Ligand-sensitive interactions among the transmembrane helices of Na+/K+-ATPase

An extensively trypsin-digested Na+/K+-ATPase, which retains the ability to bind Na+, K+, and ouabain, consists of four fragments of the alpha-subunit that contain all 10 transmembrane alpha domains, and the beta-subunit, a fraction of which is cleaved at Arg142-Gly143. In previous studies, we solubilized this preparation with a detergent and mapped the relative positions of several transmembrane helices of the subunits by chemical cross-linking. To determine if these detected helix-helix proximities were representative of those existing in the bilayer prior to solubilization, we have now done similar studies on the membrane-bound preparation of the same digested enzyme. After oxidative sulfhydryl cross-linking catalyzed by Cu2+-phenanthroline, two prominent products were identified by their mobilities and the analyses of their N termini. One was a dimer of a 11-kDa alpha-fragment containing the H1-H2 helices and a 22-kDa alpha-fragment containing the H7-H10 helices. This dimer seemed to be the same as that obtained in the solubilized preparation. The other product was a trimer of the above two alpha-fragments and that fraction of beta whose extracellular domain was cleaved at Arg142-Gly143. This product was different from a similar one of the solubilized preparation in that the latter contained the predominant fraction of beta without the extracellular cleavage. The cross-linking reactions of the membrane preparation, but not those of the solubilized one, were hindered specifically by Na+, K+, and ouabain. These findings indicate that (a) the H1-H2 transmembrane helices of alpha are adjacent to some of its H7-H10 helices both in solubilized and membrane-bound states, (b) the alignment of the residues of the single transmembrane helix of beta with the interacting H1-H2 and H7-H10 helices of alpha is altered by detergent solubilization and by structural changes in the extracellular domain of beta, and (c) the three-dimensional packing of the interacting transmembrane helices of alpha and beta are regulated by the specific ligands of the enzyme.     

The zeta protein kinase C isoform from the testis of the grey mullet Mugil cephalus with a specific reaction protein of M(r) 48,000 on oolemma

The zeta protein kinase C isoform (PKC-zeta) was purified from the testis of the grey mullet Mugil cephalus and has relative masses (M(r)) of 65,000 and 63,000. The subunits of PKC-zeta from spermatozoa degenerated to M(r) 58,000 and 53,000 after continuous freezing and thawing. Proteins of M(r) 48,000 on the oolemma of the grey mullet Mugil cephalus were found to be the reaction proteins of the PKC-zeta from spermatozoa.     

The x-ray morphometric characteristics of the spine in persons 50 and older

To specify shape of the vertebra in relation to age and sex, the authors studied roentgenomorphometric evidence upon examination of the thoracic and lumbar spine in 600 patients over 50. Vertebral deformities were found in 45.1 and 44.5% of the examined males and females, respectively. Changes corresponding to vertebral body fracture were recorded in 12.3% of the males and 15.3% of the females. Age-related trends in the frequency of various defects have been analyzed. The frequency differed in males and females.