The Complete List of Suppliers for L-Serine,1,1'-[[5-[(1S)-4-[(aminoiminomethyl)- amino]-1-carboxybutyl]hexahydro-4,6-dioxo- 1H-furo[3,4-c]pyrrole-1,3-diyl]dicarbonyl]bis- [L-arginylglycyl-L-R-aspartyl-,(1f1'')- amide with glycyl-L-R-aspartyl-L-serine