Aerobic electron transport in Propionibacterium shermanii. Effects of cyanide

Utilization of Lactate Isomers by Propionibacterium freudenreichii subsp. shermanii: Regulatory Role for Intracellular Pyruvate

Five strains of Propionibacterium freudenreichii subsp. shermanii utilized the l-(+) isomer of lactate at a faster rate than they did the d-(-) isomer when grown with a mixture of lactate isomers under a variety of conditions. ATCC 9614, grown anaerobically in defined medium containing 160 mM dl-lactate, utilized only 4 and 15% of the d-(-)-lactate by the time 50 and 90%, respectively, of the l-(+)-lactate was used. The intracellular pyruvate concentration was high (>100 mM) in the initial stages of lactate utilization, when either dl-lactate or the l-(+) isomer was the starting substrate. The concentration of this intermediate dropped during dl-lactate fermentation such that when only d-(-)-lactate remained, the concentration was <20 mM. When only the d-(-) isomer was initially present, a similar relatively low concentration of intracellular pyruvate was present, even at the start of lactate utilization. The NAD-independent lactate dehydrogenase activities in extracts showed different kinetic properties with regard to pyruvate inhibition, depending upon the lactate isomer present. Pyruvate gave a competitive inhibitor pattern with l-(+)-lactate and a mixed-type inhibitor pattern with d-(-)-lactate. It is suggested that these properties of the lactate dehydrogenases and the intracellular pyruvate concentrations explain the preferential use of the l-(+) isomer.

Multiple forms of cytochrome b in the electron transport system of Propionibacterium shermanii

Membrane particles from Propionibacterium shermanii contain cytochromes b and d as the major cytochrome components. Potentiometric titration of the membranes indicate two distinct groups of b-type cytochromes differing in their midpoint potentials by at least 100 mV. Low temperature spectra of redox-poised membranes show that the high potential group consists of two components with approximate lambda max and midpoint potentials as follows: cytochrome b562-563 (+120 mV); cytochrome bHP556-557 (+90 mV). Resolution of the low potential group of b-type cytochromes is less clear cut but there appear to be two further components with different lambda max values but very similar midpoint potentials: cytochrome bLP556-557 (-20 mV) and cytochrome b553-554 (-20 mV). Cytochrome d630 titrates as a single species with an approximate midpoint potential of +140 mV. The low potential pair of b-type cytochromes have midpoint potentials sufficiently low to permit their functioning as components of the anaerobic electron transport path to fumarate while the high potential pair of b-type cytochromes and cytochrome d probably function on an aerobic branch of the electron transport pathway. The characteristics of the aerobic and anaerobic steady-state spectra are largely consistent with these suggestions.