REACTIVITY OF MUSCLE TRANSGLUTAMINASE ON CARP MYOFIBRILS AND MYOSIN-B

(1) Carp ordinary muscle contained TGase activity of 1.5 unit per g of wet weight which was easily extractable with a solution at low ionic strength. The TGase, partially purified by DEAE-cellulose and gel filtration chromatographies, showed molecular weight of about 80,000 and Ca2+-requirement for full activation. These properties characterize the enzyme as a "tissue" TGase. (2) It was observed that rate and extent of TGase-catalyzed incorporation of MDC into myosin B and myofibrils were lower than those into acetylated casein. (3) The reactivity of TGase on carp myosin B and myofibrils was fluctuated by the conformational alteration of the substrate proteins; the extent of MDC incorporation appeared to be 2.4-fold elevated in "soluble myosin B" than "insoluble myosin B" or myofibrils at identical amount of the enzyme. (4) MDC was preferentially labeled on myosin heavy chain, actin, and troponin-T among the constituent proteins of myofibrils.