Tertiary structure in deletion analogs of human .beta.-endorphin: resistance to leucine aminopeptidase action

Abstract

The presence of tertiary structure in aqueous solutions of the amino-terminal nine- and seventeen-residue analogues of human .beta.-endorphin has been further demonstrated by leucine aminopeptidase (LAP) cleavage of the amino-terminal tyrosine. The reactions were followed by difference absorption spectroscopy. While the amino-terminal pentapeptide showed no resistance to LAP action, the nonapeptide displayed definite resistance. The heptadecapeptide analogue was found to be completely refractory to LAP action under the conditions employed. Thermolysin cleavage of the Phe4-Met5 bond in the longer analogues destroys the tertiary structure, not only removing the previously reported red shift in tyrosine absorption but also resulting in complete normalization to LAP digestion.