of aequorin and BFP are shown in Fig. 4.1.3, together with the luminescence spectrum of aequorin and the fluorescence spectrum of BFP. 

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