pH sensitivity of myosin adenosine triphosphatase and subtypes of myofibres in porcine muscle.

Myofibres from pig were classified generally into two types based on their reaction for myosin ATPase. Type I had a strong reaction for acid-stable myosin ATPase and a weak or negative reaction for alkali-stable ATPase; type II had the reciprocal properties. Types SM, SS and MS were defined and considered to represent types intermediate between I and II; they possibly reflect the dynamic situation of transformation of properties. Experimental results showed the sensitivity of the histochemically demonstrated enzyme to small shifts in pH.