Primary structure, of enzymes

The primary structure of enzymes is determined by peptide covalent bonds joining each amino acid to the neighboring one, as well as by disulfide bonds joining sulfur atoms in two cysteine radicals. 

Photolabeling with enzyme substrates, effectors, or photolabile analogs thereof is one of the most useful means of identifying active site residues within the primary structures of enzymes. We have recently applied this method to the study of the NAD-bind-ing sites of two mono(ADP-ribosyl) transferases, diphtheria toxin (DT) and exotoxin A (PT) from Pseudomonas aeruginosa. Both toxins (after appropriate activation steps) transfer ADP-ribose from NAD to elongation factor 2, and as a side reaction, catalyze the hydrolysis of NAD to ADP-ribose, nicotinamide, and a proton. 

Structural genes (Sj to S4 in the Fig.), which code for the primary structures of enzyme proteins catalys-... 

Fig. 2.16 Primary structure of enzymes. (From http //en.wikiversity.org/wiki/Enzyme structure and function).

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 ... 

Primary structure analysis of phenylphosphate carboxylase of T. aromatica is performed in detail, to clarify the reaction mechanism involving four kinds of subunits. The a, (3, y, 8 subunits have molecular masses of 54, 53, 18, and lOkDa, respectively, which make up the active phenylphosphate carboxylase. The primary structures of a and (3 subunits show homology with 3-octaprenyl-4-hydroxybenzoate decarboxylase, 4-hydroxybenzoate decarboxylase, and vanil-late decarboxylase, whereas y subunit is unique and not characterized. The 18kDa 8 subunit belongs to a hydratase/phosphatase protein family. Taking 4-hydroxybenzoate decarboxylase into consideration, Schiihle and Fuchs postulate that the a(3y core enzyme catalyzes the reversible carboxylation. ... 

Markovic,0 and Jomvall,H (1986) Pectinesterase The primary structure of the tomato enzyme. European Journal of Biochemistry. 158.455-462. 

Ruetschi U, B Odelhdg, S Lindstedt, J Barros-Soderling, B Persson, H Jornvall (1992) Characterization of 4-hydroxyphenylpyruvate dioxygenase. Primary structure of the Pseudomonas enzyme. EurJ Biochem 205 459-466. 

Pseudomonas sp. strain P.J. 874 grown with tyrosine carried out dioxygenation of 4-hydroxyphenylpyruvate to 2,5-dihydroxyphenylacetate accompanied by an NIH shift (Lindstedt et al. 1977). The involvement of a high-spin ferric center coordinated with tyrosine is conclusively revealed in the primary structure of the enzyme (Riietschi et al. 1992). 

In humans, the structural gene locus is on chromosome 19 (M17), and the gene spans over 40 kilobases (kb) including 18 exons and 17 introns (W2, X2). Neu-roleukin, a protein that acts as both a neurotrophic factor and a lymphokine, has been isolated from mouse salivary glands (G7), and subsequently the primary structure of neuroleukin was found to be identical to that of GPI by comparison of the cDNA sequences (C7, FI). The cDNA sequence encodes 558 amino acid residues. The enzyme consists of two identical subunits with a molecular weight of approximately 63,000 and neuroleukin is active as a monomer. 

P5N has two isozymes, P5N-I (pyrimidine nucleotidase) and P5N-II (deoxyri-bonucleotidase) (H6, P2). P5N-I is active principally with pyrimidine substrates at an optimal neutral pH P5N-II activity occurs with both purine and pyrimidine substrates and was maximal with deoxy analogues at an acidic pH optimum. This enzyme was partially purified from human red blood cells and had a molecular weight of 28,000 (T19). The primary structures of both isozymes have not been... 

Fig. 11.2. Schematic representation of the primary structure of secreted AChE B of N. brasiliensis in comparison with that of Torpedo californica, for which the three-dimensional structure has been resolved. The residues in the catalytic triad (Ser-His-Glu) are depicted with an asterisk, and the position of cysteine residues and the predicted intramolecular disulphide bonding pattern common to cholinesterases is indicated. An insertion of 17 amino acids relative to the Torpedo sequence, which would predict a novel loop at the molecular surface, is marked with a black box. The 14 aromatic residues lining the active-site gorge of the Torpedo enzyme are illustrated. Identical residues in the nematode enzyme are indicated in plain text, conservative substitutions are boxed, and non-conservative substitutions are circled. The amino acid sequence of AChE C is 90% identical to AChE B, and differs only in the features illustrated in that Thr-70 is substituted by Ser.

Lamouroux, A., Vigny, A., Faucon Biguet, N. etal. The primary structure of human dopamine-beta-hydroxylase insights into the relationship between the soluble and the membrane-bound forms of the enzyme. EMBO J. 6 3931-3937,1987. 

The amino group of the N-terminal amino acid residue of a peptide will react with the FDNB reagent to form the characteristic yellow DNP derivative, which may be released from the peptide by either acid or enzymic hydrolysis of the peptide bond and subsequently identified. This is of historic interest because Dr F. Sanger first used this reaction in his work on the determination of the primary structure of the polypeptide hormone insulin and the reagent is often referred to as Sanger s reagent. 

As metabolic pathways became clearer, the detailed study of the enzymes involved was facilitated by the introduction of new procedures for isolation, purification, and characterization of proteins. Developments in chromatography in the early 1940s and the introduction of gel electrophoresis allowed more efficient methods to be used to separate proteins and to analyze their primary structure, so that Sanger was able, by 1953, to report the primary structure of insulin (Chapter 10). 

From this first synthesis of an enzyme, two general conclusions were drawn. Firstly, it is possible to begin with free amino adds and to assemble them in the laboratory to give a real protein that possesses true enzymatic activity secondly, a new and independent kind of evidence was provided for the view that the primary structure of a protein determines its tertiary structure. 

Hrdy I, Muller M (1995b) Primary structure of the hydrogenosomal malic enzyme of Trichomonas vaginalis and its relationship to homologous enzymes. J Eukaryot Microbiol 42 593-603... 

The ADSA Committee on Milk Protein Nomenclature (Eigel et al. 1984) presented a tentative nomenclature for the new enzyme membrane proteins. While the primary structures of these proteins have not been established, sufficient information exists to obtain an operational definition. The total protein complement of the membrane as observed is dependent upon the past history of the membrane from its formation to its analysis. Both the temperature and the time of storage before analysis can alter the membrane composition and physical state (Wooding 1971). In addition, plasmin has been shown to be associated with preparations of the membrane, and proteolytic products of the membrane protein have been observed in milk (Hoffman et al. 1979 Kanno and Yamauchi 1979). Therefore, one should use fresh warm raw milk for the study of the native MFGM protein. 

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