Involvement of cathepsin B- and L-like proteinases in silk gland histolysis during metamorphosis of Bombyx mori.Arch Biochem Biophys. 2001 Jun 01; 390(1):28-34.AB
To identify proteinases involved in programmed cell death of the silk glands of Bombyx mori, we measured enzyme activities in silk gland homogenates. Several peptidyl-4-methylcoumaryl-7-amides (MCAs) and bovine hemoglobin were used as substrates in the presence and absence of proteinase inhibitors. The hydrolysis of t-butyloxycarbonyl-Phe-Ser-Arg-MCA (Boc-FSR-MCA), benzyloxy-carbonyl-Phe-Arg-MCA (Z-FR-MCA), and Z-Arg-Arg-MCA (Z-RR-MCA) was optimal at pH 5.5, 5.0, and 5.5, respectively. It was stimulated by the sulfhydryl compounds or EDTA and inhibited by both cysteine proteinase inhibitors and a cathepsin B-specific inhibitor, l-3-trans-(propyl-carbamoyl)oxirane-2-carbonyl)-L-isoleucyl-L-prolin (CA-074). The hemoglobin hydrolysis at the optimum pH 3.5 was inactivated by cysteine proteinase inhibitors, but stimulated slightly by pepstatin. The cleavage of Arg-MCA (R-MCA) and Leu-MCA (L-MCA) at optimum pH of 7.0 was strongly inhibited by an aminopeptidase inhibitor, puromycin, and by sulfhydryl compounds. The Boc-FSR-MCA, Z-FR-MCA, Z-RR-MCA, and hemoglobin hydrolyzing activities increased in the silk glands dramatically after cocoon formation, while the R-MCA and L-MCA cleaving activities declined. The results strongly suggest the involvement of cathepsin B- and cathepsin L-like proteinases in the histolysis of the silk gland during metamorphosis.