SS Linkages Research Articles

Thiolated sodium alginate conjugates for mucoadhesive and controlled release behavior of metformin microspheres

The absorption of BCS III drugs can be improved by inhibiting the P-glycoprotein (P-gp) efflux and by increasing the mucoadhesion of natural polymers. In the present study, an esterification of sodium alginate (SA) with thioglycolic acid (TGA) was applied for the preparation of thiolated sodium alginate (TSA). The Ellman's test was applied to quantify the thiol group and a di-sulphide bond test was performed to confirm any SS linkages. The FTIR, DSC, XRD, 1H NMR and charring point determinations were confirmed the thiol group of TSA. The gel like rheological properties with porcine mucous was confirmed by viscoelasticity properties and the mucoadhesion with the rabbit intestine was carried out after compression of 30 mg tablets of TSA. The content of thiol group was in the range of 320–730 μmoL/g of the polymer. The FTIR spectrum showed a characteristic peak of sulfhydryl group at 2557 cm−1 in TSA and the reduction of the charring point from 220 °C to 178 °C was confirmed the thiolation of TSA. A direct relationship of mucoadhesion and swelling was observed with the concentration of TGA and SA, respectively. The prepared microspheres were 2–7 μm in size, excellent rheological properties and non-fickian drug release behavior was observed.

Differences in physicochemical, morphological, and structural properties between rice starch and rice flour modified by dry heat treatment

The differential influence of dry heat treatment on pasting, thermal, morphological, and crystalline structural properties of glutinous rice starch (GRS) and glutinous rice flour (GRF) in a dry state for 0, 2, or 4 h at 130°C were studied. The results revealed that the viscosity and thermal stability of GRS and GRF increased after dry heat treatment. Peak viscosity of GRF rose nearly threefold from 1156 to 3145 cP. The number of disulphide bonds in GRF increased from 1.93 to 3.19 μmol/g, indicating the covalent SS linkages after dry heat treatment may result in the changes of protein structure, which may greatly influence properties of dry heated flour. Morphology of gelatinized GRS was denser, and a strong laminar structure was observed for gelatinized GRF after dry heat treatment. Fourier transformation infrared spectroscopy indicated that both GRS and GRF had relatively higher transmittance intensities in the region of 1068 and 1022 cm−1. X‐ray diffraction showed that the crystallinity of GRS increased from 32.82 to 35.02% and GRF increased from 29.32 to 34.14% after dry heat treatment. Dry heat treatment had greater effects on viscosity and structural properties of GRF than those of GRS.

An amphiphilic selenide catalyst behaves like a hybrid mimic of protein disulfide isomerase and glutathione peroxidase 7.

Protein disulfide isomerase (PDI) and glutathione peroxidase 7 (GPx7) cooperatively promote the oxidative folding of disulfide (SS)-containing proteins in endoplasmic reticulum by recognizing the nascent proteins to convert them into the native folds by means of SS formation and SS isomerization and by catalyzing reoxidation of reduced PDI with H2O2, respectively. In this study, new amphiphilic selenides with a long-chain alkyl group were designed as hybrid mimics of PDI and GPx7 and were applied to the refolding of reduced hen egg-white lysozyme (HEL-R). Competitive SS formation at pH 4 using HEL-R and glutathione (GSH) in the presence of the selenide catalyst and H2O2 showed that the amphiphilic selenides can preferentially catalyze SS formation of HEL-R, probably on account of hydrophobic interactions between the protein and the catalyst. In contrast, simple water-soluble selenides did not exhibit such behavior. In addition, when the pH of the solution was adjusted to 8.5 after the SS formation, surviving GSH promoted the SS isomerization of misfolded HEL to recover the native SS linkages. Thus, the amphiphilic selenides designed here could mimic the function of the PDI-GPx7 system. The combination of a water-soluble selenide and a long-chain alkyl group would be a useful motif in designing medicines for both protein misfolding diseases and antioxidant therapy.

Reinvestigation of the Oxidative Folding Pathways of Hen Egg White Lysozyme: Switching of the Major Pathways by Temperature Control

It has been well established that in the oxidative folding of hen egg white lysozyme (HEL), which has four SS linkages in the native state (N), three des intermediates, i.e., des[76–94], des[64–80], and des [6–127], are populated at 20 °C and N is dominantly formed by the oxidation of des[64–80] and des[6–127]. To elucidate the temperature effects, the oxidative folding pathways of HEL were reinvestigated at 5–45 °C in the presence of 2 M urea at pH 8.0 by using a selenoxide reagent, DHSox. When reduced HEL was reacted with 1–4 equivalents of DHSox, 1S, 2S, 3S, and 4S intermediate ensembles with 1–4 SS linkages, respectively, were produced within 1 min. After the oxidation, 3S was slowly converted to the des intermediates with formation of the native structures through SS rearrangement. At 5 °C, des[76–94] was populated in the largest amount, but the oxidation to N was slower than that of des[64–80] and des[6–127]. At 35 °C, on the other hand, des[64–80] and des[6–127] were no longer stable, and only des[76–94] was populated. The results suggested that the major folding pathways of HEL can be switched from one to the other by temperature control.

Kinetic and thermodynamic analysis of the conformational folding process of SS-reduced bovine pancreatic ribonuclease A using a selenoxide reagent with high oxidizing ability

Redox-coupled folding pathways of bovine pancreatic ribonuclease A (RNase A) with four intramolecular disulfide (SS) bonds comprise three phases: (I) SS formation to generate partially oxidized intermediate ensembles with no rigid folded structure; (II) SS rearrangement from the three SS intermediate ensemble (3S) to the des intermediates having three native SS linkages; (III) final oxidation of the last native SS linkage to generate native RNase A. We previously demonstrated that DHSox, a water-soluble selenoxide reagent for rapid and quantitative SS formation, allows clear separation of the three folding phases. In this study, the main conformational folding phase (phase II) has been extensively analyzed at pH 8.0 under a wide range of temperatures (5–45°C), and thermodynamic and kinetic parameters for the four des intermediates were determined. The free-energy differences (ΔG) as a function of temperature suggested that the each SS linkage has different thermodynamic and kinetic roles in stability of the native structure. On the other hand, comparison of the rate constants and the activation energies for 3S→des with those reported for the conformational folding of SS-intact RNase A suggested that unfolded des species (desU) having three native SS linkages but not yet being folded are involved in very small amounts (<1%) in the 3S intermediate ensemble and the desU species would gain the native-like structures via X-Pro isomerization like SS-intact RNase A. It was revealed that DHSox is useful for kinetic and thermodynamic analysis of the conformational folding process on the oxidative folding pathways of SS-reduced proteins.

Characterization of Kinetic and Thermodynamic Phases in the Prefolding Process of Bovine Pancreatic Ribonuclease A Coupled with Fast SS Formation and SS Reshuffling

In the redox-coupled oxidative folding of a protein having several SS bonds, two folding phases are usually observed, corresponding to SS formation (oxidation) with generation of weakly stabilized heterogeneous structures (a chain-entropy losing phase) and the subsequent intramolecular SS rearrangement to search for the native SS linkages (a conformational folding phase). By taking advantage of DHS(ox) as a highly strong and selective oxidant, the former SS formation phase was investigated in detail in the oxidative folding of RNase A. The folding intermediates obtained at 25 °C and pH 4.0 within 1 min (1S°-4S°) showed different profiles in the HPLC chromatograms from those of the intermediates obtained at pH 7.0 and 10.0 (1S-4S). However, upon prolonged incubation at pH 4.0 the profiles of 1S°-3S° transformed slowly to those similar to 1S-3S intermediate ensembles via intramolecular SS reshuffling, accompanying significant changes in the UV and fluorescence spectra but not in the CD spectrum. Similar conversion of the intermediates was observed by pH jump from 4.0 to 8.0, while the opposite conversion from 1S-4S was observed by addition of guanidine hydrochloride to the folding solution at pH 8.0. The results demonstrated that the preconformational folding phase coupled with SS formation can be divided into two distinct subphases, a kinetic (or stochastic) SS formation phase and a thermodynamic SS reshuffling phase. The transition from kinetically formed to thermodynamically stabilized SS intermediates would be induced by hydrophobic nucleation as well as generation of the native interactions.

Counting Sulfhydryls and Disulfide Bonds in Peptides and Proteins Using Mercurial Ions as an MS-Tag

Organic mercurial compounds are the most specific and sensitive reagents for reaction with the sulfhydryl groups (SHs) in peptides and proteins because of the strong mercury-sulfur affinity. Using the monofunctional organic mercury ion RHg(+) as a mass spectrometry (MS)-tag has the advantages of reacting with one sulfhydryl group, offering definite mass shift, and especially stable and characteristic nonradioactive isotopic distribution. Mass spectrometric analysis of derivatized sulfhydryls in peptides/proteins is thus an alternative for precisely counting the number of sulfhydryl groups and disulfide bonds (SS). Here the tags used include monomethylmercury chloride, monoethylmercury chloride, and 4-(hydroxymercuri) benzoic acid. The feasibility of this strategy is demonstrated using HPLC/ESI-MS to count SHs and SS in model peptides/proteins, i.e., glutathione, phytochelatins, lysozyme and beta-lactoglobulin, which contain increasing SHs and various SS linkages.

Direct Observation of Conformational Folding Coupled with Disulphide Rearrangement by Using a Water-soluble Selenoxide Reagent—A Case of Oxidative Regeneration of Ribonuclease A under Weakly Basic Conditions

Oxidative regeneration pathways of bovine pancreatic ribonuclease A (RNase A), which has four SS linkages, were studied at 25 degrees C and pH 8.0 by using trans-3,4-dihydroxy-1-selenolane oxide (DHS(ox)), a new selenoxide reagent with strong oxidation power. The short-term folding study using a quench-flow instrument ( approximately 1 min) revealed that early intermediates (1S, 2S, 3S and 4S) are formed stochastically and irreversibly from the reduced protein (R) and do not have any stable structures. In the long-term folding study ( approximately 300 min), on the other hand, slow generation of the key intermediates (des[65-72] and des[40-95]) through SS rearrangement from the 3S intermediate ensemble was observed, followed by slight formation of native RNase A (N). The parallel UV and CD measurements demonstrated that formation of the key intermediates is accompanied with the formation of the native-like structures. Thus, DHS(ox) allowed facile identification of the conformational folding steps coupled with SS rearrangement on the major oxidative folding pathways.

Common Molecular Features among Amaranth Storage Proteins

The structure of albumin 2 protein fraction of amaranth was investigated. It was formed by several major polypeptide subunits of molecular masses of 52.3 ± 0.8, 54 ± 2, and 56 ± 1 kDa. The former and the latter subunits were composed of a peptide of molecular mass between 31 and 38 kDa linked by S−S bonds with another peptide of molecular mass between 19 and 23 kDa. The 54 kDa subunit together with the 31−38 and 19−23 kDa subunits formed S−S-linked aggregated polypeptides. Lyophilized albumin 2 was highly polymerized, having a complex monomer component with a molecular mass of 300 ± 10 kDa. The polymers were partially stabilized by SS linkages. Because of these structural characteristics, albumin 2 was very similar to amarantin except for the presence of the 54 kDa subunit and its tendency to polymerize. Two components were obtained by gel filtration of globulin fraction. The major one exhibited heterogeneity of species and showed some common features with albumin 2. The minor component eluted at a lower volume and also showed heterogeneity, with a main species of 7S and a minor one of 12S. Their major peptides had molecular masses of 78, 72, 39, 30, and 20 kDa similar to the 7S type globulin. Its size, larger than that of amarantin, is different from a 7S type globulin, but the possibility of becoming polymerized or having a shape quite different from that of a sphere cannot be dismissed. Keywords: Amaranth; globulin; albumin 2; protein structure; gel filtration; electrophoresis

Type and location of SS linkages in human hair and their relation to fiber properties in water

The changes in the mechanical properties accompanying the reduction of disulfide (SS) linkages in hair were studied. A variety of extents of thiol groups were introduced into hair by treatments with thioglycolic acid and tri-n-butyl phosphine. The reduced fibers swollen with an aqueous 11M LiBr solution containing N-ethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8M LiBr and diethylene glycol mono-n-butyl ether. The crosslink density was determined from the shear modulus of the swollen fiber. It was found that the SS linkages can be divided into two groups : the intermolecular linkages group (SS 1 and SS 2 ) and the intramolecular linkages group (SS 3 ). The effect of the SS bond scission on the shear modulus of the reduced fibers in water was also studied. It was further found that intermolecular SS 1 linkages do not respond to the shear modulus of fiber in water, and the amounts of SS 1 , SS 2 , and SS 3 are about 35, 18, and 47% of the total cystine content in hair (623 μmol/g), respectively. With respect to the location of SS linkages in hair, important suggestions were obtained : the intermolecular SS 1 and SS 2 linkages are located in the microfibril and the matrix, and the former are more accessible to water than the latter ; and SS 3 linkages are localized within the hydrophobic region of the matrix.

Type and location of SS linkages in human hair and their relation to fiber properties in water

Type and location of SS linkages in human hair and their relation to fiber properties in water

口腔再建皮弁の組織学的研究

Various cutaneous flaps have been used to reconstruct intraoral defects created by tumor resection. Transplanted cutaneous flaps clinically show changes such as color changes and scaling. To better understand the biological conditions of reconstructed flaps that survive in the intraoral environment, patients in whom various periods had passed since reconstruction operations were clinically observed, and biopsy specimens taken from their flaps were examined histologically, histochemically and immunohistochemically.Seventeen major flaps, including delto-pectoral flaps, pectoral major myocutaneous flaps and forearm flaps, were used to reconstruct intraoral defects remaining after the resection of oral cancer. Irradiated flaps were excluded. Biopsy specimens were taken from both the mid-portion of each flap and the junction between the flap and the surrounding oral mucosa. Histological, histochemical and immunohistochemical examinations were performed as follows. A formalin-fixed specimen was dehydrated and embedded in paraffin. Hematoxylineosin, periodic acid-Schiff with and without diastase digestion, and alcian-blue were used to stain the deparaffinized sections of the specimens. The deparaffinized sections also underwent N-(7-dimethylamine-4-methl-3-coumarinyl) maleimide (DACM) staining to examine the distribution patterns of SH groups and SS linkages of cellular proteins in the epidermis. Immunohistochemically, frozen sections were first cut in a cryostat and stained with monoclonal antibodies. Anti-hair keratin monoclonal antibodies (HKN-2, 4, 5, 6, 7), anti-basal cell epithelioma keratin monoclonal antibodies (BKN-1), K92, and RKSE60 were used.The clinical features of cutaneous flaps seemed to depend on their location in the oral cavity rather than the period since operation or the kind of flap. Although the horny layer of the epidermis of the flaps showed thinning histologically, the epidermis showed a normal pattern of SH to SS conversion by DACM staining histochemically, as well as normal keratin expression by keratin staining immunohistochemically. The tongue epithelium adjacent to the flaps often showed flattening. Some specific keratins of the tongue epithelium were still recognized but hard keratin was not. Although cutaneous flaps may be influenced by environmental factors in the oral cavity, the flap tissues seem to retain their original cell differentiation.

Increased SS bonds in chronic solar elastosis: a study with N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain

We have studied the distribution of SH groups and SS linkages in solar elastosis, in comparison with that in aged and juvenile sun-unexposed skin, using N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain. In heavy solar elastosis we found increased fluorescence for SS bonds in the upper and middle reticular dermis in the elastotic masses; these were separated from the epidermis by a network of actinically-damaged, SS-positive elastic fibers, showing irregularly and variously interwoven oxytalan and elaunic fibers. These latter, unlike the elastotic masses, revealed also SH groups. In moderate and weak elastosis, where the thick irregular masses were absent, the fluorescence for SH and SS linkages was present in equal proportions in the altered elastic fibers; collagen bundles revealed only fluorescence for SS bonds. Aged and juvenile sun-unexposed skin showed the same proportions of SH and SS linkages in the changed elastic fibers. Collagen bundles of aged and juvenile skin showed fluorescence for SS bonds; SH groups were present on a few collagen fibers only in aged skin. Our results are consistent with opinion supporting an elastic origin of elastotic degeneration, which could be the consequence of a defect, due to chronic solar exposure, in one of the steps — degradation or synthesis — of metabolic turnover of elastic fibers, resulting in abnormal and excessive polypeptide chains extremely rich in disulfide bonds.

Cross‐linking structure of keratin. IV. The number of cross‐linkages in low‐sulfur components and the volume fraction of high‐sulfur domains in various α‐keratin fibers

AbstractVarious α‐keratin fibers that had been treated with an 11M LiBr solution containing N‐ethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8M LiBr and diethylene glycol mono‐n‐butyl ether. Stress—strain relations of the swollen fibers were treated with a two‐phase model: a mechanically stable phase of higher cross‐linked domains and a rubber phase with lower cross‐link density. Stress—strain curves for a variety of keratins (three different human hairs, six different wools, mohair, cashmere, llama, alpaca, angora, and opossum) were analyzed by applying non‐Gaussian chain statistics to the swollen keratin network, including microdomains, which act as reinforcing filler particles in rubber. The phase structures of unswollen domains and swollen rubber were considered to originate from different structural components characteristic of α‐keratin, namely, the high‐sulfur matrix and the low‐sulfur microfibrils being randomized by swelling. It has been suggested that (1) the modulus of swollen fibers increases with increase of the content of disulfide (SS) in keratins, (2) the volume fraction of high‐sulfur domains increases with increase of SS content, and (3) the number of intermolecular cross‐links in the rubber region of low‐sulfur proteins is virtually the same among keratins and reaches about 65–75% of the SS linkages in the corresponding proteins. Some discussion has been made on the SS bonding in situ, namely, SS linkages between the low‐sulfur proteins, between the low‐sulfur and the high‐sulfur proteins, and between the high‐sulfur proteins in keratins. © 1993 John Wiley &amp; Sons, Inc.

Histochemical observation of the cell membrane complex of hair.

The present work is to clarify the fine structure of hair fiber components, especially Cell Membrane Complex (CMC) of cuticle. Hair fibers were treated with either hydrophilic N-acetylcysteine (NAC), thioglycolic acid (TGA) or hydrophobic tri-n-butyl-phosphine (TBP) for disulfide bond (SS) reduction. It was confirmed that the sulfhydryl residues (R-SH) were mainly produced in the CMC region by the initial reduction, being observed fluorescent from R-SH after labelled with N-(7-dimethylamino-4-coumarinyl)-maleimide (DACM). These reduced fibers were grafted with methyl methacrylate (MMA) by using lithium bromide and potassium persulfate system. The location of the grafted polymer in the fiber was determined as a low electron density region by a high resolution transmission electron microscopy. The grafted polymer was mainly observed in the CMC and the endocuticle of the TGA-reduced fiber, but not in that of the TBP-reduced fiber. Especially a homogeneous unstained layer was found in the middle region of the δ-layer of cuticle CMC of TGA-reduced hair. When hairs were prefixed with ruthenium tetroxide instead of osmium tetroxide, a structural change of the δ-layer to lamella-like structure were observed in the CMC of cuticle without graft copolymerization. These results suggest that the CMC consists of not only relatively hydrophilic regions containing SS linkages which the reduction brings about a large space for polymer uptake but hydrophobic lamella-like lipid layers.

Morphogenesis of the cornoid lamella: histochemical, immunohistochemical, and ultrastructural study of porokeratosis

To elucidate the morphogenesis of cornoid lamellae (CL) in porokeratosis, skin lesions of three cases of disseminated superficial actinic porokeratosis and a case of linear porokeratosis were examined. By N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide staining, SH groups were present in the living layer of the epidermis beneath CL and irregularly disappeared at the bottom of CL, whereas SS linkages appeared in dyskeratotic cells in the living layer and in the irregularly shaped cell membranes of the horny cells. Epidermis beneath CL showed an increased and irregular involucrin expression. Ultrastructurally, the living keratinocytes contained many cytoplasmic vacuoles and had a smaller number of lamellar bodies than normal. Intercellular lamellar sheets were incompletely formed. The dyskeratotic cells and the lower horny cells contained many small vacuoles but formed a marginal band. The horny cells of CL also formed a marginal band and, further, a keratin pattern. CL may be formed by hyperproliferative atypical kertatinocytes which keratinize rapidly and irregularly and show defective desquamation due to the paucity of intercellular lamellar sheets.

アスコルビン酸およびその関連物質のホームベーカリーの使用による製パン効果の検討

L-Ascorbic acid (AsA) and its related compounds were tested for the improver of Breadmaking by Homebakery. AsA and dehydro-L-ascorbic acid (DHA) showed almost similar effects on the improvement of specific volume of the bread by adding around 8 ppm to wheat flour. But, 2, 3-diketo- L-gulonic acid (DKG) had no appreciable effect on the specific volume of the bread with the concentration up to 50 ppm. When the mixing time of the breadmaking was changed from 25 min to 85 min by 10-min intervals, the specific volume of the bread baked by 4-hr course was quite different from that of 25-min mixing : AsA gave no distinct decrease in the specific volume ; however, in the case of DKG and the control, the specific volume decreased with the increase of the mixing time. When the breadmaking time was extended from 4 hr to 8 hr, the specific volumes of the bread baked by the addition of AsA were distinctly decreased with the increase of the amount of AsAadded, but DHA showed no distinct effect on the increase of the loaf volume of bread baked. The SH concentrations in dough increased 4-fold after the addition of dry yeast, compared with the dough just before the addition of the yeast. This may suggest that the SH compounds in the yeast affect the cross-linking by SS linkages in the dough. For the breadmaking with an automatic breadmaking apparatus, some interactions between AsA, its related compounds and SH groups in the dough and yeast must be important for the breadmaking.

SH Abundant Body in Infantile Digital Fibromatosis

A case of infantile digital fibromatosis was studied with regard to the distribution of -SH groups and SS linkages, using N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain. Tumor cells showed a strong fluorescence in the cytoplasm from the -SH stain. A brilliant -SH fluorescence was also homogenously present on the intracytoplasmic inclusions. SS reactivity was negative. Although further studies should be necessary to ascertain this finding, the DACM stain may make a simple and objective diagnostic method of infantile digital fibromatosis.

Intraepidermal pilar epithelioma: A new dermatopathologic interpretation of a skin tumor

An intraepidermally developed epithelial cell tumor, forming multiple nests, was examined to identify its cytologic characteristics. Histochemically, the tumor cells contained neither glycogen nor lipid substance. By N-(7-dimethylamino-3-methyl-4-coumarinyl)maleimide staining, the cytoplasm of the tumor cells in the periphery of each nest was rich in SH groups but not in SS linkages, whereas centrally located homogeneous tumor cells contained SS diffusely but no SH. The tumor cells showed no activity of phosphorylase and a weak activity of succinic dehydrogenase. Immunohistochemically, antihair keratin monoclonal antibodies specific for hair cells decorated the tumor cells, but carcinoembryonic antigen staining showed no positivity. Ultrastructurally, the tumor cells underwent a keratinization forming a fingerprint pattern of keratin filaments; however, membrane-coating granules and marginal bands were not formed. These intraepidermal tumor cells may have cytologic natures similar to those of hair cortical cells. The term intraepidermal pilar epithelioma is proposed as a diagnosis for this tumor.

The -SH and SS positive components in dermal connective tissues: a study by N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain.

Although -SH and SS positive components in dermal connective tissue have been observed by N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM) stain, their nature is as yet unknown. In our study, we stained several organs such as human skin, rabbit aorta, auricle, and trachea using DACM stain, and studied the distribution of -SH groups and SS linkages among the elastic fibers in those organs. In the dermis of human skin, a moderately strong fluorescence by both -SH and SS stain was present all over the layer, especially in the lower half among collagen fibers in a fine linear or wavy pattern, and a fluorescence ascending vertically from the lower papillary dermis toward the epidermis was also observed. In rabbit aorta, a strong fluorescence by both -SH and SS stain was observed on well-developed elastic fibers. In the matrix of rabbit elastic cartilage, a strong reticular fluorescence by both -SH and SS stain was present. On the other hand, in rabbit hyaline cartilage, no -SH fluorescence was present on any components of the cartilage. However, though a diffuse moderate fluorescence for SS linkages was observed in the matrix, there was no reticular fluorescence such as that seen in the elastic cartilage. These results suggest that the -SH and SS components observed in the dermis by DACM stain are in fact elastic fibers, more precisely, "elastic tissue microfibrils".