A comparison of the urokinase and streptokinase activation properties of the native and lower molecular weight forms of sheep plasminogen.

N.F Paoni,F.J Castellino

doi:10.1016/s0021-9258(17)37766-9

Abstract

Native sheep plasminogen (SPg-a), of molecular weight 86,000 to 90,000, in the presence of sheep plasmin (SPm), is rapidly and specifically degraded to a plasminogen (SPg-b), of molecular weight 80,000 to 82,000, by loss of a peptide from the NH2 terminus of SPg-a. More extensive treatment of SPg-b with SPm results in further loss of a single peptide (P) of molecular weight 29,000 to 32,000 from the NH2 terminus of SPg-b, yielding a much lower molecular weight (50,000 to 52,000) plasminogen (SPg-c) which is fully activatable to SPm. The two affinity chromatography forms of SPg-a (Paoni, N., Violand, B. N., and Castellino, F. J. (1977) J. Biol. Chem. 252, 7725-7732) are activated to SPm by urokinase at approximately the same rate and to the same extent. Although SPg-b is activated to SPm in a manner similar to that of SPg-a, SPg-c free of P appears to be activated significantly more rapidly by urokinase when compared to SPg-b and SPg-a. Addition of P to SPg-c restores the SPg-b and SPg-a activation rates to SPg-c. We show SPg-a, SPg-b, and SPg-c to be insensitive to activation to SPm by streptokinase. However, all sheep plasminogen forms are fully activated by catalytic levels of a 1:1 molar complex of streptokinase and human plasmin. A major reason for the insensitivity of SPg-a, SPg-b, and SPg-c to streptokinase activation results from the rapid degradation of streptokinase to inactive fragments by small amounts of SPm initially formed in the activation.

Highlights

Native sheep plasminogen (SPg-a), of molecular weight 86,000 to 90,000, in the presence of sheep plasmin (SPm), is rapidly and degraded to a plasminogen (SPg-b), of molecular weight 80,000 to
We have previously described the purification and physical characterization of the native and altered, lower molecular weight forms of sheep plasminogen, as well as the large peptide released from sheep plasminogen b (SPg-b) by SPm
The results shown for affinity form 2 SPg-a indicate that the final plasmin formed has a much lower molecular weight than that reported for human and rabbit plasmin

Summary

Introduction

Native sheep plasminogen (SPg-a), of molecular weight 86,000 to 90,000, in the presence of sheep plasmin (SPm), is rapidly and degraded to a plasminogen (SPg-b), of molecular weight 80,000 to. All sheep plasminogen forms are fully activated by catalytic levels of a 1:1 molar complex of streptokinase and human plasmin. Plasminogen is the inactive form of the proteolytic enzyme plasmin and has been found in the plasma of all mammalian species tested to date. This protein can be readily purified from any species by affinity chromatography [1, 2] and detailed analyses of the properties of plasminogen have been forwarded for the rabbit [3,4,5,6,7,8], human (2, 8-U), and sheep [14] systems.

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Conclusion