Biomedical subjects

D L Helseth

Publications and source records attributed to D L Helseth.

5 recordsLinked to original sources

PubMed1989

Incomplete polymerization of Cavalite with the use of recommended photopolymerization times: a warning of possible cytotoxic effects.

As part of a study of the suitability of new materials for use as a retrofilling material, we examined the polymerization properties of Cavalite, a light-cured, hydroxyapatite and glass ionomer-containing cavity liner. By varying the time of photopolymerization, it was found that polymerization for 20 to 30 seconds according to the manufacturer's recommendations is not sufficient to ensure complete polymerization. The implications of this incomplete polymerization are discussed in terms of possible cytotoxic effects on tissues exposed to unpolymerized Cavalite, both when used in retrofilling situations and as a deep cavity liner.

Acrylic Resins↗

PubMed1984

Cathepsin D-mediated processing of procollagen: lysosomal enzyme involvement in secretory processing of procollagen.

The proteolytic removal of the extension COOH-terminal propeptide from procollagen has been examined in vitro. A crude enzyme activity was identified in a whole-chicken-embryo extract that acted at acid pH and appeared to be similar to one identified previously [Davidson, J. M., McEneany , L. S. G. & Bornstein , P. (1979) Eur. J. Biochem. 100, 551-558]. This activity was inhibitable by pepstatin but not by leupeptin, suggesting that it might be cathepsin D. Cathepsin D was purified 907-fold from chicken livers by affinity chromatography on pepstatin-aminohexyl-Sepharose 4B and was found to remove the COOH propeptides from procollagen. At pH 6.0, the site of cleavage appeared to shift from the COOH telopeptide to the COOH telopeptide/propeptide junction, based upon the difference in electrophoretic migration of the cleavage products, although determining the actual cleavage site will require end-group analysis. A model for the involvement of cathepsin D in the in vivo processing of procollagen is presented.

Amino Acid Sequence↗

PubMed1981

Collagen self-assembly in vitro. Differentiating specific telopeptide-dependent interactions using selective enzyme modification and the addition of free amino telopeptide.

The thermally induced in vitro self-assembly of collagen molecules to form active fibrils illustrates that collagen molecules themselves contain all of the structural information necessary for assembly. The molecule contains three structural domains, the NH2 and carboxyl-terminal extra helical regions (the telopeptides) and the major triple helical rod-like domain. Proteolytic removal of the short telopeptide domains drastically alters the in vitro self-assembly process. We have examined the specific contributions of each telopeptide to the initiation ("nucleation") and growth stages of self-assembly in collagens modified by selective proteinase treatment and by isolating a peptide containing the amino telopeptide and adding this to both normal and proteinase-modified collagen self-assembly systems. Pronase-modified collagen, devoid of both telopeptides, initiated self-assembly very poorly. Addition of small amounts of intact collagen accelerated the rate of nucleation of pronase-modified collagen. Addition of carboxypeptidase-modified collagen also accelerated the nucleation of pronase-modified collagen, suggesting that the remaining amino telopeptide was involved in nucleation. This was confirmed by isolating the cyanogen bromide fragment of the alpha 1(I) subunit containing the amino telopeptide and finding that it specifically accelerated the nucleation of intact pepsin- and pronase-modified to collagens. The amino telopeptide appears to bind to a specific region within the collagen triple helical domain. The isolated peptide requires thermal pretreatment to be active; hence, this interaction must involve a unique telopeptide conformation. This behavior is compatible with the recent model (Helseth, D. L., Jr., Lechner, J. H., and Veis, A. (1979) Biopolymers 18, 3005-3014) proposed for the conformation of the amino telopeptide and its interaction with a helical receptor site as a step in nucleation. Comparison of the behavior of leucine aminopeptidase- and carboxypeptidase-modified collagens suggests that the carboxyl telopeptide has its major role in the growth stages of self-assembly.

Animals↗

PubMed1976

On using cis-Pt (II)-uracil as a stain for nucleic acids in brain slices and subcellular fractions.

Chick brain cortical slices and crude mitochondrial fractions were fixed with glutaraldehyde, stained only with cis-Pt (II)-uracil and processed for electron microscopy. The optimal time of staining was determined to be 10 min. Results show that this platinum-pyrimidine complex is a relatively specific stain for the nucleic acids of brain slices. However, staining of crude mitochondrial fractions apparently resulted in some protein staining and other artifacts. The method should be helpful identifying ribosomal contamination of subcellular preparations and if its specificity can be increased it may prove a useful addition to staining methods of the electron microscopist.

Animals↗

PubMed1976

Preparation of chick brain synaptosomes and synaptosomal membranes.

A method is described for the preparation of synaptosomes and synaptosomal membranes from chicken brain. Procedures for isolating rat synaptosomal membranes could not be used directly; several modifications of existing procedures are reported. Purity of the subcellular and subsynaptosomal fractions was monitored by electron microscopy and measurements of ferrocytochrome c: oxygen oxidoreductase (EC 1.9.3.)), monoamine: oxygen oxidoreductase (deaminating) EC 1.4.3.4), rotenone-insensitive NADH: cytochrome c oxidoreductase (EC 1.6.99.3), NADPH: cytochrome c oxidoreductase (EC 1.6.99.1), orthophosphoric monoester phosphohydrolase (EC 3.1.3.2), ATP phosphohydrolase (EC 3.6.1.4), and levels of RNA. Microsomes are the main contaminant of the synaptosomal membrane fraction. Mitochondrial and lysosomal enzymes occur in lesser amounts. No myelin contamination was observed. Marker enzymes for contaminants suggest that these synaptosomal membranes are as pure as membranes described by others, and the specific activity of a neuronal membrane marker, (Na+ -K+)-activated ATPase, is as high as other preparations. Levels of this enzyme in the membrane fraction are enriched 13-fold over homogenate ATPase levels.

Animals↗