| Popis: |
When the transport properties of mCAT-1 were described in 1991, the y+ carrier and major transporter for cationic amino acids seemed to be discovered. Today, we know that there are at least three different CAT isoforms that mediate y+ activity and the family might be growing. In addition, transport systems for cationic amino acids other than y + have been described and proteins that induce the respective transport activities have been identified. Consequently, the transport of cationic amino acids appears to be a complex process involving many proteins— carriers and possibly also regulatory proteins—whose expression is cell-specific and dependent on a variety of external stimuli. The multitude of different carrier proteins possibly offers an opportunity to inhibit specifically transport processes in a given cell without interfering with the overall transport of cationic amino acids. A functional knockout of individual proteins would lead to a better understanding of the physiological role of each protein. To date no specific inhibitors are available to block the function of the CAT proteins or other transporters for cationic amino acids. The discovery of such inhibitors not only could provide scientific tools, but could also lead to the development of new drugs targeting specific carrier proteins. It would, for instance, be desirable to inhibit CAT-2B in cells expressing the inducible NOS without interfering with CAT-1 activity. If CAT-2B played a crucial role in delivering substrate to NOS II, NO production could be reduced without interfering with other processes depending on cationic amino acids supply by CAT- 1. |
