The sensitivity of flux (through the pathway) to other parameters in kinetic expressions for each enzyme can also be estimated under different growth conditions (temperature, pH, etc). This will provide guidance for useful metabolic engineering leading to acceleration of the pathway. Since generally several steps are rate-limiting in a pathway, sequential improvement of metabolic pathway through repeated cycles of metabolic engineering may be required in some cases. Unanticipated cell responses to metabolic engineering are also noticed, which need to be corrected before its practical application. This would require mathematical simulation of responses, modeling and other theoretical exercises using computers. These are the subjects of chemical engineering and are beyond the scope of this book.