Plasmin

The serine endopeptidase plasmin is of special interest in milk technology. 

The plasmin activity is reduced by only 10-17% under the conditions of pasteurization, e. g., 72 °C for 15 s. Storage of pasteurized milk indirectly promotes plasmin activity because the inhibitors of PA are inactivated. Complete thermal inactivation of plasmin is achieved at 120 °C in 15 min and at 142 °C in 18 s. 

Plasmin influences the ripening process, e.g., in Camembert. It is accelerated and aroma formation is improved. In the recovery of caseinates, on the other hand, the separation of plasmin is absolutely necessary. 

---

Rosin is commonly modified with maleic or fumaric acid to improve efficiency. Since the 1970s, dispersions of unsaponifted rosin have become more popular as a result of their improved sizing efficiency, lower alum requirements, and reduced pH sensitivity vs saponified rosins. Cationic dispersed rosin size, which can be effective at near-neutral and neutral papermaking conditions, is also available (63—65). Commercially available rosin sizes include Pexol, Neuphor, and Hi-pHase (Hercules Inc.), Plasmine and NeuRos (Plasmine), Stafor (Westvaco), Novaplus, and Novasize (Georgia Pacific), and NeuRos and Roscol (Akzo Nobel). 

Thrombin, the two-chain derivative of the prothrombin molecule, has a molecular weight of approximately 37,000 daltons. Its proteolytic properties induce the conversion of fibrinogen to fibrin to produce the initial visible manifestation of coagulation, the soluble fibrin clot. In addition, thrombin influences the activity of Factors V, VIII, and XIII and plasmin. Thrombin affects platelet function by inducing viscous metamorphosis and the release reaction with subsequent aggregation. 

Coagulation Factors II, III, VII, IX, X, XI, and Xlla fragments, thrombin, and plasmin are classified as serine proteases because each possesses a serine residue with neighboring histidine and asparagine residues at its enzymatically active site (Table 3). Factors II, VII, IX, and X, Protein C, Protein S, and Protein Z are dependent on the presence of vitamin K [84-80-0] for their formation as biologically functionally active procoagulant glycoproteins. 

Although the precise mechanism of plasminogen activation is unknown, three principal theories have developed based on studies of the in vitro activation of native human plasminogen. Activation of native Glu-plasminogen in the absence of any plasmin inhibitor yields Lys —plasmin plus the so-called pre-activation peptides (PAP) formed by cleavage at LySg2 S E3 Activation takes place by a two-step mechanism in... 

The high affinity LBS is involved in the interaction of plasminogen with fibrin, a2-antiplasmin, and a plasmin inhibitor called histidine-rich glycoprotein. It has been observed that plasminogen activation takes place on the surface of fibrin and that a2-antiplasmin competitively inhibits the plasminogen—fibrin interaction at the high affinity LBS. 

The kinetic data for the action of plasmin on different substrates under various conditions have been summarized. The MichaeHs-Menten constant (iC ) varies between 10 and 1000 mAf and the catalytic constant between 1 and 75. ... 

The actions of plasmin on both fibrin and fibrinogen have been studied extensively. Plasmin cleaves fibrin and fibrinogen into a family of fragments known as fibrinogen and fibrin (FDP-fdp) degradation products. 

The degradation of fibrin by plasmin is more complex because the fibrin molecule is a cross-linked polymer. Fragments released include D—D dimer or D2 (two cross-linked D fragments) with a molecular weight of 160,000 daltons, D2E, which is beHeved to be the principally released fragment in vivo, and... 

---