A Constitutive Enzyme System for Glucose Transport by Chlorella sorokiniana

Abstract

It was found that the transport system for glucose (as measured by deoxyglucose uptake) in the high temperature strain of Chlorella (strain 07-11-05 or C. sorokiniana) was constitutive and the rate of uptake did not increase upon incubation of autotrophicaily grown cells with either deox-yglucose or glucose. The uptake obeyed Michaelis-Menten type kinetics with a concentration of 200 micromolar for half-saturation. The maximum rate of uptake was nearly 10 times faster per cell (at 38 C) than that reported for any other Chlorella. This rapid accumulation of deoxyglucose causes the passive efflux to become significant compared to the pump-driven influx and nonlinear uptake appears even after only 3 to 4 minutes. Tanner, Komor, and others (3, 4, 6, 12) have demonstrated that the glucose transport system in several species of Chlorella requires at least a 1-h incubation in glucose for induction (12). The system utilizes a permease which manifests Michaelis-Menten kinetics (4), requires an energy source (6), and cotransports a proton during the transport of glucose (3). We found a constitutive glucose transport system in the high temperature strain of Chlorella (07-11-05 or C. sorokiniana). A