Table 2.

Yield and cost comparison of the flask expression and fermentation of Exendin‐4 and four variants, namely Tc5b‐D9N, E5, E11 and E19. Ni‐IMAC chromatograms of raw materials were used to estimate the yields and the purity was checked by analytical HPLC (an example for E5 is shown in Supplementary material S2).

Protein name and labelling type	Calculated yield a (mg l−1)		Estimated cost (EUR/10 mg)
	Ferm.	Flask	Ferm.	Flask
E11, 15N	64.8	31.2	18.7	38.8
E19, 15N	150.2	33.5	8.1	36.2
E5, 15N	99.6	19.4	12.2	62.4
Exendin‐4, 15N	87.0	31.4	13.9	38.6
Tc5b D9N, 15N	19.1	12.1	63.5	100.1

^aRaw material yield based on the integral volume of the absorbance curve (see methods), determined after completing the first Ni‐IMAC step.