Single chain enzymes

Icon Interferon-a, / , somatotropin Restriction enzyme Single-chain antibodies Monoclonal antibodies Antigens, Glucocerebrosi-dase, Thaumatin. Albumin DNAse, RNAse inhibitor, Insulin 142-145... 

Streptokinase. Streptokinase is a single-chain protein containing 415 amino acids, mol wt of 45,000 to 50,000 (261,284—286). It is produced by P-hemolytic streptococci and is not an enzyme per se. Only after streptokinase combines with plasminogen on a 1 1 basis to form a... 

Important members of this toxin family are Clostridium difficile toxins A and B, which are implicated in antibiotics-associated diarrhea and pseudomembranous colitis. The large clostridial cytotoxins are single-chain toxins with molecular masses of 250-308 kDa. The enzyme domain is located at the N terminus. The toxins are taken up from an acidic endosomal compartment. They glucosylate RhoA at Thr37 also, Rac and Cdc42 are substrates. Other members of this toxin family such as Clostridium sordellii lethal toxin possess a different substrate specificity and modify Rac but not Rho. In addition, Ras subfamily proteins (e.g., Ras, Ral, and Rap) are modified. As for C3, they are widely used as tools to study Rho functions [2] [4]. 

The a2-plasmin inhibitor, a single-chain glycoprotein (70 kDa), forms rapidly an equimolar complex with plasmin, where the enzyme loses its activity. It is synthesized by the liver and secreted into the blood circulation, where its concentration is 1 pM. 

Figure 10.1. Schematic diagram showing inhibition of synthesis of amino acids a) single chain inhibition occurs when enzyme controlling committed step (S ) is inhibited by increasing concentrations of product AAj b) branched chain inhibition of by increased concentration of AA2 occurs at a post-branching step (sj), while permitting continued production of product of other branch (AAj). In general, each step is controlled by a single enzyme.

This enzyme (RNase A) is a single chain protein of 124 amino acid residues, cross-linked by four intrachain disulfide bonds. Limited proteolysis of the enzyme cuts a single peptide bond between residues 20 and 21 (Richards and Vithayathil, 1959). The derived protein, RNase S, retains enzymic activity although the N-terminal peptide of 20 amino acids (S-peptide) is no longer covalently attached to the balance of the molecule (S-protein). Removal of S-peptide from... 

Whelan and Bailey were also able to clarify the polymerization mechanism of the enzymatic polymerization with phosphorylase [124], Their results showed that the polymerization follows a multichain scheme in contrast to a single-chain scheme that was also proposed by some authors. In the multichain polymerization scheme, the enzyme-substrate complex dissociates after every addition step, whereas in the single-chain scheme each enzyme continuously increases the length of a single primer chain without dissociation. 

An alternative approach to RNA suppression for controlled reduction of flavonoid enzyme activity is the expression of single-chain antibody fragments targeted to a key enzyme or TF. Early attempts with enzymes such as DFR have been inconclusive as to the effectiveness of the technology. 

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