Plasma membranes of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius (DSM 639) display a pyrophosphate-hydrolyzing activity [M. Lübben & G. Schäfer (1987) Eur. J. Biochem. 164, 533-540]. In our present work, we solubilized and purified this pyrophosphatase to homogeneity. It consists of a single subunit with a molecular mass of 17-18 kDa, forming an oligomer of 70 kDa under native conditions. Edman degradation revealed 30 amino acids of the N-terminus. The enzyme cleaves phosphoric-acid-anhydride bonds independently of monovalent or divalent cations. Temperature and pH optima of 75 degrees C and 3.5-3.7, respectively, characterize it as an ectoenzyme. Membrane lipids of Sulfolobus stimulate the activity. The dolichol-pyrophosphate-complexing peptide-antibiotic bacitracin inhibited growth of Sulfolobus. A possible function of the acid pyrophosphatase is the hydrolysis of dolichol pyrophosphate in connection with glycosylation reactions of membrane proteins.
It has been suggested that small doses of PTH could exert an anabolic effect on bone and could be beneficial in the management of bone diseases secondary to low bone formation. The effects of 20 wk of continuous infusion of 0.05 U.kg-1.h-1 of 1-34 PTH on cellular, structural, and dynamic parameters of bone were studied in inbred beagles. This physiologic or near physiologic dose of PTH caused a small but significant rise in the concentration of serum calcium and a significant increment in the plasma concentration of 1,25(OH)2D. In addition, the sustained infusion of PTH was associated with a significant increment in volume and surface density of osteoid without a change in bone mass. Mineralization of osteoid was not altered, as evidenced by normal double tetracycline uptake and normal osteoid seam thickness. The enhanced osteoid production was not due to augmented bone formation by individual osteoblasts or basic remodeling units but rather to increased activation frequency resulting in an increased number of remodeling units. There was also augmented bone resorption at the tissue level. The data indicate that small doses of PTH do not have an anabolic effect on the skeleton because they are not associated with increased net bone formation. Rather, PTH administration is associated with an increase in coupled bone turnover.
The bioenergetic properties of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius are reviewed and discussed under the aspect whether this archaebacterium conserved energy by oxidative phosphorylation and how the involved catalysts are related to those from eubacteria and eukaryotes. The thermodynamic parameters contributing to the proton‐motive force and the efficiency of proton pumping are presented. The major components of the electron transport system are identified and a novel type of heme‐aa3 containing terminal oxidase is described, oxidizing reduced caldariella quinone. The properties of an F1‐analogous ATPase and of a DCCD‐binding proteolipid from the plasmamembrane of Sulfolobus are discussed as likely components of an F0F1‐analogous ATP‐synthase. The structural and functional properties of this and other archaebacterial ATPases are compared to each other and with respect to evolutionary relations.
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