THE ENZYMOLOGY OF PHOSPHORYLASE-PHOSPHATASE (PROTEIN PHOSPHATASE-1) -A PERSONAL PERSPECTIVE

In this paper we review studies of phosphorylase phosphatase (protein phosphatase-1) that have been the focus of our work for the past two d ecades. The enzymology of the enzyme is complex, and the description o f its properties has taken a great deal of effort. Key discoveries in this process were the isolation of the catalytic subunit of the enzyme , and the discovery of inhibitory proteins, one of which (inhibitor-2) forms a complex with the catalytic subunit. Later it was discovered t hat a number of holoenzyme forms existed, and that these consisted of complexes of the catalytic subunit with different regulatory subunits. In recent years, the cloning of the cDNAs for the catalytic subunit h as demonstrated that it is a Very highly conserved protein and that it plays a critical role in mitosis. Expression of the catalytic subunit in E. coli has opened the way for structure-function studies. The reg ion involved in the binding of toxins which inhibit the enzyme have be en identified by mutagenesis.