Degradation of smooth-muscle myosin by trypsin-like serine proteinases.

Abstract

1. Hydrolysis of the myosins from smooth and from skeletal muscle by a rat trypsin-like serine proteinase and by bovine trypsin at pH 7 is compared. 2. Proteolysis of the heavy chains of both myosins by the rat enzyme proceeds at rates approx. 20 times faster than those obtained with bovine trypsin. Whereas cleavage of skeletal-muscle myosin heavy chain by both enzymes results in the generation of conventional products i.e. heavy meromyosin and light meromyosin, the heavy chain of smooth-muscle myosin is degraded into a fragment of mol. wt. 150000. This is dissimilar from heavy meromyosin and cannot be converted into heavy meromyosin. It is shown that proteolysis of the heavy chain takes place in the head region. 3. The 'regulatory' light chain (20kDa) of smooth-muscle myosin is degraded very rapidly by the rat proteinase. 4. The ability of smooth-muscle myosin to have its ATPase activity activated by actin in the presence of a crude tropomyosin fraction on introduction of Ca2+ is diminished progressively during exposure to the rat proteinase. The rate of loss of the Ca2+-activated actomyosin ATPase activity is very similar to the rate observed for proteolysis of the heavy chain and 3-4 times slower than the rate of removal of the so-called 'regulatory' light chain. 5. The significance of these findings in terms of the functional organization of the smooth muscle myosin molecule is discussed. 6. Since the degraded myosin obtained after exposure to very small amounts of the rat proteinase is no longer able to respond to Ca2+, i.e. the functional activity of the molecule has been removed, the implications of a similar type of proteolysis operating in vivo are considered for myofibrillar protein turnover in general, but particularly with regard to the initiation of myosin degradation, which is known to take place outside the lysosome (i.e. at neutral pH).

Purification and characterization of myofibril-bound serine protease from crucian carp Carassius giberio langsdorfi muscle

“…Although, according to the reports of Kay et al. a certain intracellular serine protease mainly participates in initial degradation of myofibrillar proteins in mouse muscle, 1,2 only a few studies have been reported on intracellular serine protease in fish muscle. According to the previous studies, fish muscle serine proteases are roughly divided into two groups on the basis of the behavior of solubility in muscle homogenate.…”

Purification, Characterization, and cDNA Cloning of a Myofibril-Bound Serine Proteinase from the Skeletal Muscle of Crucian Carp (Carassius auratus)

“…For the nonlysosomal pathway, three protein degradation systems are involved, including the ubiquitin-proteasome system (2), the calpain-µ and -m system (3), and a serine proteinase system (4)(5)(6). Concerning the serine proteinase system, the involvement of a myofibril-bound serine proteinase (MBSP) is noteworthy.…”

Purification and Characterization of a Myofibril-Bound Serine Proteinase From the Skeletal Muscle of Silver Carp

“…2000). Except calpains (Mykles and Skinner 1983), proteinases involved in the nonlysosomal pathway have been characterized as serine proteinases (Kay et al. 1982a,b).…”