Lack of tissue-specificity of calcium-activated neutral proteases from skeletal muscle and lung of rabbit

Comparison of calpains from rabbit, monkey, human and rat

Two isozymes of calpain, mu-calpain and m-calpain, were purified from rabbit, monkey, human and rat tissues to homogeneity and the apparent molecular masses of the large and small subunits of each calpain species were compared directly. While the molecular masses of the small subunits were the same (28 kDa), those of the large subunits were different depending on the calpain type and animal species: Rabbit mu (79 kDa), rabbit m (75 kDa), monkey mu (79 kDa), monkey m (74 kDa), human mu (78 kDa), human m (73 kDa), rat mu (75 kDa), and rat m (74 kDa). Ca2+-sensitivity of monkey mu-calpain was lower than that of rabbit mu-calpain, but m-calpains from rabbit and monkey shared a similar Ca2+-dependency. Immunoreactivities of rabbit, monkey and rat m-calpains towards anti-rabbit m-calpain monoclonal antibodies were different depending on the antibody species, showing the existence of common and different antigenic sites in these three m-calpains. While monkey mu-calpain still showed weak cross-reactivity with anti-rabbit mu-calpain monoclonal antibodies, rat mu-calpain failed to react with any antibody examined, except for the monoclonal 1D10A7 which reacted with mu- and m-calpains from any animal species. Peptides generated by V8 protease digestion were similar between mu-calpains or m-calpains from rabbit and monkey but, again, the reactivity of monkey calpain peptidesto anti-rabbit calpain antibodies was weak, especially to those of mu-calpain.

A low-calcium-requiring calcium-activated neutral proteinase from human placenta

A low-calcium-requiring calcium-activated neutral proteinase (mu CANP) has been purified to homogeneity from human placenta. The purification procedure includes chromatography on DEAE-cellulose, Ultrogel AcA-22 and DEAE-Sephadex in succession. The purified mu CANP is a thiol proteinase and requires calcium for activity. Half-maximal activation occurs at 40 microM calcium. It is a heterodimer with subunits of 74 kDa and 32 kDa. (The placental mCANP has subunits of 70 kDa and 32 kDa.) Mn2+ or Sr2+, in combination with Ca2+, activates the enzyme synergistically. The presence of both mCANP and mu CANP in equal proportion in human placenta is reported for the first time. This will facilitate a comparative study of these two forms of human calcium-activated neutral proteinase, especially their physiological structural and functional interrelationship. Maximal activation of the autolysed mCANP occurs at a calcium concentration much higher than that for mu CANP; and this autolysed mCANP does not cross-react with antiserum against mu CANP, suggesting that the two forms of proteinase are independent species.

Reconstitution of calpain I and calpain II from their subunits: interchangeability of the light subunits

Calpain (Ca2 +-dependent cysteine proteinase) is known to be a heterodimer, composed of one heavy (called 80K) and one light (called 30K) subunit. Calpain I, a low-Ca2 +-requiring form from porcine and human erythrocytes, and calpain II, a high-Ca2 +-requiring form from porcine kidney, were separated into their respective 80K and 30K subunits by high-performance liquid chromatography on a TSK-Gel G3000SW column in 1 M NaSCN. The isolated 80K subunits from porcine calpains I and II showed Ca2 +-dependent proteolysis, though much depressed and requiring higher Ca2 + concentrations compared with the respective parent calpains. The optimal conditions were set for the reconstitution of a heterodimeric molecule from the once denatured and separated 80K and 30K subunits. In such reconstitution, the 30K subunits of calpains I and II were found to be functionally identical and interchangeable; either a homologous or heterologous 30K subunit lowered the Ca2 + requirement of an 80K subunit significantly and enhanced the proteolytic activity. Subunit interchange could also be demonstrated between porcine and human calpains.