Red cell membrane elasticity as determined by flow channel technique.

The elasticity of red cell membrane was determined in a rectangular flow channel under controlled shear flow. The relation between shear stress and cell extension ratio (lambda) has been analyzed with the use of Evans' two-dimensional model. The deformed cell shapes observed experimentally agreed well with the model with lambda up to 1.4. The best correlation was found at lambda = 1.2. The analysis suggests a nonlinear extensional membrane modulus in the low stress range encountered in the flow channel. In terms of an appropriate strain parameter, the elastic modulus is shown to rise toward the level encountered in micropipette aspiration experiments. The implications of the present findings in modeling of cell mechanics and in cell hemolysis are discussed.     

A spin label study of immobilized enzyme spectral subpopulations

Electron spin resonance (ESR) spin label studies have been carried out to examine the active site conformation of alpha-chymotrypsin before and after immobilization on two types of organic polymer supports: Amberlite XAD-8 and XAD-2. alpha-Chymotryspin was first chemically modified by reaction with methyl-4-phenylbutyrimidate and then inhibited by the active site spin label 4-(2,2,6,6-tetramethyl-piperdine-1-oxyl)-m-flurosulfonylbenzamide. In general, the ESR spectra of the active site lable revealed no significant changes in conformation for most of the enzyme before or after derivatization. On the other hand, two spectral subpopulations (A and B) of spin-labeled enzyme were characterized on the basis of their ESR spectra after immobilization on Amberlite XAD-8. Spectral subpopulation A (distinguished by a highly restrained spectrum) appeared to retain its active site structure and conformation and represented a large majority of the labeled chymotrypsin on the beads. Its presence correlated with the high activity and stability of phenylbutyramidinated chymotryspin on the Amberlite XAD-8 beads. Spectral subpopulation B (distinguished by a very weakly constrained spectrum) appeared to reflect loosely bound or denatured enzyme which was removable upon washing with 40% (v/v) ethylene glycol. Two methods for examining solvent accessibility to the active site lable of the kinetics of ascorbate reduction suggested that both spectral subpopulations had identical accessibilities to the bulk solvent. Paramagnetic broadening of the signal by K(3)Fe(CN)(6) revealed differences in the spin-spin broadening of the A and B components but is deemed and inappropriate indicator of solvent accessibility.     

Separation of fructose and glucose mixture by zeolite Y

Na-, K-, Ba-, and Ca-Y were employed for the separation of fructose and glucose in an adsorption column. Effects of temperature, solvent flow rate, amount of mixture injection, and exchangeable cations on the separation were investigated. Efficiency of separation was used as a criterion to characterize the effectiveness of the separation. The transport and kinetic parameters for the column separation were also presented. From simple pulse experiments and moment analysis, the obtained process information of equilibrium and dynamic parameters might be used to design, operate, and control the separation column. (c) 1992 John Wiley & Sons, Inc.     

Incidence of multinucleated and polyploid aortic smooth muscle cells cultured from different age groups of spontaneously hypertensive rats.

Cell size and incidence of multinucleated, polyploid cells in cultured aortic smooth muscle cells from different age groups of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were compared. Smooth muscle cells from SHR were generally larger than those from WKY, and the percentage of multinucleated smooth muscle cells was always higher in SHR than WKY in the three age groups of rats studied (3-4, 10-12, and 28-30 weeks). In smooth muscle cells from the 3- to 4-week group, there was a positive correlation between cell diameter and the percentage of multinucleated smooth muscle cells. Microdensitometric measurements also showed that the incidence of polyploid smooth muscle cells was always higher in SHR than WKY in the three age groups. There was a positive correlation between DNA density and nuclear area measurements in all the age groups of SHR and WKY. We conclude that cultured aortic smooth muscle cells from different age groups of SHR and WKY contained heterogeneous populations of cells and that, under our culture conditions, the polyploidy of the smooth muscle cells found in vivo was maintained in the SHR and WKY.     

The role of the basement membrane in differential expression of keratin proteins in epithelial cells

Extracellular matrix is considered to play an important role in determining the phenotype of cells with which it interacts. Here we have investigated the possibility that extracellular matrix is involved in specifying the pattern of keratin expression in epithelial cells. For these studies, we have developed an explant system in which epithelial cells from one type of stratified epithelial tissue, namely conjunctiva, are maintained on an extracellular matrix substrate derived from a different tissue, namely cornea. These ocular tissues are ideal for such analyses since they express distinct sets of keratins. For example, bovine conjunctival epithelium processed for immunofluorescence is not recognized by antibody preparations against keratin K3 or K12. In contrast, K3 and K12 antibodies generate intense staining in bovine corneal epithelium. At the immunochemical level, conjunctival cells in situ appear to possess no K12 and only trace amounts of K3, whereas corneal epithelial cells in situ possess both K3 and K12. When conjunctival cells are maintained on a corneal substrate with an intact basement membrane for 10 days in vitro they begin to express keratin K12 as determined by immunofluorescence. On the other hand, conjunctival cells that are maintained on a corneal substrate lacking a basement membrane fail to show staining with K12 antibodies. Conjunctival cells begin to show intense staining using K3 antibodies within about 10 days of being placed in culture regardless of their substrate. These results indicate that basement membrane can play a positive role in determining cell-specific expression of certain keratins such as K12. However, other keratins such as K3 may be "unmasked" and/or their expression may be upregulated simply by placing conjunctival epithelial cells in culture. We speculate that in conjunctiva K3 expression is influenced by certain negative exogenous factors. We discuss the possible means of regulation of keratin expression in our model system.     

Structural and functional relationships of human DNA polymerases

A continuing theme of our laboraory, has been the understanding of human DNA polymerases at the structural level. We have purified DNA polymerases delta, epsilon and alpha from human placenta. Monoclonal antibodies to these polymerases were isolated and used as tools to study their immunochemical relationships. These studies have shown that while DNA polymerases delta, epsilon and alpha are discrete protiens, they must share common structural features by virtue of the ability of several of our monoclonal antibodies to exhibit cross-reactivity. A second approach we have taken is the molecular cloning of human DNA polymerase delta and epsilon. We have cloned the DNA polymerase delta cDNA, and this has allowed us to compare its primary structure to those of human polymerase alpha and other members of this polymerase family. Multiple sequence alignments have revealed that human DNA polymerase delta is also closely related to the herpes virus family of DNA polymerases. In situ hybridization has shown that the human DNA polymerase delta gene is localized to chromosome 19 q13.3–q13.4. In order to further determine the functional regions of the DNA polymerase δ structure we are currently expressing human pol δ inE. coli and baculovirus systems. Other work in our laboratory is directed toward examining the expression of DNA polymerase δ during the cell cycle.     

32P-postlabeling of acrolein-deoxyguanosine adducts in DNA after nuclease P1 digestion.

In order to study the relationship between the level of acrolein-DNA adducts and their biological effects, sensitive methods are needed to quantitate DNA adducts. 32P-postlabeling is one such method that has been widely used and we have adapted the technique to detect acrolein-deoxyguanosine adducts. Adducts formed by the reaction of acrolein and deoxyguanosine-3'-monophosphate were isolated by HPLC. Based on their UV spectra and cochromatography with standards after dephosphorylation with acid phosphatase, these adducts were identified as the nucleotide equivalents of cyclic 1,N2-propanodeoxyguanosine adducts formed by acrolein that have been described by Chung et al. [15]. As nucleotides, the adducts were good substrates for polynucleotide kinase-mediated transfer of phosphate from ATP and were able to be detected by 32P-postlabeling. These adducts were resistant to the activity of nuclease P1 and dinucleoside monophosphates in the form d(G*pN) where G* is the acrolein-guanine adduct also resisted digestion by nuclease P1. Digestion of DNA by nuclease P1 and acid phosphatase resulted in the conversion of normal nucleotides to nucleosides and selective enrichment of the adducts as dinucleoside monophosphates. Using nuclease P1/acid phosphatase digestion, followed by 32P-postlabeling and TLC separation, levels of the two adducts in acrolein-treated DNA were found to be about 6185 and 19,222 nmol/mol.     

Purification, characterization, and molecular cloning of a 60-kDa phosphoprotein in rabbit skeletal sarcoplasmic reticulum which is an isoform of phosphoglucomutase.

A 60-kDa substrate of calmodulin-dependent protein kinase in rabbit "heavy" skeletal sarcoplasmic reticulum (SR) was characterized by purification and cDNA cloning. Purification was achieved by column chromatography using DEAE-Sephacel, heparin-agarose, and hydroxylapatite in 0.5% 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonic acid (CHAPS). Analyses of amino acid sequence and composition indicated that the CHAPS-soluble 60-kDa protein is an isoform of phosphoglucomutase (PGM). cDNAs encoding two isoforms of PGM were isolated from rabbit skeletal muscles. The translated amino acid sequences show that the isoforms, PGM1 and PGM2, differ in the N-terminal 77 amino acids and that PGM2 is identical to the 60-kDa protein in the SR. Northern blot analysis showed that the size of the mRNA encoding PGM2 is 2.4 kilobases. The PGM enzyme activity was markedly inhibited in SR membranes, while perturbation of the membranes with CHAPS or guanidine-HCl recovered the enzyme activity. KCl (0.15-1 M) led to a partial recovery of the enzyme activity suggesting that the charge interaction is not the primary force for PGM-SR interaction. PGM is localized in the heavy fraction of SR, where calsequestrin and Ca2+ release channel are enriched. Our results demonstrate that an isoform of PGM localized in junctional skeletal SR is the 60-kDa substrate of calmodulin-dependent protein kinase.     

Studies of the association and conformational properties of metal-free insulin in alkaline sodium chloride solutions by one- and two-dimensional 1H NMR.

One- and two-dimensional 1H NMR spectroscopy have been employed to probe the association and subsequent conformational changes of metal-free insulin in sodium chloride solution at pH 9 and 9.4. These studies establish that the proton resonances of His(B5) and His(B10) are useful signatures of aggregation and conformation. Changes in chemical shifts and areas of resonances due to the C2 protons of His(B10) and His(B5) and transfer of magnetization experiments served to identify the association as the assembly of tetramer from dimers under our experimental conditions (pH 9.4, [insulin] greater than 1 mM, [NaCl] = 0.1 M). Sodium chloride also alters the equilibrium distribution of species in favor of a tetrameric species. The association equilibrium constant was estimated from area measurements to be approximately 5 x 10(3) M-1 at pH 9.4, 26 +/- 0.1 degrees C, and 0.1 M sodium chloride. Under conditions of 0.1 M sodium chloride concentration, nuclear Overhauser effect experiments in the one- and two-dimensional modes revealed an operative nuclear Overhauser effect between the His(B5) C2 protons and the 2,6 ring protons of a Tyr residue provisionally assigned as Tyr(B16). We conclude that this interaction is a diagnostic signature of a conformational transition whereupon an extended chain from residues B1 to B9 (T-state) is transformed into an alpha-helix (R-state) thus bringing the rings of His(B5) and Tyr(B16) from adjacent subunits across the monomer-monomer interface into van der Waals contact. This conformational flexibility is an added consideration to the discussion of the relevant structure of insulin for receptor binding.