Crotonobetaine reductase fromEscherichia coli — a new inducible enzyme of anaerobic metabolization of L(-)-carnitine

Crotonobetaine reductase fromEscherichia coli 044 K74 is an inducible enzyme detectable only in cells grown anaerobically in the presence of L(-)-carnitine or crotonobetaine as inducers. Enzyme activity was not detected in cells cultivated in the presence of inducer plus glucose, nitrate, γ-butyrobetaine or oxygen, respectively. Fumarate caused an additional stimulation of growth and an increased expression of crotonobetaine reductase. The reaction product, γ-butyrobetaine, was identified by autoradiography. Crotonobetaine reductase is localized in the cytoplasm, and has been characterized with respect to pH (pH 7.8) and temperature optimum (40–45 °C). The K m value for crotonobetaine was determined to be 1.1×10−2M. γ-Butyrobetaine,D(+)-carnitine and choline are inhibitors of crotonobetaine reduction. For γ-butyrobetaine (K i =3×10−5M) a competitive inhibition type was determined. Various properties suggest that crotonobetaine reductase is different from other reductases of anaerobic respiration.