Conversion of lipotropic peptides by purified cathepsin D of human pituitary: release of gamma-endorphin by cleavage of the Leu(77)-PHE(78) bond.
Cathepsin D (EC 3.4.3.23) purified from human putuitary by affinity chromatography on pepstatin-Sepharose cleaved human beta-endorphin (LPH 61-91) at the Leu(77)-Phe(78) bond after incubation at pH 3.2 for 1-3. Incubation with smaller lipotropic fragments (enkephalin, alpha-endorphin, gamma-endorphin) did not lead to further degradation. Cleavage sites were identified following the separation of danyslated or iodinated peptides on polyamide sheets accompanied by N-group determination, or following slab-gel electrophoresis of the iodinated peptides. Cleavage at the above site was blocked using an analog containing D-Leu(77). Breakdown of porcine beta-lipotropin (LPH 1-91) was slower and required an 18 h incubation. A product LPH 1-77 was tentatively identified based in part on its mobility on slab gels as compared to beta-LPH and beta-endophine and by N-group determination of cleavage products.
Benuck
M
M
Institute for Neurochemistry, Rockland Research Institute, Wards Island, N.Y. 10035, USA.
Grynbaum
A
A
Cooper
T B
TB
Marks
N
N