The metabolism of the Myxomycete plasmodium (Physarum polycephalum) was investigated by using Warburg manometers. The following results were obtained.
1. Qo2 value on a wet weight basis was 1.08 (M/45 phosphate buffer at pH 6.0), which was 7.3 on a dry weight basis and 140 on a total nitrogen basis.
2. R. Q. value was found to be 0.83 in average.
3. Respiration was affected not only by the pH, but also by the concentration of the buffer. From pH 4.0 to pH 7.0, the respiratory rate was almost constant.
4. O2 uptake was strongly inhibited by various metabolic poisons such as cyanide, NaN3 and monoiodoacetate. CO inhibited respiration considerably, but the inhibition was reversed to some extent upon illumination. Effects of the other inhibitors (2, 4-dinitrophenol, NaF, malonate, phenylthiourea and thiourea) were also investigated. Considering the effects of these inhibitors, the terminal oxidase in the respiration of the plasmodium is suggested to be the cytochrome oxidase. Further support of this was afforded by the spectroscopic confirmation of cytochromes a, b and c.
5. No marked increase of O2 consumption was brought about by the addition of various substrates.
6. Under anaerobic condition, the plasmodium showed the fermentation which was accompanied by acid formation. No sign of aerobic fermentation was observed.
These results show that the metabolism of the plasmodium is very similar to that of muscular tissues.
