Export of Polymalate and Polymalatase from Microplasmodia of Physarum polycephalum

Anton Brandlmaier and Eggehard Holler

Institut fuer Biophysik und Physikalische Biochemie, Universitaet Regensburg, D-93040 Regensburg, Germany

Polymalate and polymalatase have been previously prepared from the culture medium of the plasmodial cell form of Physarum polycephalum. Ongoing work is now directed towards the mechanism(s) of the secretion. In first experiments, we examined whether phosphate-buffered-saline (PBS) is an appropriate medium to investigate the export. By measuring the release of yellow pigment and the uptake of Trypan Blue, we found that plasmodia are leaky and subsequently lysed in this buffer, and that the observed efflux of polymalate paralleled the release of the pigment from the leaky cells (Fig. 1). Acceptable conditions were fresh medium/PBS (1:1, vol/vol) exhibiting no pigment release over 2 h at room temperature. Under green light, polymalate accumulated in a linear fashion during 60 min after medium change (Fig. 2). A strong dependence on the incubation temperature (Fig. 3, above 32 C the plasmodia became leaky) and inhibition by Brefeldin-A (data not shown) indicated that polymalate was transported via the Golgi-dependent export pathway. Work is directed towards elucidation of the export mechanism, especially whether polymalatase is involved as a transporter.