Acidic keratins

Epithelial cells contain keratins cytosolic, intermediate-sized filaments. Each acidic keratin (type I) is partnered with a basic keratin (type II) to form extended, intertwined alpha helices. These heterodimers extend longitudinally and laterally in staggered and/ or end-to-end arrays to form cytosolic intermediate filaments. Different keratin types account for the properties of different types of epithelia. A stratified epithelium provides a barrier consisting of multiple layers of cells in which the basal layer expresses K5-K14 but the supra-basal layers express K1-K10. Junctional epithelium has inner and outer basal layers that contain K5-K14. Its supra-basal layers possess K4 and K13, not K1 and K10 and it therefore has no granular layer. Desmosomes permit water and metabolite exchange beneath the granular layer, but they are mostly absent from junctional epithelium which is fluid-permeable like a simple epithelium. The cells of both basal layers of junctional epithelium proliferate and shed their progeny into the base of the sulcus. Junctional epithelium also secretes and activates TGF-pi, which prevents an inflammatory response to masticatory trauma. 

The soft epithelial keratin intermediate filaments comprise approximately 20 different keratin polypeptides. " The polypeptides, numbered 1 through 20, comprise type II (basic) keratins and type I (acidic) keratins (Table 8.2). This family of intermediate filaments is crucial in diagnostic IHC for the identification of carcinomatous differentiation and for identification of specific carcinoma subtypes. 

Twelve keratins with more acidic isoelectric points form type I (acidic) keratins, and eight keratins with more basic isoelectric points compose the type II (basic-neutral) keratins. " The keratins are products of two gene families Most genes for type II keratins are localized on chromosome 12, and the genes for type I keratins are localized on chromosome 17.H2-ii4 g ch... 

Type II (Basic) Keratin Molecular Wt (kD) Typical Distribution in Normal Tissue Type 1 (Acidic) Keratin Molecular Wt (kD)... 

Fig. 10.28. Formation of a cytokeratin filament. The central rod of the keratin monomer is principally a-helical structure. A specific acidic keratin monomer combines with a specific basic keratin monomer to form a heterodimer coil (a coiled coil structure). Two dimers combine in antiparallel fashion to form a tetramer, and the tetramers combine head-to-tail to form pro to filaments. Approximately eight protofilaments combine to form a filament. The filament is thicker than actin filaments (called thin filaments or micro filaments) and thinner than microtubules (thick tubes) and is therefore called an intermediate filament.

Type 1 Acidic keratins Different epithelial cells express different keratins. 

Intermediate filament protein types 1 and 11 are acidic keratin and basic keratin, found in epithelial cells. Vimentin, desmin, glial fibrillary acidic protein, synemin, and peripherin comprise the type 111 intermediate filaments. The type IV intermediate filaments include nestin and syncoilin, which are located in nervous systems and mostly found in neurons. The nuclear intermediate filaments, lamin A, its splice variant lamin C, and lamin B1 and B2 (type V), form a filamentous support inside the inner nuclear membrane [50]. 

Figure 22.21 Storage modulus of membranes synthesized with (a) polyurethane-keratin salt, (b) polyurethane-dialyzed keratin, (c) polyurethane-acid keratin biofibers, and [d] polyurethane-alkaline keratin biofibers. Numbers 11,13,15,17,19, and 21 indicate grafted percentage of keratin solution added (reprinted with permission of Saucedo-Rivalcoba et al., 2011, Springer [81]).

Amino acids, keratin. See Keratin amino acids Amino acids, keratin, reaction prods, with octanoyl chloride. SeeCapryloyl keratin... 

Definition Condensation prod, of caprylic acid chloride and hydrolyzed keratin Uses Antistat, hair conditioner in cosmetics Capryloyl keratin amino acids CAS 68989-21-1 161133-65-9 Synonyms Amino acids, keratin, reaction prods, with octanoyi chioride Capryloyl animal keratin amino acids... 

CAS 68238-35-7 EINECS/ELINCS 269-409-1 Synonyms Amino acids, keratin Animal keratin amino acids... 

In contrast to the neutral polysaccharides, the carbohydrate skeleton of heparin and mucopolysaccharides is based on an amino sugar uronic acid repeating unit. An important biological difference is that the neutral polysaccharides (glycogen, starch) are metabolic stores, the typical mucopolysaccharides (chondroitin sulfuric acids, keratin sulfate) are important structural materials of connective tissue, and the naturally occurring heparins and heparinoids are trace substances and appear to be associated with special cells. 

Staining Applications Brain spinal cord sperm head tissue culture cytoplasmic vacuoles nucleic acids keratin fibers ... 

The GAGs contain specific sugars such as glucosamine sulfate, N-acetylglucosamine and glucosamine hydrochloride, all very able of attracting water. They form long chains of molecules that retain water, such as hyaluronic acid, keratin sulfate, heparin, dermatin, and chondroitin. 

The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

Amino acid CoUagen Elastin Keratin Albumin... 

Albumen has the largest number of acid and basic groups. It is the most soluble of the proteins present in a hide. The albumen is not a fibrous material, however, and therefore has no value in the leather. Keratin is the protein of the hair and the outermost surface of the hide. Unless the hair is desired for the final product it is removed by chemical and/or physical means. The elastin has Htde acid- or base-binding capacity and is the least soluble of the proteins present. The lack of reactivity of the elastin is a detriment for most leather manufacture. The presence of elastin in the leather greatly limits the softness of the leather. 

The differences in the amino acid chemistry of the hide coUagen and the hair keratin are the basis of the lime-sulfide unhairing system. Hair contains the amino acid cystine. This sulfur-containing amino acid cross-links the polypeptide chains of mature hair proteins. In modem production of bovine leathers the quantity of sulfide, as Na2S or NaSH, is normally 2—4% based on the weight of the hides. The lime is essentially an unhmited supply of alkah buffered to pH 12—12.5. The sulfide breaks the polypeptide S—S cross-links by reduction. Unhairing without sulfide may take several days or weeks. The keratin can be easily hydrolyzed once there is a breakdown in the hair fiber stmcture and the hair can be removed mechanically. The coUagen hydrolysis is not affected by the presence of the sulfides (1—4,7). 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

FIGURE 6.14 (a) Both type I and type II o -keratin molecules have sequences consisting of long, central rod domains with terminal cap domains. The numbers of amino acid residues in each domain are indicated. Asterisks denote domains of variable length. 

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