The Molecular Physiology of Calcium 
lin would be lethal.) During this past year, we 
continued our studies of the structural features of 
calmodulin required for proper targeting to cell 
membranes and for regulation of ion channel- 
mediated cell behavior. These studies showed 
that a-single amino acid, unchanged in calmodu- 
lins from plant and animal species, is required for 
full ion channel regulatory activity. 
A spin-off from this study was the production of 
new proteins, by using designer (modified) 
genes, that are useful diagnostic reagents for fu- 
ture explorations of the molecular mechanisms 
involved in ion channel regulation. Knowledge 
about how calmodulin affects the activity of ion 
channels will provide insight into the features of 
another class of proteins and regulatory pathways 
modulated by calcium through calmodulin, thus 
complementing the knowledge gained from stud- 
ies of the protein kinase family of calmodulin- 
regulated proteins. 
The fact that protein kinases are modulated by 
ions whose flux is regulated by ion channels, and 
that ion channels can be regulated by protein ki- 
nase-catalyzed phosphorylations, indicates the 
potential of studies focused on selected calmod- 
ulin-regulated proteins for developing a cohesive 
model of the feedback and cross talk that occurs 
in vivo. 
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