Assessment of nodal rigidity and its response to metabolic engineering
Information on the degree of nodal rigidity can be obtained using mathematical models of metabolism, metabolic control theory (MCT) or biochemical system theory (BST). The types of alternations used for these models to assess rigidity are, however, case specific and can be classified into following four general categories : (i) attenuation of enzyme activity using an inhibitor; (ii) amplification of attenuation of enzyme activity through genetic modification; (iii) environment perturbation, such as change in carbon source; (iv) deregulation of a different metabolite to increase metabolic burden. Using these techniques, rigidity of G6P, Pyr and PEP principal nodes in lysine biosynthesis network could be assessed.

Nodal rigidity in dependent networks presents even greater problems for metabolic engineering. In, if node 1 or node 2 is rigid, then attenuation of B1 synthesis would not affect the yield of P, but its synthesis rate will be correspondingly attenuated thus causing metabolic collapse. Response in dependent network is independent of the location of rigidity, since alterations are needed at all nodes for coordinated flux partitioning at these nodes.