Activity, isoenzyme pattern, and synthesis of UDPglucose 4-epimerase during differtiation of Physarium polycephalum

1. The specific activity of UDPglucose 4-epimerase (EC 5.1.3.2) increases by about 50% during the first 24 h of starvation-induced differentiation (spherulation) of Physarum polycephalum. 2. At all stages during differentiation, the enzyme activity is very sensitive to actinomycin-C and cycloheximide, inhibitors of transcription and translation, with a half life against cycloheximide of about 20 min (if added 12 h after the induction of differentiation). 3. The isoenzyme pattern, as revealed by isoelectric focusing in sucrose gradients, does not change during spherulation. One main band with a pI of 6.7, with a shoulder (pI 7.6) and a minor band (pI 6.0) was observed in extracts both from growing and differentiating cultures. 4. Density labelling experiments using deuterated amino acids with subsequent analysis by equilibrium density gradient sedimentation in 15-35% (w/w) metrizamide gradients revealed a rather slow rate of enzyme synthesis, which is in contrast to the observed high sensitivity against actinomycin-C and cycloheximide.