Enzymes amino acid sequence

ExPASy (Expert Protein Analysis System, www.expasy.ch) or the National Centre for Biotechnology Information (NCBI, www.ncbi.nlm.gov) websites. Both websites provide bioinformatics tools, links to sequence databases and extensive bibliographic resources. As an example of the wealth of information available on individual enzymes, at the time of writing a search based on nitrilase in the Entrez protein section of NCBI will recover more than 10000 references to nitrilase enzyme amino acid sequences. These can be rapidly screened online by organism, and the individual entries will have links to amino acid and gene sequence, relevant literature and information on protein features (such as conserved domains). 

Source Enzyme Amino acid sequence IC50 (pM) Reference... 

Proenzyme heptapeptide-enzyme Amino acid sequence known Six S—S bridges... 

Firefly. Firefly luciferase (EC 1.13.12.7) is a homodimeric enzyme (62 kDa subunit) that has binding sites for firefly luciferin and Mg ATP . Amino acid sequence analysis has iadicated that beetle luciferases evolved from coen2yme A synthetase (206). Firefly bioluminescence is the most efficient bioluminescent reaction known, with Qc reported to be 88% (5), and at 562 nm (56). At low pH and ia the presence of certain metal ions (eg, Pb ", ... 

Proteins are macromolecules that play many roles such as serving as enzymes or components of cell membranes and muscle. The antibodies that protect against invasion by foreign substances are themselves proteins. There are twenty-odd amino acids found regularly in most naturally occurring proteins. Because of the great length of protein chains and the various sequences of amino acids, the theoretic number of possible proteins is astronomical. The amino acid sequence is referred to as the primaiy structure of a protein. The pol eptide... 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

The eight-stranded a/p-barrel stmcture is one of the largest and most regular of all domain stmctures. A minimum of about 200 residues are required to form this structure. It has been found in many different proteins, most of which are enzymes, with completely different amino acid sequences and... 

In Bacillus snbtilis these two reactions are catalyzed by two separate enzymes that have amino acid sequences homologous to the corresponding regions of the bifunctional enzyme from E. coli, and thus each forms a barrel... 

The a/p-barrel structure is one of the largest and most regular of all domain structures, comprising about 250 amino acids. It has so far been found in more than 20 different proteins, with completely different amino acid sequences and different functions. They are all enzymes that are modeled on this common scaffold of eight parallel p strands surrounded by eight a helices. They all have their active sites in very similar positions, at the bottom of a funnel-shaped pocket created by the loops that connect the carboxy end of the p strands with the amino end of the a helices. The specific enzymatic activity is, in each case, determined by the lengths and amino acid sequences of these loop regions which do not contribute to the stability of the fold. 

Most of the known antiparallel p structures, including the immunoglobulins and a number of different enzymes, have barrels that comprise at least one Greek key motif. An example is 7 crystallin, which has two consecutive Greek key motifs in each of two barrel domains. These four motifs are homologous in terms of both their three-dimensional structure and amino acid sequence and are thus evolutionarily related. 

The enzyme provides a general base, a His residue, that can accept the proton from the hydroxyl group of the reactive Ser thus facilitating formation of the covalent tetrahedral transition state. This His residue is part of a catalytic triad consisting of three side chains from Asp, His, and Ser, tvhich are close to each other in the active site, although they are far apart in the amino acid sequence of the polypeptide chain (Figure 11.6). 

Even though these enzymes have no absolute specificity, many of them show a preference for a particular side chain before the scissile bond as seen from the amino end of the polypeptide chain. The preference of chymotrypsin to cleave after large aromatic side chains and of trypsin to cleave after Lys or Arg side chains is exploited when these enzymes are used to produce peptides suitable for amino acid sequence determination and fingerprinting. In each case, the preferred side chain is oriented so as to fit into a pocket of the enzyme called the specificity pocket. 

Lysozyme from bacteriophage T4 is a 164 amino acid polypeptide chain that folds into two domains (Figure 17.3) There are no disulfide bridges the two cysteine residues in the amino acid sequence, Cys 54 and Cys 97, are far apart in the folded structure. The stability of both the wild-type and mutant proteins is expressed as the melting temperature, Tm, which is the temperature at which 50% of the enzyme is inactivated during reversible beat denat-uration. For the wild-type T4 lysozyme the Tm is 41.9 °C. 

Somatostatin is a tetradecapeptide of the hypothalamus that inhibits the release of pituitary growth hormone. Its amino acid sequence has been determined by a combination of Edman degradations and enzymic hydrolysis experiments. On the basis of the following data, deduce the primary structure of somatostatin ... 

Approximately 500 of the 820 amino acid residues of the myosin head are highly conserved between various species. One conserved region, located approximately at residues 170 to 214, constitutes part of the ATP-binding site. Whereas many ATP-binding proteins and enzymes employ a /3-sheet-a-helix-/3-sheet motif, this region of myosin forms a related a-f3-a structure, beginning with an Arg at (approximately) residue 192. The /3-sheet in this region of all myosins includes the amino acid sequence... 

NOS (eNOS, NOS IH, NOS3). Classically, nNOS and eNOS were considered constitutive enzymes, whereas iNOS is cytokine-induced. Recent evidence suggests that nNOS and eNOS are also subject to important regulation of expression [1 ]. Within the human species, amino acid sequences of the three NOS isoforms share 52-58% identity. Each isoform is well conserved across mammalian species (>90% amino acid identity for nNOS and eNOS, >80% for iNOS). NOS enzymes exist in organisms as low as nematodes, protozoa, and even in plants (Fig. 1). 

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