Serine-threonine system

These principles are nicely illustrated by the contrast between the serine-threonine and serine-allothreonine (allothr) systems. The relative orientation of molecular serine vis-a-vis its various crystal faces suggests that allothr can be adsorbed on the homotopic 100 faces as well as on the enantiotopic 011 faces (Figure 21). 

A lot of biologic membrane systems and cellular organelles contain kinases, which transfer phosphate groups to proteins, especially to serine, threonine, and tyrosine residues. Self-phosphorylation of enzymes leading to acylphosphates or phosphoamides can be observed, too. With respect to their chemical stability, these phos-phoproteins are classified into acid-stable (alkali labile), hydroxyl-amine-sensitive, and acid labile. 

We and others have demonstrated that Raf-1 protein serine/threonine kinase is a druggable signaling molecule in cancer therapy (1,13,17,21-25). Our laboratory has developed a novel cationic liposomal formulation for systemic delivery of intact raf ASO (LErafAON) to normal and tumor tissues in mice (13,17). The liposome-entrapped raf antisense oligonucleotide (LErafAON) is also the first liposomal ASO drug tested in humans (26,27). Systemically delivered cationic liposomal nanoparticles containing rafsiRNA (LErafsiRNA) also inhibit Raf-1 protein expression in tumor and most normal tissues in human prostate tumor (PC-3)-bearing athymic mice (Fig. 1 and Color Plate 1, see Color Plate Section). 

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