How is plasmin formed from plasminogen?
Tissue plasminogen activator is a serine protease consisting of approximately  530 amino acids and about 13% carbohydrate. 

This enzyme is made up of five domains performing different functions. The finger domain and the two kringle domains are involved in the binding of t-PA to fibrin, whereas the epidermal growth factor domain is responsible for activating EGF receptor. Kringle 1 also help in transport of this molecule via liver's endothelial cells. Kringle 2 also helps in binding with inactive plasminogen. The serine protease domain cleaves the plasminogen at  Arg561-Val562  and activates it into plasmin.



(Image Source: https://www.researchgate.net/figure/Structure-and-functions-of-tissue-type-Plasminogen-Activator-tPA-A-Structure-of_fig1_284797342)

Plasminogen is the precursor for synthesis of protease plasmin. Plasminogen is converted to plasmin by cleaving Arg561 and Val562. The  activated plasmin is formed by making disulfide-linkage between these two polypeptide chains. 

The heavy chain  is at the N-terminal and light chain is at C-terminal.  The activation takes place by removing the signal peptide and activation peptide  by autolytic cleavage. This activation peptide is released from the N-terminal  to convert Glu-plasmin to  Lys-Plasmin. The active site which plays role in binding with fibrin is situated on the light chain.



(Image Source:  https://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/plasmin.html)

So, this proteolysis only produces one working peptide sequence, as the peptide bond cleaved and then amino acids are again joined by disulfide bond. And this peptide bond between arginine and valine is at 561/562 instead of 560/561 according to various sources.