Expression of pro-TGase and TGase in E. coli. (A) SDS-PAGE analysis of TGase expression using single expression vectors. 1, 2: insoluble fractions of E. coli cells harboring pSTG and pTG, respectively; 3, 4: intracellular soluble fractions of cells harboring pSTG and pTG, respectively. 5, 6: supernatant and whole cell extracts of E. coli harboring pSPTG, respectively. (B) SDS-PAGE analysis of TGase expression using co-expression constructs (intracellular soluble fractions). (C) SDS-PAGE analysis of TGase expression using co-expression vectors (insoluble fractions). (D) Intracellular TGase activity of E. coli cells harboring the co-expression constructs. 1-9: E. coli cells harboring pTG-PRO, pTG-SPRO, pSTG-PRO, pSTG-SPRO, pPRO-TG, pPRO-STG, pSPRO-TG, pSPRO-STG, and pSPROT7STG, respectively. The bands of TGase and pro-TGase are indicated by downward and upward arrows, respectively.