Although the proteolytic events accompanying acute and chronic perturbations in striated muscle protein turnover remain to be fully elucidated, the purpose of this paper is to (a) review the chemistry of the nonlysosomal calpain-calpastatin system, and (b) provide evidence for the involvement of a nonlysosomal, calcium-activated neutral protease (calpain) in the response of skeletal muscle protein breakdown to altered nutritional status (diet composition; energy restriction) and increased periods of contractile activity (exercise). In reviewing the literature, it is apparent that calpain is involved in the protein catabolism which accompanies alterations in diet composition and/or energy restriction. The precise mechanism of calpain action remains to be elucidated; however, the role of altered metabolic status contributing to calcium imbalances is discussed relative to increasing protein degradation. Hypotheses for further investigation are provided in regard to identifying the targeting of selected proteins (and organelles) for degradation by calpain.

B16 melanoma was studied in syngeneic C57BL/6J mice as a therapeutic model of melanoma. The irregular behavior of tumor after trochar passage was eliminated by serial intraperitoneal passage, but abundant melanin production was maintained. Mean viability of dispersed suspensions was 56%. Median survival time after injection of lo7 cells intraperitoneally was 11-16 days (average 13.20). I n vivo doubling time was estimated at 3.24 days. Tenfold increase time was approximately 10.75 days. Preliminary studies with rabbit antiserum demonstrated possible enhancement after incubation with tumor in vitro, and a possible therapeutic effect after administration in vivo.