Substrate binding by crude membranes and solubilized membrane extracts fromPseudomonas natriegens

A component formed in the membranes ofPseudomonas natriegens during induction to utilization of mannitol orl-arabinose was found to bind the specific inducing substrate. Chloramphenicol inhibited the synthesis of the component. Binding was optimal at 25–30 C in the presence of Na⁺ and K⁺. Trypsin, KCN, and N-ethylmaleimide destroyed or suppressed the capacity to bind, but DNase and RNase had little effect. Specific binding was demonstrated by equilibrium dialysis with labeled substrate on one side of the dialysis cell and membranes or alkaline extracts of membranes on the other. Membranes from mannitol-grown cells broke the equilibrium established for C¹⁴-labeled mannitol, whereas membranes from cells grown in sea water nutrient broth did not. The substrate was unchanged after binding. Simple alkaline extraction followed by centrifugation at 105,000 ×g for 60 min gave significant purification of the binding component. Specific requirement of Na⁺ and K⁺ for substrate binding by alkaline extracts of membranes could not be demonstrated. The binding capacity of the solubilized component in alkaline extracts was destroyed by heating, but was stable to storage at 0 C for several days.