Association of spectrin with desmin intermediate filaments

The association of erythrocyte spectrin with desmin filaments was investigated using two in vitro assays. The ability of spectrin to promote the interaction of desmin filaments with membranes was investigated by electron microscopy of desmin filament-erythrocyte inside-out vesicle preparations. Desmin filaments bound to erythrocyte inside-out vesicles in a spectrin-dependent manner, demonstrating that spectrin is capable of mediating the association of desmin filaments with plasma membranes. A quantitative sedimentation assay was used to demonstrate the direct association of spectrin with desmin filaments in vitro. When increasing concentrations of spectrin were incubated with desmin filaments, spectrin cosedimented with desmin filaments in a concentration-dependent manner. At near saturation the spectrin:desmin molar ratio in the sedimented complex was 1:230. Our results suggest that, in addition to its well characterized associations with actin, spectrin functions to mediate the association of intermediate filaments with plasma membranes. It might be that nonerythrocyte spectrins share erythrocyte spectrin's ability to bind to intermediate filaments and function in nonerythroid cells to promote the interaction of intermediate filaments with actin filaments and/or the plasma membrane.     

Isolation and Partial Characterization of the Major Amide-Linked Conjugate of Indole-3-Acetic Acid from Phaseolus vulgaris L

A major indole-3-acetic acid conjugate from Phaseolus vulgaris seed has been isolated and partially characterized. It is a 3 kilodalton peptide with apparently 2 indole-3-acetyl moieties in amide linkage per peptide. The indole-3-acetic acid component was identified by gas chromatography-mass spectrometry and the peptide characterized by polyacrylamide gel electrophoresis, by amino acid analysis using dabsyl derivatives and by its Fourier transform-infrared spectrum. This is the first higher molecular weight amide-linked indole-3-acetic acid conjugate to be characterized from higher plants.     

Hybridization of cloned Rhodopseudomonas capsulata photosynthesis genes with DNA from other photosynthetic bacteria

The homology of Rhodopseudomonas capsulata DNA segments carrying photosynthesis genes with sequences present in total DNA from certain other photosynthetic and non-photosynthetic bacterial species was determined by hybridization. R. capsulata DNA fragments that carry loci for production of peptide components of the photosynthetic reaction center and light-harvesting I antenna complex were found to hybridize to DNA from some photosynthetic species. However, fragments that carry carotenoid or bacteriochlorophyll biosynthesis genes showed either weak or undetectable heterospecific hybridization under the conditions employed.     

Immunochemical characterization of related families of glycoproteins in desmosomes

Using several biochemical approaches, we have characterized the relatedness of the various glycoprotein components of the bovine epidermal desomosome. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of purified epidermal desmosomes reveals 12 proteins, of which 8 are glycosylated. Analysis with monoclonal antibodies indicates that the 8 glycoproteins comprise 3 antigenically distinct protein families. Members of the highest molecular weight glycoprotein family (a triplet of Mr = 150,000) were not distinguishable by partial proteolytic peptide mapping. At least 6 different monoclonal antibodies have been identified that recognize unique antigenic determinants shared by these proteins. Members of a 97,000-118,000-dalton glycoprotein family (about 4 bands) generate very similar but not identical partial proteolytic peptide maps. At least 3 different monoclonal antibodies have been identified that recognize unique antigenic determinants shared by these proteins. A Mr = 22,000 glycoprotein is immunologically unrelated to either of the high molecular weight glycoprotein families. Lectin-binding profiles indicate that within each immunologically related family the glycoproteins are similar in their oligosaccharide composition. Some lectins distinguish among the families. These glycoproteins probably mediate the specific intercellular recognition and adhesive functions of the desmosome.     

A kinetic analysis of the effects of inhibitor-1 and inhibitor-2 on the activity of protein phosphatase-1

The steady-state interaction between protein phosphatase-1 and its two inhibitor proteins was studied in vitro at low enzyme concentrations where the assumptions of the Michaelis-Menten equation appeared to be valid. Under these conditions, and in the absence of divalent cations, inhibitor-1 behaved as a mixed inhibitor using phosphorylase alpha as a substrate, whereas inhibitor-2 was a competitive inhibitor. The results demonstrate that inhibitor-1 and inhibitor-2 do not interact with protein phosphatase-1 in an identical manner. Inhibitor-1 was only a substrate for protein phosphatase-1 in the presence of Mn2+, and its dephosphorylation was inhibited competitively by inhibitor-2 (Kis = 8 nM). Inhibitor-1 did not inhibit its own dephosphorylation in the presence of Mn2+. Its Km as a substrate (190 nM) was very much higher than its Ki as an inhibitor (1.5-7.5 nM). The results are consistent with a model in which a single binding site for inhibitor-1 is present on protein phosphatase-1, distinct from the binding site for phosphorylase alpha. It is envisaged that the binding of inhibitor-1 to this site not only inhibits the dephosphorylation of other substrates but permits access of its phosphothreonine to the same catalytic group(s) responsible for the dephosphorylation of other substrates. G-substrate, a protein phosphorylated exclusively on threonine residues, did not inhibit the dephosphorylation of phosphorylase alpha and its dephosphorylation was potently inhibited by inhibitor-1 or inhibitor-2. The role of the phosphothreonine residue in inhibitor-1 is discussed in the light of these results.     

Centriole as microtubule-organizing centers for marginal bands of molluscan erythrocytes

The erythrocytes of blood clams (arcidae) are flattened, elliptical, and nucleated. They contain elliptical marginal bands (MBs) of microtubules, each physically associated with a pair of centrioles marginal bands (MBs) of microtubles, each physically associated with a pair of centrioles (Cohen, W., and I. Nemhauser, 1980, J. Cell Biol., 86:286-291). The MBs were found to be cold labile in living cells, disappearing within 1-2 h at 0 degrees C. After the cells had been rewarmed for 1-2 h, continuous MBs with associated centrioles were once again present. Time-course studies utilizing phase contrast, antitubulin immunofluorescence, and electron microscopy of cytoskeletons prepared during rewarming revealed structural evidence of centriole participation in MB reassembly. At the earliest stage of reassembly, a continuous MB was not present. Instead, relatively short and straight microtubules focused on a pointed centriolar “pole,” and none were present elsewhere in the cytoskeleton. Thin continuous MBs then formed, still pointed in the centriolar region. Subsequently, the MBs regained ellipticity, with their thickness gradually increasing but not reaching that of controls even after several hours of rewarming. At these later time points, microtubules still radiated from the centrioles and joined the MBs some distance away. In the presence of 0.1 mM colchicines, MB reassembly was arrested at the pointed stage. Electron microscopic observations indicate that pericentriolar material is involved in microtubule nucleation in this system, rather than the centriolar triplets directly. The results suggest a model in which the centrioles and associated material nucleate assembly and growth of microtubules in diverging directions around the cell periphery. Microtubules of opposite polarity would then pass each other at the end of the cell distal to the centrioles, with continued elongation eventually closing the MB ellipse behind the centriole pair.     

Glycopeptides of the Type-Common Glycoprotein gD of Herpes Simplex Virus Types 1 and 2

We have carried out detailed structural studies of the glycopeptides of glycoprotein gD of herpes simplex virus types 1 and 2. We first examined and compared the number of N-asparagine-linked oligosaccharides present in each glycoprotein. We found that treatment of either pgD-1 or pgD-2 with endo-β-N-acetylglucosaminidase H (Endo H) generated three polypeptides which migrated more rapidly than pgD on gradient sodium dodecyl sulfate-polyacrylamide gels. Two of the faster-migrating polypeptides were labeled with [³H]mannose, suggesting that both pgD-1 and pgD-2 contained three N-asparagine-linked oligosaccharides. Second, we characterized the [³H]mannose-labeled tryptic peptides of pgD-1 and pgD-2. We found that both glycoproteins contained three tryptic glycopeptides, termed glycopeptides 1, 2, and 3. Gel filtration studies indicated that the molecular weights of these three peptides were approximately 10,000, 3,900, and 1,800, respectively, for both pgD-1 and pgD-2. Three methods were employed to determine the size of the attached oligosaccharides. First, the [³H]mannose-labeled glycopeptides were treated with Endo H, and the released oligosaccharide was chromatographed on Bio-Gel P6. The size of this molecule was estimated to be approximately 1,200 daltons. Second, Endo H treatment of [³⁵S]methionine-labeled glycopeptide 2 reduced the molecular size of this peptide from approximately 3,900 to approximately 2,400 daltons. Third, glycopeptide 2 isolated from the gD-like molecule formed in the presence of tunicamycin was approximately 2,200 daltons. From these experiments, the size of each N-asparagine-linked oligosaccharide was estimated to be approximately 1,400 to 1,600 daltons. Our experiments indicated that glycopeptides 2 and 3 each contained one N-asparagine-linked oligosaccharide chain. Although glycopeptide 1 was large enough to accommodate more than one oligosaccharide chain, the experiments with Endo H treatment of the glycoprotein indicated that there were only three N-asparagine-linked oligosaccharides present in pgD-1 and pgD-2. Further studies of the tryptic glycopeptides by reverse-phase high-performance liquid chromatography indicated that all of the glycopeptides were hydrophobic in nature. In the case of glycopeptide 2, we observed that when the carbohydrate was not present, the hydrophobicity of the peptide increased. The properties of the tryptic glycopeptides of pgD-1 were compared with the properties predicted from the deduced amino acid sequence of gD-1. The size and amino acid composition compared favorably for glycopeptides 1 and 2. Glycopeptide 3 appeared to be somewhat smaller than would be predicted from the deduced sequence of gD-1. It appears that all three potential glycosylation sites predicted by the amino acid sequence are utilized in gD-1 and that a similar number of glycosylation sites are present in gD-2.     

Epinephrine: A Potential Neurotransmitter in Retina

Abstract: Dopamine (DA), norepinephrine (NE), and epinephrine (EPI) are present in rat retina. DA is the major catecholamine, whereas NE and EPI represent ∼5% of the DA content. DA is contained in a subpopulation of amacrine cells and has been the subject of numerous studies. We investigated the origin and properties of NE and EPI in retina. Following superior cervical ganglionectomy, there was a decrease in NE content, but no decrease in EPI or phenylethanolamine- N -methyltransferase (PNMT) activity. PNMT in retina has many of the substrate-specificity and inhibitor-sensitivity characteristics of other tissues. Enzyme activity is enhanced in newborn rats by treatment with dexamethasone. Exposure to a lighted environment increases retinal EPI in normal and superior cervical ganglionectomized rats. EPI content increased for more than 2 h in a lighted environment. We conclude that most of the NE is contained within the sympathetic neurons that innervate the eye from the superior cervical ganglion, whereas EPI is contained in retinal elements that are responsive to photic stimulation.