Serine ethanolamine phosphate in avian muscular dystrophy: Mechanism of accumulation in dystrophic muscle and relationship to phospholipid synthesis

Abstract

The cause of the elevated level of serine ethanolamine phosphate (SEP) in dystrophic chicken pectoralis muscle was investigated. It was established that dystrophic muscle has the ability to synthesize SEP, whereas normal pectoralis muscle does not. The SEP synthase activity was localized in the microsomal fraction. Both dystrophic and normal muscle microsomes also contain the opposing enzyme, SEP diesterase, the activity of which is much higher in the dystrophic than in the normal muscle. In intact cells SEP may not be accessible to SEP diesterase. Experiments with 31P NMR revealed that in kidney slices the intracellular SEP concentration was maintained although SEP added to the incubation medium was hydrolyzed. Serine [ 14C]ethanolamine phosphate was not taken up by dystrophic or normal posterior latissimus dorsi and anterior latissimus dorsi muscles. The impermeability of muscle to SEP as well as the virtual absence of SEP in the blood of dystrophic chickens eliminates the possibility that the SEP found in dystrophic muscle is derived from another tissue. The synthesis of SEP in dystrophic posterior latissimus dorsi and in both dystrophic and normal anterior latissimus dorsi was demonstrated using [ 3H]serine as a precursor. The turnover of SEP in these muscles was much slower than the turnover of the serine moiety of serine phospholipids indicating that SEP is not a precursor to phosphatidylserine biosynthesis.