The inducible cholinesterase produced by the Goldstein strain of 3Pseudonzonas $uorescelzs was purified t o a state of electrophoretic homogeneity. The enzyme, which resembles a n acetylcholinesterase in its s~abstrate specificity, has a high affinity for acetylcholiale a i d propionylcholine. The estinaated values of K, a t pH 7.4 and 37 "C are 1.4 X 10-6 11.1 for acetylchoIiile and 2.0 X llf for propicanylchdine. The bacterial cholinesterase reacts very slowly with tetraethyl pyrophosghate (TEPP) and diisopropyl phosphorofluoridate (DFP) but coinparatively rapidly with ethyl N,N-dimethylphosphoran1idocyanidate (Tabual). Birnolecnlar rate constants range from 7.7 mol-I min-l for TEFP to 7.4 X lo4 mol-1 min-1 for Tabun. The reactions of the chdinesterase depend upon the ionic state of groups ill the enzyme whose pK, values are in the same range as those reported for other esterases. The results suggest that the enzyme inay be similar in structure t o other cholinesterases, and that both histidine and serine may be involved in its activities.

The sequential development of intracellular antigens in cultured human embryonic fibroblasts infected with the AD-169 strain of cytomegalovirus was studied by means of antiglobulin, direct, and anticomplement immunofluorescent staining.Direct immunofluorescent staining, although less sensitive than the antiglobulin or anticomplement methods for the detection of early diffuse nuclear antigens, gave the clearest definition of the typical intracellular inclusions produced by cytomegalovirus.Quantitative complement fixation assays, carried out in parallel with anticomplement staining, showed that complement is fixed strongly by the intracellular antigens which develop in the late stages of infection.

The inducible cholinesterase of Pseudomonas fluorescens (Goldstein strain) was purified by fractionation on a CM-Sephadex column. The method was found to be superior to alumina C γ gel fractionation in terms of yield, specific activity of the enzyme, and reproducibility of results.