Intracellular pigment cell

Leu-amide) isolated from cockroach heads (16). MRCH/PBAN peptides do not resemble any of the crustacean chromatophorotropins, and the former peptides may not be active on crustacean chromatophores and eye pigment cells. It remains unknown whether MRCH influences rapid color changes brought about by intracellular pigment migration in insects. 

Within cells, proteins, organelles, and other membrane-limited vesicles, organelles, and proteins are frequendy transported distances of many micrometers along well-defined routes In the cytosol and delivered to particular addresses. Diffusion alone cannot account for the rate, directionality, and destinations of such transport processes. Findings from early experiments with fish-scale pigment cells and nerve cells first demonstrated that microtubules function as tracks In the Intracellular transport of various types of cargo. Eventually, two families of motor proteins—kinesins and dyneins— were found to mediate transport along microtubules. 

In photosynthetic eukaryotic cells, both the light-de-pendent and the carbon-assimilation reactions take place in the chloroplasts (Fig. 19-38), membrane-bounded intracellular organelles that are variable in shape and generally a few micrometers in diameter. Like mitochondria, they are surrounded by two membranes, an outer membrane that is permeable to small molecules and ions, and an inner membrane that encloses the internal compartment. This compartment contains many flattened, membrane-surrounded vesicles or sacs, the thylakoids, usually arranged in stacks called grana (Fig. 19-38b). Embedded in the thylakoid membranes (commonly called lamellae) are the photosynthetic pigments and the enzyme complexes that carry out the light reactions and ATP synthesis. The stroma (the aqueous phase enclosed by the inner membrane) contains most of the enzymes required for the carbon-assimilation reactions. 

The basis of phenotypic discrimination of closely related species via Raman spectroscopy lies in its sensitivity to the intracellular molecular components including extrachromosomally encoded phenotypes, such as the Bacillus anthracis or B. thuringiensis toxins or polyglutamic acid capsules. Other prominent examples are cell storage materials like the polyhydroxy butyric acid (PHB), carotenoid-based pigments like sarcinaxanthin, hemoproteins like cytochrome or calcium dipicolinate (CaDPA). Raman spectra of single bacteria, in which the latter four intracellular substances occur, are shown in... 

PEDF, first purified from human retinal pigment epithelial cultures as a factor that induces neuronal differentiation of cultured retinoblastoma cells (Tombran-Tink et al., 1991 Steele et al., 1993), has been recently shown to regulate normal angiogenesis in the eye (Dawson et al., 1999). PEDF is found both intracellularly and extracellularly in the fetal and early adult eye but is lost at the onset of senescence (Becerra, 1997 Araki et al., 1998). It is down-regulated by hypoxia and induced in the retina as a result of... 

Cells have substantial chemical defenses against the UV photoproducts produced in seawater and intracellular fluids. Many organisms have antioxidants (e.g., carotenoids, ascorbate, tocopherols, anthocyanins, and tridentatols) that quench photo-oxidative reactions.64-67 Cells also have enzymes (e.g., catalase and superoxide dismutase) that can counteract the oxidative nature of peroxides and other radicals.26 Some compounds, such as the UV-absorbing pigment melanin, can act as both optical filter and antioxidant.68 The MAA mycosporine-glycine (Figure 15.3) functions in a similar dual capacity.69 The role of UV-mediated reactions in seawater relative to biological effects is an important current area of study. 

Most MAAs are intracellular, although MAAs can be translocated to external surfaces of cells and organisms because MAAs are found in significant concentrations in the extracellular sheath matrix of some cyanobacteria and in coral mucus.134 163 176 Scytonemin is not found intracellularly. It is located extracellularly in association with the glycan sheath but is not a structural component of the sheath layer.194 197 Scytonemin concentrations are not uniform within the sheath layer, and variations are related to the age of the sheath. In Scytonema myochrous, higher concentrations of scytonemin occur near the base of filaments where the sheath is older and thicker, while at newly formed apical cells, the sheath is usually absent or devoid of pigment.198... 

Cells lack the intracellular proliferation of unit-membrane structures that bear the majority of pigments in purple bacteria. 

Kimura H, Ogura Y, Honda Y, et al. Intracellular sustained release with biodegradable polymer microspheres in cultured retinal pigment epithelial cells. Invest Ophthalmol Vis Sci 1993 34 1487. 

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