System parameters for convenience kinetics. The homoserine kinase reaction (HK, dotted box) transforms homoserine and ATP into O-phospho-homoserine and ADP (solid arrows). Threonine inhibits the enzyme (dotted arrow). Each node and each arrow carries one of the system parameters: each metabolite is characterised by an energy constant kG, the reaction by a velocity constant kV, and each arrow by a kM or kI value. The system parameters are thermodynamically independent and can assume arbitrary positive values. The turnover rates for forward and backward direction can be computed from the system parameters.