A species of neutral protease having high affinity for Ca2+ in the 10(-5) M range, originally found in canine cardiac muscle (Mellgren, R.L. (1980) FEBS Lett. 109, 129-133), is detected in a wide variety of rat tissues when a sensitive assay with 125I-iodinated casein as substrate is employed. This species of protease absolutely requires Ca2+, and other divalent cations are practically inactive. Although the activity of this enzyme apparently shows striking diversity among tissues tested, the enzymes obtained from various sources reveal similar physical and kinetic properties, and are capable of activating as Ca2+-activated, phospholipid-dependent protein kinase by limited proteolysis. The enzyme has a pH optimum at 7.5 to 8.0 and a molecular weight of about 8.8 X 10(4). The enzyme in its purified form is very sensitive to leupeptin and other thiol-protease inhibitors, but that in crude preparations is far less susceptible to the same inhibitors.

This indicates that butyrate or phenylbutyrate have antifibrogenic effects in human pterygium fibroblasts and could be novel types of prophylactic and/or therapeutic drugs for pterygium, especially phenylbutyrate, which does not have the unpleasant smell associated with butyrate.

Glycogen phosphorylase kinases in soluble fractions of various rat tissues were examined for the pH 6.8/8.5 activity ratio, Ca2+-dependency, activation by cyclic AMP-dependent protein kinase (protein kinase A), and reactivity with anti-skeletal muscle phosphorylase kinase serum. The enzymes could be divided into at least two major groups; muscle and liver types. The muscle type, that has a low value of pH 6.8/8.5 activity ratio, is highly dependent on Ca2+, markedly activated by protein kinase A, and strongly inhibited by the antiserum. Inversely, the liver type, that has a high value of pH 6.8/8.5 activity ratio, is poorly dependent on Ca2+, not activated by protein kinase A, and weakly inhibited by the antiserum. The enzymes from heart and skeletal muscle were similar and belonged to the former entity. Whereas, the enzymes from liver, kidney, spleen, lung, and testis appeared to belong to the latter entity. The enzyme from brain apparently differs from these entities, and seems to be an intermediate type or a hybrid of the two.

Polylysine greatly stimulated the autophosphorylation of phosphorylase kinase from rabbit skeletal muscle. When fully autophosphorylated, about 14 mol of phosphate per tetramer (αβγδ) were incorporated in the presence of polylysine, which was twice as much as those observed without polylysine. In contrast to this stimulatory effect of polylysine on the autophosphorylation, polylysine strongly inhibited the conversion reaction of phosphorylase b to a. The inhibition is competitive with a K i of 2.3 μg/ml. No effects of polylysine were observed on the activities of phosphorylase and cAMP‐dependent protein kinase.