Isolated reticulate bodies of Chlamydia psittaci were found to transport ATP and ADP by an ATP-ADP exchange mechanism. ATP uptake activity was not detected in elementary bodies. The apparent Km of transport for both ATP and ADP was approximately 5 FM, and the calculated V,n for both was about 1 nmol of nucleotide transported per min per mg of protein. ADP competitively inhibited ATP transport with a Ki of 4.5 FM. Other nucleotides tested had no effect on the uptake of ATP. A magnesium-dependent, oligomycin-sensitive ATPase (ATP phosphohydrolase, EC 3.6.1.3) was associated with reticulate bodies, and most of the transported ATP was hydrolyzed to ADP, which was exchanged for additional, extracellular nucleotide. Some ADP was hydrolyzed to AMP, which exited the cells slowly. Lysine was transported against the electrochemical gradient by reticulate bodies in the presence of ATP. Oligomycin and carbonyl cyanide ptrifluoromethoxyphenylhydrazone inhibited ATP-dependent lysine transport. Lysine exited reticulate bodies when the reticulate bodies were incubated in the presence of ADP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, or a

A major cell envelope protein of Chlamydia psittaci with a molecular weight of approximately 43,000 was identified and partially characterized. It was present at all stages of the C. psittaci developmental cycle. A major protein with a similar molecular weight was also observed in two Chlamydia trachomatis strains.

The attachment of Chlamydia psittaci, strain 6BC, to formaldehyde-fixed and unfixed L cells was studied. Cations were found to be required for attachment to both fixed and unfixed cells. The requirement for cations was largely eliminated when the net negative surface charge on fixed cells was reduced. A high concentration of sodium chloride (0.5 M) prevented binding and removed chlamydiae which were attached to fixed and unfixed cells, whereas non-ionic detergents had no effect on attachment of C. psittaci to fixed cells. The effect of various modifications of C. psittaci and L cell surfaces on attachment was also determined. Of the treatments tested, only trypsinization and periodate oxidation of L cells and acetic anhydride, heat and periodate treatments of C. psittaci reduced binding. Various lectins and high concentrations of neutral sugars had no effect on attachment, whereas, amino sugars and several organic amines inhibited attachment. These results suggest that the initial phase of attachment requires electrostatic interactions between host and parasite surfaces, and that amino and carbohydrate groups on the surface of C. psittaci and glycoproteins on the surface of L cells may be directly or indirectly required for attachment.