Further studies on the effect of the collagen triple-helix formation on the hydroxylation of lysine and the glycosylations of hydroxylysine in chick-embryo tendon and cartilage cells

The hydroxylation of lysine and glycosylations of hydroxylysine were studied in isolated chick-embryo tendon and cartilage cells under conditions in which collagen triple-helix formation was either inhibited or accelerated. The former situation was obtained by incubating the tendon cells with 0.6mm-dithiothreitol, thus decreasing their proline hydroxylase activity by about 99%. After labelling with [(14)C]proline, the formation of hydroxy[(14)C]proline was found to have declined by about 95%. Since the hydroxylation of a relatively large number of proline residues is required for triple-helix formation at 37 degrees C, the pro-alpha-chains synthesized under these conditions apparently cannot form triple-helical molecules. Labelling experiments with [(14)C]lysine indicated that the degree of hydroxylation of the lysine residues in the collagen synthesized was slightly increased and the degree of the glycosylations of the hydroxylysine residues more than doubled, the largest increase being in the content of glucosylgalactosylhydroxylysine. Recovery of chick-embryo cartilage cells from temporary anoxia was used to obtain accelerated triple-helix formation. A marked decrease was found in the extent of hydroxylation of the lysine residues in the collagen synthesized under these conditions, and an even larger decrease occurred in the glycosylations of the hydroxylysine residues. The results support the previous suggestion that the triple-helix formation of the pro-alpha-chains prevents further hydroxylation of lysine residues and glycosylations of hydroxylysine residues during collagen biosynthesis.     

Stimulation of hepatic biogenesis of sterols on administration of adenosine compounds.

The glycosylations of hydroxylysine during collagen biosynthesis in isolated chick-embryo tendon cells were studied by using pulse-chase labelling experiments with [14C]-lysine. The hydroxylation of lysine and the glycosylations of hydroxylysine continued after a 5 min pulse label for up to about 10 min during the chase period. These data differ from those obtained previously in isolated chick-embryo cartilage cells, in which, after a similar 5 min pulse label, these reactions continued during the chase period for up to about 20 min. The collagen synthesized by the isolated chick-embryo tendon cells differed markedly from the type I collagen of adult tissues in its degree of hydroxylation of lysine residues and glycosylations of hydroxylysine residues. When the isolated tendon cells were incubated in the presence of L-azetidine-2-carboxylic acid, the degree of glycosylations of hydroxylysine during the first 10 min of the chase period was identical with that in cells incubated without thcarboxylic acid for at least 60 min, whereas no additional glycosylations took place in the control cells after the 10 min time-point. As a consequence, the collagen synthesized in the presence of this compound contained more carbohydrate than did the collagen synthesized by the control cells. Additional experiments indicated that azetidine-2-carboxylic acid did not increase the collagen glycosyltransferase activities in the tendon cells or the rate of glycosylation reactions when added directly to the enzyme incubation mixture. Control experiments with colchicine indicated that the delay in the rate of collagen secretion, which was observed in the presence of azetidine-2-carboxylic acid, did not in itself affect the degree of glycosylations of collagen. The results thus suggest that the increased glycosylations were due to inhibition of the collagen triple-helix formation, which is known to occur in the presence of azetidine-2-carboxylic acid.     

The isolation, and amino acid and carbohydrate composition, of polymeric collagens prepared from various human tissues

1. Insoluble polymeric collagens from various human tissues were prepared by the EDTA method. Almost all of the collagen from simple soft tissues such as dermis, tendon, submucosa, sclera and cornea could be extracted, whereas the more complex tissues such as intercostal cartilage and intervertebral disc yielded only small amounts of collagen. Amino acid and carbohydrate analysis indicated that most of the preparations were highly purified on the basis of their tyrosine, hexosamine, mannose, xylose and fucose contents. 2. Wide variation in the total hexose content was observed, the lowest being 8.5 residues/3000 amino acid residues for collagen from dermis and the highest being 42.1 residues/3000 in corneal collagen. The molar ratios of sugars also varied, submucosal collagen having a galactose/glucose ratio of 1.0 and corneal collagen having a ratio of 2.3. 3. The presence of glucosylgalactosylhydroxylysine was confirmed in submucosal collagen by compositional and chromatographic analysis of this component after its isolation from alkaline hydrolysates of the collagen. Evidence was also obtained for the presence of galactosylhydroxylysine. 4. Determination of the hydroxylysyl glycosides was carried out and it was observed that the amounts of these components varied widely from tissue to tissue. Corneal collagen contained 19.1 hydroxylysine-linked carbohydrate units/3000 amino acid residues, whereas tendon collagen contained only 4.1 units/3000. Variation in the ratio disaccharide unit/monosaccharide unit was also observed, the ratio being 1.2 in intercostal cartilage collagen and 4.1 in submucosal collagen. The proportion of the total hydroxylysine that was substituted by carbohydrate also varied from tissue to tissue.     

Phagocytosis of collagen fibrils by periosteal fibroblasts in long bone explants. Effect of concanavalin A

In an attempt to determine whether phagocytosis of collagen by fibroblasts involves binding of the fibril to the plasma membrane, the effect of the lectin concanavalin A (Con A) was studied in an in vitro model system. Metacarpal bone rudiments from 19-day-old mouse fetuses were incubated with varying concentrations of the lectin. Quantitative electron microscopic analysis indicated that Con A caused a dose-related increase in the amount of phagocytosed collagen fibrils in periosteal fibroblasts, suggesting either an enhanced uptake or a decreased intracellular breakdown of fibrils. Since a Con A-inducible increase was not seen in the combined presence of both the lectin and the proteinase inhibitor leupeptin, which is known to inhibit the intracellular digestion of phagocytosed fibrillar collagen, it is unlikely that Con A stimulated phagocytosis. Based on the finding that Con A interfered with the digestion of a synthetic substrate by the collagenolytic lysosomal enzyme cathepsin B it is suggested that the augmentation of intracellular fibrillar collagen under the influence of the lectin was due to a decreased intracellular digestion. Since Con A did not inhibit the uptake of collagen fibrils by the fibroblasts it is concluded that Con A-inhibitable binding sites for collagen molecules are unlikely to be involved in phagocytosis of collagen fibrils by fibroblasts.     

Immunohistochemical study of collagens of the extracellular matrix in cartilage of Sepia officinalis

We used various anti-collagen antibodies to perform indirect immunofluorescent staining of cartilage sections from cuttlefish (S. officinalis). On ultrathin sections and collagen fibril preparations from the same tissue, we performed immunostaining with colloidal gold. The extracellular matrix (ECM) of S. officinalis cartilage reacted intensely and homogeneously with an antibody directed against type I-like collagen isolated from the cartilage of cuttlefish and with anti-rat type V collagen antibody. A weak reaction was observed with anti-fish and anti-chicken type I collagen antibodies, while no reaction was observed with anti-rat type I and anti calf type II collagen antibodies. Anti-chicken type II, anti calf type IX and type XI collagen antibodies reacted weakly with ECM, while stained cell bodies and cell processes reacted more intensely. A similar pattern of reaction was observed on cartilage section and isolated collagen fibrils prepared for electron microscopy. These findings suggest that ECM of cuttlefish cartilage may be composed of molecules similar to the type I, type V, type IX and type XI collagen molecules of vertebrates. Cephalopods have evolved a cartilage of structure and macromolecular organisation similar to that of vertebrate cartilage. However, the main molecular components of S. officinalis cartilage--type I-like and type V collagens--differ from those of vertebrate cartilage. We suggest that this type I-like collagen can be considered an initial step toward the evolution of type II collagen typical of vertebrates.     

Pyridinoline, a non-reducible crosslink of collagen. Quantitative determination, distribution, and isolation of a crosslinked peptide

Pyridinoline is a crosslink compound isolated from bovine Achilles tendon collagen. It is a 3-hydroxypyridinium derivative with three amino and three carboxyl groups (Fujimoto, D., Akiba, K., & Nakamura, N. (1977) Biochem. Biophys. Res. Commun. 76, 1124-1129). The contents of pyridinoline in collagens from various sources were determined. The pyridinoline content of bovine Achilles tendon was 0.16 residue per 1,000 residues and that of rat Achilles tendon collagen was 0.017 residue per 1,000 residues. Besides Achilles tendon collagens, pyridinoline was found in collagens from costal cartilage, rib and femoral bone of rat. It was not found in collagens from the tail tendon and skin of rat. A crosslinked, triple-chained peptide containing pyridinoline was isolated from bovine Achilles tendon collagen after digestion with pronase. Its amino acid composition suggests that the peptide may be involved in an intermolecular crosslink among a carboxyterminal sequence, a sequence near the aminoterminus and a sequence in the helical region.     

COMP acts as a catalyst in collagen fibrillogenesis

We have previously reported that COMP (cartilage oligomeric matrix protein) is prominent in cartilage but is also present in tendon and binds to collagens I and II with high affinity. Here we show that COMP influences the fibril formation of these collagens. Fibril formation in the presence of pentameric COMP was much faster, and the amount of collagen in fibrillar form was markedly increased. Monomeric COMP, lacking the N-terminal coiled-coil linker domain, decelerated fibrillogenesis. The data show that stimulation of collagen fibrillogenesis depends on the pentameric nature of COMP and not only on collagen binding. COMP interacts primarily with free collagen I and II molecules, bringing several molecules to close proximity, apparently promoting further assembly. These assemblies further join in discrete steps to a narrow distribution of completed fibril diameters of 149 +/- 16 nm with a banding pattern of 67 nm. COMP is not found associated with the mature fibril and dissociates from the collagen molecules or their early assemblies. However, a few COMP molecules are found bound to more loosely associated molecules at the tip/end of the growing fibril. Thus, COMP appears to catalyze the fibril formation by promoting early association of collagen molecules leading to increased rate of fibrillogenesis and more distinct organization of the fibrils.     

Glutaraldehyde-induced changes in the axially projected fine structure of collagen fibrils

The fine structure of the collagen fibril, as seen in axial projection, is changed by treatment with glutaraldehyde. The changes are detectable in electron-optical staining patterns and in the intensities of the low-angle meridional X-ray diffraction maxima. Current knowledge of the amino acid sequence of collagen and of the axial arrangement of molecules in fibrils permits interpretation in terms of specific alterations to the axial distribution of electron density along the fibril. Analysis of fibril staining patterns from glutaraldehyde-treated calf skin collagen shows that uptake of staining ions in positive staining patterns is inhibited at residues known to interact with glutaraldehyde (lysyl, hydroxylysyl and probably histidyl side-chains) and on other charged residues in the immediate neighbourhood of the glutaraldehyde-reactive residues. This can be seen as a "stain-exclusion effect" due to the presence of bulky polymeric complexes of glutaraldehyde molecules at cross-linking sites. Such stain exclusion accounts for the drastic changes in the negative staining pattern following treatment with glutaraldehyde. The intensity changes observed in the low-angle meridional X-ray reflections from rat tail tendon, similarly treated, also can be explained by the presence of these bulky complexes. Existing data have been used to predict a model of the altered electron density profile indicating the axial distribution of glutaraldehyde along a D-period of moist tendon collagen.     

Differential localization of mRNAs of collagen types I and II in chick fibroblasts, chondrocytes, and corneal cells by in situ hybridization using cDNA probes

We have employed a highly specific in situ hybridization protocol that allows differential detection of mRNAs of collagen types I and II in paraffin sections from chick embryo tissues. All probes were cDNA restriction fragments encoding portions of the C-propeptide region of the pro alpha-chain, and some of the fragments also encoded the 3'-untranslated region of mRNAs of either type I or type II collagen. Smears of tendon fibroblasts and those of sternal chondrocytes from 17-d-old chick embryos as well as paraffin sections of 10-d-old whole embryos and of the cornea of 6.5-d-old embryos were hybridized with 3H-labeled probes for either type I or type II collagen mRNA. Autoradiographs revealed that the labeling was prominent in tendon fibroblasts with the type I collagen probe and in sternal chondrocytes with the type II collagen probe; that in the cartilage of sclera and limbs from 10-d-old embryos, the type I probe showed strong labeling of fibroblast sheets surrounding the cartilage and of a few chondrocytes in the cartilage, whereas the type II probe labeled chondrocytes intensely and only a few fibroblasts; and that in the cornea of 6.5-d-old embryos, the type I probe labeled the epithelial cells and fibroblasts in the stroma heavily, and the endothelial cells slightly, whereas the type II probe labeled almost exclusively the epithelial cells except for a slight labeling in the endothelial cells. These data indicate that embryonic tissues express these two collagen genes separately and/or simultaneously and offer new approaches to the study of the cellular regulation of extracellular matrix components.     

Lectin binding to collagen strands in histologic tissue sections

Histologic sections from human skin and uterine ligaments were stained with the following FITC conjugated lectins: Con A, WGA, s-WGA, SBA, DBA, UEA I, PNA, RCA I, BPA, GSA I, GSA II, MPA and LPA. The staining of the connective tissue was similar in the dermis and the uterine ligaments and it was most intense in the extracellular matrix containing collagen strands whereas the fibrocytes remained unstained. The staining was clear with glucose or N-acetylglucosamine binding lectins like Con A, WGA, s-WGA and GSA II, which may be related to the presence of glucose residues in collagenous hydroxylysine. The staining with some of the galactose or N-acetylgalactosamine binding lectins like RCA I, DBA, and BPA was less intense. This may reflect the presence of terminal galactose sugars in the hydroxylysine of collagen. No staining was found with SBA, UEA I, PNA, GSAI, MPA or LPA. The results show that different particularly glucose specific lectins bind to the extracellular matrix and especially to collagenous strands in connective tissue. It is suggested that this might be used in histochemical studies of connective tissue and particularly concerning the changes that may occur in different disease states.     

Changes in the structure of neuromuscular junctions caused by variations in osmotic pressure

Reconstituted cartilage collagen fibrils with an oblique banding pattern or with two types of symmetrical patterns, and reconstituted rattail tendon fibrils with a third type of symmetrical pattern were examined by electron microscopy and found to consist of narrow subfibrils having native-type cross-striations. Analysis of the four types of patterns by a graphic method of specific band matching revealed the orientation and axial relation of individual subfibrils and their component molecules. In fibrils with an oblique pattern, subfibrils have the same orientation and a regular 100A axial displacement. Observations on staining characteristics, folded fibrils, and transverse sections of embedded fibrils suggest that the obliquely banded fibrils are ribbonlike or layered structures. In the three types of fibrils with a symmetrical pattern, adjacent subfibrils are oppositely oriented and aligned within a 119-A segment of the 670-A major period. Considered together, the observations suggest that interaction sites on the surface of subfibrils (and perhaps on the surface of native collagen fibrils) occur in various patterns that are manifested accouding to the nature of the environment during fibril formation, and that such patterns can be mapped on the surface of subfibrils by noting the arrangement of subfibrils in polymorphic forms.     

Hysteretic kinetic behavior of beef liver pyruvate carboxylase.

Natural abundance ¹³C nuclear magnetic resonance (nmr) spectra have been obtained for samples of a variety of native collagens by use of cross-polarization (CP) techniques which permit high resolution natural abundance ¹³C nmr spectra of solids to be obtained with high sensitivity. The CP ¹³C nmr spectra of lyophilized skin and tendon collagens consisted of two broad resonance envelopes spanning a five kHz range. Hydrated tendon collagen gave rise to a CP spectrum very similar to that obtained for the lyophilized sample, indicating that it retains its solid-like properties. In contrast, hydrated skin collagen became denatured under the conditions of the CP experiment and subsequently gave rise to a conventional high-resolution Fourier transform (FT) nmr spectrum. The CP ¹³C nmr spectrum of ivory was similar to those of lyophilized skin and tendon collagens, demonstrating the solid-like character of the collagen in dentine, whereas the CP spectrum of bovine nasal cartilage reflected the presence of highly mobile proteoglycan components in addition to relatively rigid collagen molecules. In the case of ivory, the resolution of the CP spectrum was enhanced by “magic angle” spinning to a degree approaching that of conventional FT ¹³C nmr spectra of denatured collagen in solution. Because of its ability to probe the dynamic properties of solid-like biological molecules, CP ¹³C nmr spectroscopy should be a valuable investigative tool for future studies.     

Evolutionary Origins of C-Terminal (GPP)n 3-Hydroxyproline Formation in Vertebrate Tendon Collagen

Approximately half the proline residues in fibrillar collagen are hydroxylated. The predominant form is 4-hydroxyproline, which helps fold and stabilize the triple helix. A minor form, 3-hydroxyproline, still has no clear function. Using peptide mass spectrometry, we recently revealed several previously unknown molecular sites of 3-hydroxyproline in fibrillar collagen chains. In fibril-forming A-clade collagen chains, four new partially occupied 3-hydroxyproline sites were found (A2, A3, A4 and (GPP)_n) in addition to the fully occupied A1 site at Pro986. The C-terminal (GPP)_n motif has five consecutive GPP triplets in α1(I), four in α2(I) and three in α1(II), all subject to 3-hydroxylation. The evolutionary origins of this substrate sequence were investigated by surveying the pattern of its 3-hydroxyproline occupancy from early chordates through amphibians, birds and mammals. Different tissue sources of type I collagen (tendon, bone and skin) and type II collagen (cartilage and notochord) were examined by mass spectrometry. The (GPP)_n domain was found to be a major substrate for 3-hydroxylation only in vertebrate fibrillar collagens. In higher vertebrates (mouse, bovine and human), up to five 3-hydroxyproline residues per (GPP)_n motif were found in α1(I) and four in α2(I), with an average of two residues per chain. In vertebrate type I collagen the modification exhibited clear tissue specificity, with 3-hydroxyproline prominent only in tendon. The occupancy also showed developmental changes in Achilles tendon, with increasing 3-hydroxyproline levels with age. The biological significance is unclear but the level of 3-hydroxylation at the (GPP)_n site appears to have increased as tendons evolved and shows both tendon type and developmental variations within a species.     

Localization of a dermatan sulfate proteoglycan (DS-PGII) in cartilage and the presence of an immunologically related species in other tissues

A monoclonal antibody to a core-protein-related epitope of a small dermatan sulfate-rich proteoglycan (DS-PGII) isolated from adult bovine articular cartilage (22) was used to localize this molecule, or molecules containing this epitope, in bovine articular cartilages, in cartilage growth plate, and in other connective tissues. Using an indirect method employing peroxidase-labeled pig anti-mouse immunoglobulin G, DS-PGII was shown to be present mainly in the superficial zone of adult articular condylar cartilage of the metacarpal-phalangeal joint. In fetal articular and epiphyseal cartilages, the molecule was uniformly distributed throughout the matrix. By approximately 10 months of age it was confined mainly to the superficial and middle zones of articular cartilage and the inter-territorial and pericellular matrix of the deep zone. DS-PGII was not detected in the primary growth plate of the fetus except in the proliferative zone, where it was sometimes present in trace amounts. In contrast, it was present throughout the adjacent matrix of developing epiphyseal cartilage. In the trabeculae of the metaphysis, strong staining for DS-PGII was seen in decalcified osteoid and bone immediately adjacent to osteoblasts. Staining was also observed on collagen fibrils in skin, tendon, and ligament and in the adventitia of the aorta and of smaller arterial vessels in the skin. These observations indicate that DS-PGII and/or molecules containing this epitope are widely distributed in collagenous tissues, where the molecule is intimately associated with collagen fibrils; in adult cartilage this association is limited mainly to the narrow parallel arrays of fibrils which are found in the superficial zone at the articular surface. From its intimate association and other studies, this molecule may play an important role in determining the sizes and tensile properties of collagen fibrils; it may also be involved in the calcification of osteoid but not of cartilage.     

Ultrastructural and biochemical identification of con A receptors in the desmosome

Correlated ultrastructural and biochemical methods were used to identify and localize Concanavalin A (Con A) receptors in the desmosomes of bovine epidermis. Specific carbohydrate residues were labeled with ferritin-Con A in thin sections of tissue embedded in a hydrophilic resin. Quantitative mapping of ferritin distribution in labeled desmosomes revealed that Con A receptors are localized in the intercellular zone and concentrated along the desmosomal midline or central dense stratum. Labeling was almost entirely absent when sections were treated with ferritin-Con A in the presence of 0.1 M α-methyl mannoside, a hapten-inhibitor of Con A. “Whole” desmosomes and desmosomal intercellular regions (desmosomal “cores”) were purified from bovine muzzle epidermis. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis reveals a limited number of major desmosomal protein constituents. Certain of these are glycoproteins and are greatly enriched in the core fraction. Almost all the desmosomal glycoproteins are intensely labeled when electrophoretic gels of whole desmosome or core fractions are exposed to fluorescent Concanavalin A.     

Mechanism for the regulation of post-translational modifications of procollagens synthesized by matrix-free cells from chick embryos

Three possible mechanisms are considered to account for the variations of post-translational modifications in different collagen types. 1) The cells have different amounts of post-translational modifying enzymes, 2) the rate of prolylhydroxylation of different procollagen types is varied, and 3) the rate of chain association of pro-alpha chains of different collagen types is modulated. In an attempt to examine the three possibilities, we have determined the activities of prolyl hydroxylase and lysyl hydroxylase, and we have examined the kinetics of the secretion of procollagens and the kinetics of pro-gamma chain formation of different procollagen types in matrix-free cells isolated from tissues of 17-day-old chick embryos. Type II collagen synthesized by cartilage cells contains more hydroxylysine than type I collagen synthesized by tendon and cornea cells. It was found, however, that cartilage cells contain significantly less lysyl hydroxylase than tendon and cornea cells. In contrast, we found only a small difference in the amount of prolyl hydroxylase in tendon, cornea, and cartilage cells. The secretion of type I procollagen by tendon and cornea cells can be described by two first order processes. In contrast, the secretion of type II procollagen by cartilage cells, type IV procollagen by lens cells, and type V procollagen by cornea cells can be described by single first order processes. Examination of the formation of pro-gamma components of procollagen types I and II revealed that it occurs via intermediate dimers of two pro-alpha chains. The formation or pro-gamma(I) chains in tendon and cornea cells is about three times faster than the formation of pro-gamma(II) chains in cartilage cells. These results are consistent with the hypothesis that the rate of association of pro-alpha chains regulates the synthesis of procollagens with different degrees of post-translational modifications.     

Polarization microscopy and microspectrophotometry of Sirius Red, Picrosirius and Chlorantine Fast Red aggregates and of their complexes with collagen

Summary A detailed quantitative analysis of the anisotropic properties of Sirius Red F3B, Picrosirius, and Chlorantine Fast Red crystals, and of their complexes with a macromolecularly oriented protein either in a pure form or as part of a tissue structure was carried out. Collagen I was used as the protein model. Linear dichroism and dispersion of birefringence were investigated in dye aggregates, in stained filaments of collagen I and in collagen bundles in sections of tendon. A positive linear dichroism, the characteristics of which varied as a function of the dye type used, was demonstrated for the dye aggregates and stained substrates. However, even thin regions of the stained tendon collagen bundles showed very high absorbances, differing from the pattern reported previously, for collagen stained with another sulphonated azo dye, Xylidine Ponceau. Consequently, not all these dyes enable protein concentration and orientation to be determined in collagen-containing structures. From the linear dichroism patterns it is assumed that the long axis of the molecules of these azo dye is mostly parallel to that of filaments of pure collagen I and statistically parallel to the long axis of collagen bundles of tendon sections. The dye aggregates and, stained pure collagen I and tendon collagen bundles exhibited birefringent images with interference colours that varied as a function of thickness and packing state of the preparations, which is in agreement with reports in the literature. The optical retardations of the collagen bundles increased by a factor of 5–6 times after staining with Picrosirius. From data on form dichroism it is concluded that when studying the macromolecular orientation of collagen preparations stained with azo dyes, the choice of the mounting medium deserves consideration.     

Specific inhibition of type I and type II collagen fibrillogenesis by the small proteoglycan of tendon.

The small dermatan sulphate proteoglycan of bovine tendon demonstrated a unique ability to inhibit fibrillogenesis of both type I and type II collagen from bovine tendon and cartilage respectively in an assay performed in vitro. None of the other proteoglycan populations from cartilage, tendon or aorta, even those similar in size and chemical structure, had this effect. Alkali treatment of the small proteoglycan of tendon eliminated its ability to inhibit fibrillogenesis, whereas chondroitinase digestion did not. This indicates that its interaction with collagen depends on the core protein. Fibrillogenesis of pepsin-digested collagens was affected similarly, indicating that interaction with the collagen telopeptides is not involved. The results suggest that interactions between collagen and proteoglycans may be quite specific both for the type of proteoglycan and its tissue of origin.     

Isolation and characterization of CNBr peptides of human (alpha 1 (III) )3 collagen and tissue distribution of (alpha 1 (I) )2 alpha 2 and (alpha 1 (III) )3 collagens.

[Alpha 1(III)]3 collagen was solubilized by pepsin digestion of normal human placental membranes and was purified by differential salt precipitation and carboxymethylcellulose chromatography. This collagen was digested with CNBr, and the resultant nine peptides were isolated and characterized. The chains are cross-linked by cysteinyl residues in the COOH-terminal peptide. Isolation of peptides derived from CNBr digestion of insoluble tissues was used as an assay for the presence of [alpha 1(I)]2alpha 2 and [alpha 1(III)]3 collagens. Both types are present in human skin, intestine, liver, spleen, kidney, lung, aorta, umbilical cord, placental membranes, and myocardium. Bone and tendon contain [alpha 1(I)]2alpha 2 collagen but, unlike the other tissues, lack [alpha 1(III)]3 collagen. Both [alpha 1(I)]2alpha 2 and[alpha 1(III)]3 collagens are present in scars of human skin, myocardium, tendon, and liver and of rabbit skin. The degree of hydroxylation of proline was 4 to 5% lower in the same peptides in skin, bone, and tendon than in the other tissues. The degree of hydroxylation of lysine in the same peptides derived from different tissues varied more widely.     

Corneal glycoconjugates: an ultrastructural lectin--gold study

The oligosaccharide chains of cell surface and extracellular matrix glycoconjugates are essential for the biological properties of these molecules. We have, therefore, investigated carbohydrate residues in the rat cornea using biotinylated lectin--gold probes. Fixed corneas were removed and embedded in Lowicryl HM20 or LR White. Ultrathin sections were incubated in one of the lectins: Triticum vulgare (WGA), Canavalia ensiformis (Con A), Griffonia simplicifolia (GS-1), Limax flavus (LFA) and Allomyrina dichotoma (Allo A), followed by streptavidin--gold, or the sections were incubated in cationic colloidal gold. Semi-quantification of gold labelling was determined for corneal endothelium, Descemet's membrane, stroma and epithelium from electron micrographs. WGA and Con A binding sites were expressed either moderately or strongly through out the cornea, suggesting a preponderance of alpha-mannose and N-acetylglucosamine residues. A particular concentration of these sugars was found in Descemet's membrane. In contrast, GS-1 (specific for alpha-galactose) and Allo A (specific for beta-galactose) labelled all regions weakly. Sialic acid residues, as defined by LFA labelling and the expression of neuraminidase-sensitive cationic colloidal gold binding sites, were sparsely distributed throughout the stroma, Descemet's membrane and endothelium. In contrast, sialoglycoconjugates were found in significant concentrations in the epithelium. Electron microscopy proved useful in providing new information on the cellular and subcellular localization of these lectin binding sites. © Chapman & Hall