H+-ATPases in biological systems: an overview of their function, structure, mechanism, and regulatory properties

Renal tubular acidosis and vasculitis associated with IgE deposits in the kidney and small vessels

We report a woman with a history of allergies, polyuria, polydipsia, proteinuria, renal loss of electrolytes, renal tubular acidosis, nephrocalcinosis, and palpable purpura. A proximal defect was excluded by a normal bicarbonate reabsorption curve, and a distal tubular defect was shown because urine pH did not decrease to less than 6.4 despite ammonium chloride-induced systemic acidosis. Moreover, furosemide failed to improve urinary acidification. Urine-to-blood PCO(2) gradient was less than 14 mm Hg, although the urine bicarbonate level reached values as high as 89 mEq/L. Combining bicarbonate and neutral phosphate infusions increased the urine-to-blood PCO(2) gradient to only 20 mm Hg. These subnormal PCO(2) gradient values point to proton-pump dysfunction in the collecting tubule. Histological evidence of tubulointerstitial disease accompanied the tubular defects. The striking histological feature was the presence of immunoglobulin E (IgE) deposits in glomeruli, tubuli, and vessels. Concurrent with these findings, she had high serum IgE titers and CD23 levels. IgE antibodies from her serum were reactive against human renal tubuli, with binding to two regions that matched two different proteins present in cortex and medulla. One of these proteins corresponded to carbonic anhydrase II (31 kd); the second, to an unidentified protein that seems attached to cell membranes. We suggest that these IgE antibodies could have had a pathogenic role in this patient's glomerular, tubular, and small-vessel disease.

Effects of Mg2+ and Ca2+ on Fe2+ uptake by Bifidobacterium thermophilum

Ferrous iron uptake was investigated in Bifidobacterium thermophilum (B. thermophilum) in the presence of Mg2+ and Ca2+ with the following findings: 1. Mg2+ inhibited Fe2+ accumulation in the cells in a dose-dependent manner at 37 degrees, but not at 0 degrees. Removal of Mg2+ from the medium resulted in a resumption of rapid iron uptake. 2. Mg2+ had no effect on the binding of Fe2+ by B. thermophilum protoplasts, its cellular particulate fraction, or distribution between the particulate and soluble fractions. 3. Ca2+ exerted a stimulatory effect on iron uptake by B. thermophilum, but was not able to reverse the inhibitory effects of Mg2+. 4. It was concluded that Mg2+ has no effect on the binding of iron on the surface or interior of B. thermophilum and that it affected the Fe2+ transport mechanism (permease) in a reversible manner. It is possible that iron and magnesium share the same permease in this microorganism.

Cytochemical demonstration of NPPase activity for detecting proton-translocating ATPase of Golgi complex in rat pancreatic acinar cells

An attempt at cytochemical demonstration of acidification proton-translocating ATPase (H(+)-ATPase) of Golgi complex in rat pancreatic acinar cells has been made by using p-nitrophenylphosphatase (NPPase) cytochemistry which is used for detecting of Na(+)-K(+)-ATPase (Mayahara et al. 1980) and gastric H(+)-K(+)-ATPase (Fujimoto et al. 1986). K(+)-independent NPPase activity was observed on the membrane of the trans cisternae of Golgi complex, but not inside of cisternae. The localization of NPPase activity is different from that of acid phosphatase activity where reaction products were seen on the inside of the trans Golgi cisternae. Since this activity was insensitive to vanadate, ouabain and independent of potassium ions, it was distinct from plasma membranous ATPases such as Na(+)-K(+)-ATPase and Ca2(+)-ATPase. The K(+)-independent NPPase activity was diminished by the inhibitors of H(+)-ATPase such as N-ethylmaleimide (NEM) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The NPPase reaction products were also seen on the membranes of other acidic organelles, i.e., lysosomes, endosomes, autophagosomes and coated vesicles. These results suggest that NPPase activity on the membrane of the Golgi complex and other acidic organelles corresponds with H(+)-ATPase which plays a role in acidification.

Structure and function of the ATPase-ATP synthase complex of mitochondria as compared to chloroplasts and bacteria

An overview of the structure and function of the mitochondrial ATPase-ATP synthase complex is presented. Attempts are made to identify the analogies and differences between mitochondrial, chloroplastic and bacterial complexes. The relatively more precise information available on the structure of the E. coli enzyme is used to try and understand the apparently more complex structure of the mitochondrial enzyme. Recent ideas on the mechanism of ATP hydrolysis and ATP synthesis will be summarized.

Chemical crosslinking of alpha subunits in the F1 adenosine triphosphatase of Escherichia coli

The arrangement of the subunits in the F1 adenosine triphosphatase of Escherichia coli has been investigated using bifunctional chemical crosslinking agents to covalently link adjacent subunits in the enzyme molecule. The synthesis of the new cleavable crosslinking agent 2,2'-dithiobis(succinimidyl propionate) is described. The crosslinked products resulting from the reaction of the enzyme with 2,2'- and 3,3'-dithiobis(succinimidyl propionate), 3,3'-dithiobis(sulfosuccinimidyl propionate), disuccinimidyl tartrate, dimethyl adipimidate, 1-ethyl-3[3-(dimethylamino)propyl]carbodiimide, and 1,2:3,4-diepoxybutane were analyzed by "three-dimensional" polyacrylamide gel electrophoresis in which they were resolved first in a two-dimensional system. Following cleavage of the crosslinking bridge in the separated products, the constituent subunits were identified by a further one-dimensional gel electrophoresis step. This procedure greatly improved the precision with which crosslinked subunits could be identified. It largely overcame problems due to abnormal migration of crosslinked species on gel electrophoresis and to the formation of multiple species of the same crosslinked subunit dimers. The following crosslinked subunit dimers were identified: alpha alpha, alpha beta, beta gamma, alpha delta, beta epsilon, and gamma epsilon. The trimer alpha alpha delta was recognized. The formation of alpha alpha over alpha beta dimers was favored when more polar crosslinking agents were used. The constraints placed by the finding of adjacent alpha subunits upon current models for the arrangement of the subunits in the F1 ATPase are discussed.

What family of ATPases does the vacuolar H+-ATPase belong to?

Polyacrylamide gel electrophoresis (PAGE) of partially purified ATPase from vacuoles of Saccharomyces carlsbergensis under non-dissociating conditions revealed 3 bands with ATPase activity. Further PAGE in dissociating conditions showed the similarity in composition of these 3 ATPase preparations. They were assumed to contain the same vacuolar ATPase exhibiting, however, different electrophoretic mobility due to the formation of enzyme complexes with different proteins and phospholipids. The ATPase preparation with the highest electrophoretic mobility contained 6 subunits of 75, 62, 16, 14, 12 and 9 kDa. Inhibitors of vacuolar ATPase [14C]DCCD and [14C]NEM bound to a 9 kDa polypeptide, while [14C]DES associated with a polypeptide of 75 kDa. A partially purified preparation of the vacuolar ATPase was not phosphorylated by [gamma-32P]ATP under conditions when plasma membrane ATPase formed a phosphorylated intermediate. Our results show that vacuolar H+-ATPase consists of several polypeptides, does not form the phosphorylated intermediate, and evidently represents a new type of H+-ATPase of yeast.

The prokaryote-eukaryote interface

Over the past 30 years the study of the sequences of proteins and nucleic acids has produced almost incredible amounts of information, new concepts, and new avenues of research. The beginning was slow: the first peptide hormones sequenced in the early 1950's, the first cytochrome c (horse) in 1961, the first bacterial ferredoxin in 1964, and the first transfer RNA (yeast alanine tRNA) in 1965. In the past 6 years, the rate of data accumulation has accelerated tremendously, primarily due to technological advances in nucleic acid sequencing techniques. For investigators of biological evolution, the sequence data and the new information on genetic mechanisms would prove to be the best evidence for elucidating relationships among the genomes of living organisms and for deducing phylogenetic history. In particular, they needed evidence to decide between the two hypotheses for the origin of eukaryotic cells. Now, less than 20 years since Margulis renewed the investigation of this problem, comparisons of protein and nucleic acid sequences, especially of the small subunit ribosomal RNAs, have answered this question in favor of the endosymbiotic origin of eukaryotic cells. After briefly discussing some of the concepts that helped resolve this controversy and the problems involved in using sequence data for evolutionary studies, we describe a few examples of useful evolutionary trees.

Redistribution of gastric K+-NPPase in vertebrate oxyntic cells in relation to hydrochloric acid secretion: a cytochemical study

Gastric K+-NPPase represents a partial reaction of the (K+-H+)ATPase system, which is considered to be the proton pump in mammalian parietal cells. In the present paper, K+-NPPase activity was cytochemically studied by the method of Mayahara et al. (1980) in gastric glands of birds, amphibia, and mammals, either in the resting state induced by cimetidine or after stimulation of HCl secretion by histamine. The gastric K+-NPPase cytochemical reaction was localized only in oxyntic cells of the gastric mucosa in the three species tested. The subcellular distribution of the K+-NPPase reaction product drastically changes with the secretory state of HCl. In resting cells, the K+-NPPase staining is associated with the membranes of the endocellular tubular system while in HCl-secreting cells, it is associated with the plasma membrane of the elaborate secretory surface characteristic of this functional state. The above results demonstrate that the same enzymatic activity, which is associated with the gastric proton pump, is present in both membranous systems of the oxyntic cell secretory pole. This fact supports the proposal that the tubular system represents a membrane reserve that inserts the proton pump into the luminal plasma membrane in vertebrate oxyntic cells under the action of HCl secretagogues.