Immunocytochemical localization of proteins P1, P2, P3 of glycine decarboxylase and of the selenoprotein PA of glycine reductase,all involved in anaerobic glycine metabolism of Eubacterium acidaminophilum

Antibodies raised against the glycine decarboxylase proteins P1, P2, P3, and the selenoprotein P_A, a component of the glycine reductase complex, were used for immunocytochemical localization experiments. Cells of Eubacterium acidaminophilum from logarithmic growth phase were fixed in the growth media with paraformaldehyde and glutaraldehyde. Fixed cells were embedded by the low-temperature procedure using Lowicryl K4M resin, and the protein A-gold technique was applied for the localization experiments. The vicinity of the cytoplasmic membrane contained about 27% of all gold particles when proteins P1 and P2 were to be localized, 50% for protein P_A, and 61% for protein P3. Double immunocytochemical labeling experiments gave evidence for the existence of a protein P1/P2 complex located predominantly in the cytoplasm, and a P3/P_A complex located at the cytoplasmic membrane. Only in very few instances the labels for proteins P3 and P1 were seen very close together in respective doublelabeling experiments. These results indicate that glycine decarboxylase does not occur in this organism as a complex consisting of all four proteins, but that protein P3, the atypical lipoamide dehydrogenase, takes part in both the glycine decarboxylase as well as in the glycine reductase reaction.