Figure 3: Ab fragments smaller in size than a whole Ab can be produced efficiently in E. coli and thus they prove to be better suited to laboratory studies. Stable Fab fragments (50 kDa as against 150 kDa for the whole Ab) have been developed, both chains are kept in the form of heterodimers by the interactions between the variable domains of the heavy and light chains (VH and VL), but above all, by disulphide bridges between the constant domains (CH1 and CL). Smaller fragments called ScFv (25 kDa), consisting of only one VH and one VL linked by a peptide bond (or “linker”), were also developed.