Plasmin Subject

Milk contains at least two proteinases, plasmin (alkaline milk proteinase) and cathepsin D (acid milk proteinase) and possibly several others, i.e. two thiol proteinases, thrombin and an aminopeptidase. In terms of activity and technological significance, plasmin is the most important of the indigenous proteinases and has been the subject of most attention. The relevant literature has been reviewed by Grufferty and Fox (1988) and Bastian and Brown (1996). 

Other proteinases. The presence of low levels of other proteolytic enzymes in milk has been reported (see Fox and McSweeney, 1996). Most of these originate from somatic cells, and their level increases during mastitic infection. The presence of cathepsin D, a lysozomal enzyme, in milk suggests that all the lysozomal proteinases are present in milk although they may not be active. These minor proteinases are considered to be much less significant than plasmin, but more work on the subject is necessary. 

P-Casein (13 mg) containing 0.036 fid M-P-C was subjected to plasmin hydrolysis for 45 min and the reaction mixture was dissolved in 7 mL column buffer (5mM Tris—3mM NaCl—urea, pH 8.55) together with 100 mg whole casein that had been alkylated with iodoacetamide. The sample solution was applied to a column (1.6 X 50 cm) of DEAE-cellulose equilibrated with column buffer. Elution was with a NaCl gradient (3.0-155mM) in column buffer (gradient volume, 1.0 L) 5.0 mL fractions were collected. Under the conditions used as as-caseins remained adsorbed to the column K-caseins were eluted in Fractions 35-56 Am measurement (----------) radioactivity (--) (28). 

Rate of Plasmin Hydrolysis. It may be concluded from the above electrophoretic and chromatographic data that partial methylation of a protein does not interfere with the site specificity of plasmin hydrolysis or result in the production of artifactual hydrolytic products. It remained to show what effect methylation had on the rate of hydrolysis by plasmin. M-/3-C was diluted approximately 300-fold with unlabeled protein and subjected to plasmin hydrolysis. The reaction mixture was sampled at various intervals up to 70 min, by which time most of the /3-casein was transformed (see Figure 7, Slots 1-5). The extent of transfer of radioactivity to the reaction products was examined to determine... 

Spectrophotometric analysis of urinary inhibition on the active forms (HMW-UK and LMW-UK) revealed a significant difference between subjects with and without renal calculi (VI). A positive correlation exists between the percentage of inhibition and the urinary urate concentration. Urate inhibits both the LMW-UK and the HMW-UK, but not plasmin. These results are in perfect agreement with reports that stone patients have higher urinary urate concentrations (C2). These observations may explain why allopurinol is administered to kidney stone patients. Allopurinol causes a decrease in urinary urate excretion by inhibiting the xanthine oxidase, which could cause a higher urinary urokinase activity. 

Increase of activity of plasmin of tear was found in patients with traumatic corneal damage (Tervo T. et al., 1988). A significant increasing of tissue plasmin activator, urokinase-type plasminogen activators and plasminogen/plasmin were found for patients with corneal ulcers and thermal or chemical bums relative to the pattern observed in the control subjects (Barlati S. et al., 1990). 

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