Programmed cell death—V. Cytolytic enzymes in relation to the breakdown of the intersegmental muscles of silkmoths

Abstract

During the 3 week period of adult development cytolytic enzymes are synthesized and sequestered in lysosome-like particles in the intersegmental muscles of the silkmoth abdomen. A cathepsin begins to increase in titre during the first few days of adult development and continues to increase slowly during the first 2 weeks of this period. Then, during the final week of adult development, it increases at a logarithmic rate of about 30 per cent per day. In centrifuged homogenates prepared in sucrose, most of the enzymatic activity accompanies the mitochondrial ‘fraction’, from which a substantial proportion can be relased by osmotic shock or by detergents. In sucrose homogenates of degenerating muscle, a lesser fraction of the enzyme is sedimentable, and a greater percentage of the total enzymatic activity is ‘free’ prior to the addition of detergent. An acid phosphatase follows a similar pattern but is more readily solubilized by the homogenization procedure. These enzymes are considered to be directly responsible for the destruction of the intersegmental muscles.