Biophysical Studies of Eukaryotic Gene Regulation and Molecular Recognition 
structure of the enzyme complexed with its slow- 
binding inhibitor bestatin, which is a dipeptide 
analogue that lacks a scissile peptide bond. A de- 
tailed analysis of the interactions between besta- 
tin and the active-site residues allowed us to sug- 
gest a mechanism of slow-binding inhibition 
of LAP and other bimetallic, amino-terminal 
exoproteases. 
Finally, the three-dimensional structure of LAP 
also provides some insights into the role that 
post-translational modification plays in the problem 
of recombination. LAP is homologous to pep A, a 
manganese-dependent, hexameric aminopeptidase 
found in Escherichia coli that is required for plas- 
mid ColEl site-specific recombination. 
We will continue similar work with other en- 
zyme systems of biological and biochemical 
importance. 
A computer graphics representation of the three-dimensional structure of the hexameric, zinc- 
dependent leucine aminopeptidase from bovine lens that has been determined to 2.25 A resolu- 
tion. This enzyme is responsible for post-translational modification of proteins and oligopeptides 
and for degradation of aging proteins in a diverse group of organisms ranging from Escherichia 
coli to humans. 
Research of Stephen K. Burley. 
68 
