Molecular cellular markers

The lipid transfer proteins (LTPs) are proteins which can be divided into two classes, depending on the molecular weight. In in vitro conditions, it was shown that these proteins are able to transfer phospholipids between cellular membranes (Kader, 1997). The role of LTPs in the process of somatic embryogenesis was shown for the first time in the case of carrot embryos (Sterk et al., 1991). It is postulated that LTPs are involved in cutin biosynthesis and that they can be used as a cellular marker for the development of protodermis in somatic embryos (for a review, see Zimmerman, 1993). LTPs were also found in the extracellular proteins secreted by grapevine somatic embryos (Coutos-Thevenot et al., 1993). In Arabidopsis culture, LTPs were also observed outside the meristematic explant cells, which may indicate that LTPs can be used as a cellular marker during the transition from the somatic to the embryogenic state (Fig. 7). 

It seems that promising cellular markers of cell fate changes exist at the ultrastructural and molecular level (Kiyosue et al., 1992 Permell et al., 1992 Schmidt et al., 1997 Yeung, 1995). 

Gasser, R.B. and Hoste, H. (1995) Genetic markers for closely-related parasitic nematodes. Molecular and Cellular Probes 9, 315—320. 

Monti, J.R., Chilton, N.B., Qian, B.-Z. and Gasser, R.B. (1998) PCR-based differentiation of Necator americanus from Ancylostoma duodenale using specific markers in ITS-1 rDNA. Molecular and Cellular Probes 12, 71—78. 

Romstad, A., Gasser, R.B., Polderman, A.M., Nansen, P., Pit, D.S.S. and Chilton, N.B. (1997) Differentiation of Oesophagostomum bifurcum from Necator americanus by PCR using genetic markers in spacer ribosomal DNA. Molecular and Cellular Probes 11, 169—176. 

Fung and colleagues examined the metabolic conversion of organic nitrates in sub-cellular fractions of bovine coronary artery smooth muscle cells [66, 67]. They found NO-generating capacity to be present in membrane fractions and, with the use of marker enzymes, identified plasma membrane as the primary location. The enzyme involved in bioconversion was not glutathione-S-transferase [68] and differed from those that catalyse activation of organic nitrites [69]. Partial purification [70] established that the molecular sizes of the native enzyme and subunits were approximately 200 kDa and 58 kDa respectively, and that enzymic activity depends on the presence of a free thiol group. 

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