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An enzymic activity of rat brain that liberates radioactive free aldehydes from 1-[1-14C]alk-1'-enyl-sn-glycero-3-phosphoethanolamine (lyso-plasmalogen) is described. It was present mainly in microsomal fractions (crude) of brains of rats of different ages. The highest specific enzyme activity was found in 21-day-old animals. The formation of free aldehyde was dependent on the amount of enzyme protein as well as the amount of substrate added, and was linear to the incubation time up to 60 min. The pH optimum was between 7.1 and 7.3. Bivalent cations (Mg2+, Ca2+) and detergents inhibited the reaction. However, the same cell fractions as well as extracts of acetone-dried powder of brain from young or old rats possessed no enzyme activity for liberating the aldehyde from the acylated substrates: 1-[1-14C]alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine (plasmalogen) or plasmalogen of ox corpus callosum.

99m Tc-ubiquicidin (UBI) 29-41 is under clinical evaluation for discrimination between bacterial infection and unspecific inflammation. We compared the distribution of 99m Tc-UBI 29-41, the potential PET tracers 18 F-UBI 29-41 and 18 F-UBI 28-41, and 3 H-deoxyglucose (DG) in rat muscle abscesses to that of antiStaphylococcus aureus immunofluorescent imaging. Methods: Calf abscesses were induced in 15 CDF-Fischer rats after inoculation of Staphylococcus aureus. One to 6 d later, either 18 F-UBI 29-41 and 3 H-DG (n 5 5) or 18 F-UBI 28-41 and 3 H-DG (n 5 6) or 99m Tc-UBI 29-41 and 3 H-DG (n 5 4) were injected simultaneously. Dual-tracer autoradiography of the abscess area was compared with the distribution of bacteria and macrophages. Results: The UBI derivates exhibited increased uptake in the abscess area that partly matched 3 H-DG uptake and macrophage infiltration but showed no congruity with areas that were highly positive for bacteria. Conclusion: A specific binding of UBI derivatives to Staphylococcus aureus in vivo could not be confirmed in this study.

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