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Biomedical subjects

E P Katz

Publications and source records attributed to E P Katz.

At least 19 recordsLinked to original sources
PubMed1998

Altered posttranslational modifications of collagen in keloid.

Keloid is a tissue with an excessive accumulation of collagen. In this study, we have partially characterized post-translational modifications of type I collagen in human keloid in order to pursue their potential involvement in this pathology. The levels of lysyl hydroxylation of the helical portions of alpha 1 and alpha 2 chains of type I collagen in keloid were significantly higher than those of normal, while the levels of prolyl hydroxylation were identical between these two groups. The contents of the major reducible cross-links in dermal collagen, dehydro-hydroxylysinonorleucine and dehydro-histidinohydroxymero-desmosine, were both significantly higher in keloids (up to sixfold) than those of normal. In addition, significant amounts of hydroxylysine-aldehyde derived cross-links that are characteristic of skeletal tissue collagens, dehydro-dihydroxylysinonorleucine (about 0.3 mole/mole of collagen) and pyridinoline (about 0.1 mole/mole of collagen), were found in keloids. These results indicate that keloid-forming cells are phenotypically different from those in normal dermis and that the collagen produced is highly cross-linked. The increased cross-linking provides the fibrils with more stability that may result in an accumulation of collagen.

Adult↗
PubMed1996

Cross-linking and the molecular packing of corneal collagen.

We have quantitatively characterized, for the first time, the cross-linking in bovine cornea collagen as a function of age. The major iminium reducible cross-links were dehydro-hydroxylysinonorleucine (deH-HLNL) and dehydro-histidinohydroxymerodesmosine (deH-HHMD). The former rapidly diminished after birth; however, the latter persisted in mature animals at a level of 0.3 - 0.4 moles/mole of collagen. A nonreducible cross-link, histidinohydroxylysinonorleucine (HHL), previously found only in skin, was also found to be a major mature cross-link in cornea. The presence of HHL indicates that cornea fibrils have a molecular packing similar to skin collagen. However, like deH-HHMD, the HHL content in corneal fibrils only reaches a maximum value with time about half that of skin. These data suggest that the corneal fibrils are comprised of discrete filaments that are internally stabilized by HHL and deH-HHMD cross-links. This pattern of intermolecular cross-linking would facilitate the special collagen swelling property required for corneal transparency.

Aging↗
PubMed1993

The post-translational chemistry and molecular packing of mineralizing tendon collagens.

Using cross-linking stereochemistry as indicators, the molecular environment of two collagens in the turkey leg Achilles tendon were compared. The tendon from one year old turkeys was dissected into nonmineralized, fully mineralized and transitionally mineralized portions. Amino acid composition and cyanogen bromide peptide mapping of these portions indicated that the collagens were essentially type I throughout. The fully mineralized compartment had a lysine hydroxylation level similar to turkey or mammalian bone collagen. The non- and transitionally mineralized collagens had a significantly higher lysine hydroxylation, typical of tendon or ligament. However, unlike mammalian tendon, the collagen cross-links were essentially derived from the carboxy-terminal ends of the molecules. The predominant cross-link in this portion was pyridinoline having a high content of 0.95 +/- 0.09 res/mole of collagen. The cross-links in the fully mineralized collagen were also essentially derived from carboxy-terminal aldehyde. However, here significant amounts of the lysyl analog of pyridinoline and lysine-involved bifunctional cross-links were present. The molecular loci of pyridinoline in nonmineralized collagen and the lysyl analog of pyridinoline in mineralized collagen were found to be identical. The total trifunctional cross-link level in the mineralized collagen, 0.55 +/- 0.05 res/mole of collagen, was virtually identical to that observed in old mammalian bone and dentin, and in long term in vitro incubation studies of predentin. We have tentatively concluded that the post-translational chemistry and molecular environments are different in these two turkey tendon fibrils. However, a relative paucity of amino-terminal based cross-links is a feature they have in common. The possible involvement of the amino-terminal telopeptides in collagen mineralization is discussed.

Amino Acids↗
PubMed1992

Unique side-chain conformation encoding for chirality and azimuthal orientation in the molecular packing of skin collagen.

We used molecular mechanics to study the role of gly X-Y+ sequences, where X- was Asp or Glu and Y+ was Lys or Arg, in the molecular packing of type I collagen. In the minimal energy conformation of a triply stranded molecule having a coiled-coil configuration, the side-chains of these sequences segregated into two oppositely charged groupings of the forms X-Y+X- and Y+X-Y+. Groupings having the same net charge were clustered along two complementary azimuthal edges of the molecule. Intermolecular interactions, through these oppositely charged edges, align the molecules appropriately for the formation of the HHL crosslink of skin. This alignment also can account for the axial periodicity and chiral appearance of skin collagen fibrils.

Amino Acid Sequence↗
PubMed1992

Cross-linking connectivity in bone collagen fibrils: the COOH-terminal locus of free aldehyde.

Quantitative analyses of the chemical state of the 16c residue of the alpha 1 chain of bone collagen were performed on samples from fetal (4-6-month embryo) and mature (2-3 year old) bovine animals. All of this residue could be accounted for in terms of three chemical states, in relative amounts which depended upon the age of the animal. Most of the residue was incorporated into either bifunctional or trifunctional cross-links. Some of it, however, was present as free aldehyde, and the content increased with maturation. This was established by isolating and characterizing the aldehyde-containing peptides generated by tryptic digestion of NaB3H4-reduced mature bone collagen. We have concluded that the connectivity of COOH-terminal cross-linking in bone collagen fibrils changes with maturation in the following way: at first, each 16c residue in each of the two alpha 1 chains of the collagen molecule is incorporated into a sheet-like pattern of intermolecular iminium cross-links, which stabilizes the young, nonmineralized fibril as a whole. In time, some of these labile cross-links maturate into pyridinoline while others dissociate back to their precursor form. The latter is likely due to changes in the molecular packing brought about by the mineralization of the collagen fibrils. The resultant reduction in cross-linking connectivity may provide a mechanism for enhancing certain mechanical characteristics of the skeleton of a mature animal.

Aldehydes↗
PubMed1991

The effect of osmotic and mechanical pressures on water partitioning in articular cartilage.

X-ray diffraction measurements on native and proteoglycan-free articular cartilage have been made in order to test the dependence of the lateral packing of the collagen molecules on the osmotic pressure gradient, either naturally occurring or externally applied, between the intra- and extrafibrillar compartments. From the information on collagen packing we have been able to calculate, albeit with several assumptions, the amount of intrafibrillar water as a function of pressure. In parallel with the above measurements, we have quantitated, using serum albumin partitioning, the intrafibrillar water in proteoglycan-free cartilage, as a function of mechanically applied pressure. The results of both sets of experiments lead to the conclusion that the molecular packing density, and hence the intrafibrillar water content, are a function of the osmotic pressure difference between the extrafibrillar and intrafibrillar spaces or the equivalent mechanically applied pressure. The determination of intrafibrillar water has enabled us to calculate, from measured values of fixed charge density, the internal osmotic pressure of cartilage specimens, both in compressed and uncompressed states.

Adult↗
PubMed1991

On the adaptive structures of the collagen fibrils of bone and cartilage.

In order to investigate how bone and cartilage respond at the molecular level to changing demands of the skeleton, the influence of endogenous and external chemical stresses on collagen fibrillar structure as a function of locale in the femoral articular cartilage from 2 to 14 year old cows has been studied by x-ray diffraction. The fibrils were found to be osmotically compressed by vicinal proteoglycans. For most locales, the molecular packing density was less at the articular surface and increased to a maximum adjacent to the bone. This gradient in structure became more accentuated with animal age. For all ages, the packing density gradients could be almost completely eliminated upon enzymatic removal of the proteoglycans. However, in the regions of cartilage which had experienced the greatest stress in locomotion, the fibrils had a hyperswollen structure. This tendency towards hyperswelling increased with animal age. We have concluded that the collagen fibrils in articular cartilage adapt a structure that is in response to their respective mechanico-chemical histories.

Adaptation, Physiological↗
PubMed1990

Regional distribution of mineral and matrix in the femurs of rats flown on Cosmos 1887 biosatellite.

We combined biochemical measurements with novel techniques for image analysis in the rat femur to characterize the location and nature of the defect in mineralization known to occur in growing animals after spaceflight. Concentrations of mineral and osteocalcin were low in the distal half of the diaphysis and concentrations of collagen were low with evidence of increased synthesis in the proximal half of the diaphysis of the flight bones. X-ray microtomography provided semiquantitative data in computer-generated sections of whole wet bone that indicated a longitudinal gradient of decreasing mineralization toward the distal diaphysis, similar to the chemistry results. Analysis of embedded sections by backscattered electrons in a scanning electron microscope revealed distinct patterns of mineral distribution in the proximal, central, and distal regions of the diaphysis and also showed a net reduction in mineral levels toward the distal shaft. Increases in mineral density to higher fractions in controls were less in the flight bones at all three levels, with the most distal cross-sectional area most affected. The combined results from these novel techniques identified the areas of femoral diaphysis most vulnerable to the mineralization defect associated with spaceflight and/or the stress of landing.

Animals↗
PubMed1989

The structure of mineralized collagen fibrils.

A new model for the structure of mineralized bone collagen is presented which is compatible with neutron diffraction, electromicroscopic, crosslinking, and composition-density data. Mineralized collagen fibrils are comprised of azimuthally oriented, flexible molecules laterally arranged on a superlattice. Four nearest neighbors are longitudinally staggered by 67 nm and two neighbors by 2* 67 nm. In early stages of mineralization the molecules are parallel to the fibril axis with an average interaxis distance of 1.8 nm. In later stages they become flexed away from the fibril axis by an anisotropic lateral compression of molecules to an interaxis distance of 1.3 nm. Three quarters of the mineral in bone is disposed within the fibrils with a symmetry and habit reflecting the above organization of the collagen molecules.

Calcification, Physiologic↗
PubMed1989

Cross-linking and stereospecific structure of collagen in mineralized and nonmineralized skeletal tissues.

Molecular distributions of the intermolecular cross-links in fetal bovine bone type I collagen fibrils were quantitatively determined and compared with those of periodontal ligament. Results indicated that Hyl and Lys residues in the COOH-terminal nonhelical peptide portions (residues 16C) of both alpha 1 chains were quantitatively converted to aldehydes. These in turn stoichiometrically formed cross-links with residues Hyl-87 on both alpha 1 and alpha 2 chains of neighboring molecules. The ratio of cross-linked alpha 1 to alpha 2 chains was 3.5 to 1 indicating a stereospecific packing of collagen molecules in the fibrils similar manner to periodontal ligament collagen. It was found that there were few aldehyde derived cross-links in the NH2-terminal nonhelical portions of the bone type I collagen. The relative paucity of the cross-links in NH2-terminal region of bone collagens may favor mineralization.

Animals↗
PubMed1987

Locus of a histidine-based, stable trifunctional, helix to helix collagen cross-link: stereospecific collagen structure of type I skin fibrils.

The loci of the three amino acid residues that contribute their prosthetic groups to form the stable, nonreducible, trifunctional intermolecular cross-link histidinohydroxylysinonorleucine in skin collagen fibrils were identified. Two apparently homogeneous three-chained histidinohydroxylysinonorleucine cross-linked peptides were chromatographically isolated. They were obtained from a tryptic digest of denatured unreduced 6 M guanidine hydrochloride insoluble bovine skin collagen. Amino acid and sequence analyses demonstrated that the prosthetic groups of alpha 1(I)-chain Hyl-87, alpha 1(I)-chain Lys-16c, and alpha 2(I)-chain His-92 formed the cross-link. The latter results served to define the locus of the stable, nonreducible trifunctional moiety. Identical types of analyses were performed on the three-chained peptides isolated after bacterial collagenase digestion of the cross-linked tryptic peptides. This confirmed the initial identification and location of the three peptides linked by the cross-link. In addition, data reported here provide for a correction of the micromolecular structure for the alpha 2(I) chain. Stereochemical considerations concerning this trifunctional cross-link's specific locus indicate that the steric relationships between the alpha chains of skin and skeletal tissue collagens are fundamentally different and the intermolecular relationships in skin fibrils are specific for skin. The same molecular relationships also indicate that histidinohydroxylysinonorleucine links three molecules of collagen. The stereochemistry of cross-linking for skin collagen is in accordance with and explains the X-ray findings of a 65-nm periodicity found for this tissue [Stinson, R. H., & Sweeny, P. R. (1980) Biochim. Biophys. Acta 621, 158; Brodsky, B., Eikenberry, E. F., & Cassidy, K. (1980) Biochim. Biophys. Acta 621, 162].

Amino Acid Sequence↗
PubMed1986

Intermolecular cross-linking and stereospecific molecular packing in type I collagen fibrils of the periodontal ligament.

A trypsin digest of denatured NaB3H4-reduced native bovine periodontal ligament was prepared and fractionated by gel filtration and cellulose ion-exchange column chromatography. Prior to trypsin digestion, a complete acid hydrolysate was subjected to analyses for nonreducible stable and reducible intermolecular cross-links. Minute amounts of the former and significant amounts of the reduced cross-links dihydroxylysinonorleucine (1.1 mol/mol of collagen), hydroxylysinonorleucine (0.9 mol/mol of collagen), and histidinohydroxymerodesmosine (0.6 mol/mol of collagen) were found. The covalent intermolecular cross-linked two-chained peptides that were isolated were subjected to amino acid and sequence analyses. The structures for the different two-chained linked peptides were alpha 1CB4-5(76-90)[Hyl-87] X alpha 1CB6-(993-22c)[Lysald-16c], alpha 1CB4-5(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Hylald-16c], alpha 2CB4(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Lysald-16c], and alpha 2CB4(76-90)[Hyl-87] X alpha 1CB6(993-22c)[Hylald-16c]. The cross-link in each peptide was glycosylated. This is the first characterization by sequence analysis of a cross-link involving Hyl-87 in an alpha 2 chain in collagen. A stoichiometric conversion of residue 16c aldehyde to an intermolecular cross-link in each of the COOH-terminal nonhelical peptide regions of both alpha 1 chains in a molecule of type I collagen was found. The ratio of alpha 1 to alpha 2 intermolecularly cross-linked chains involved was 3.3:1, indicating a stereospecific three-dimensional molecular packing of type I collagen molecules in bovine periodontal ligament.

Amino Acid Sequence↗
PubMed1977

On the state of anionic groups of demineralized matrices of bone and dentine.

Calcium-binding and biochemical studies have been applied to characterize the state of the carboxylate and protein-bound phosphate groups in the EDTA-demineralized matrices of rat bone and dentine. The organic phosphate and carboxylate content of demineralized bone is virtually identical to that of purified steer skin collagen whereas demineralized dentine has a significantly higher phosphate and carboxylate content, presumably due to the presence of an acidic non-collagenous phosphoprotein. Two classes of calcium-binding sites can be detected in demineralized bone, demineralized dentine, and purified, reconstituted collagen. The number of strong calcium-binding sites correlates with the number of protein-bound phosphate groups. Depending on the preparative procedure, seven to nine such sites (per collagen molecule) are present in dentine, and one to two in the purified reconstituted collagen and in bone. The binding constant for the dentinal sites (1.1 X 10(4) M-1), however, is 20 times greater than that for bone or reconstituted collagen fibrils from skin. We tentatively conclude that the strong calcium-binding site in bone and reconstituted collagen is of the form protein-PO-4Ca++ whereas in dentine it is of the form protein (formula: see text); the weak binding sites in bone and dentine are of the form protein-COO-Ca++; and that approximately 160 of the 217 carboxylate groups of the collagen molecules of dentine or bone are present as electrostatic linkages of the form protein-COO-+H3N-protein.

Animals↗