A chymotrypsin-like proteinase that may be involved in desquamation in plantar stratum corneum

We have recently reported that unipolar cell shedding from plantar stratum corneum incubated in vitro, and the associated degradation of the desmosomal protein desmoglein I, are dependent on the activity of a proteinase that can be inhibited by aprotinin, chymostatin and zinc ion. The aim of this work was to find a proteinase in plantar stratum corneum that fulfils the criteria for being the responsible enzyme. Dissociated plantar corneocytes were incubated with the chymotrypsin substrate 3-carbomethoxypropionyl-L-Arg-L-Pro-L-Tyr-p-nitroanilide hydrochloride (S-2586) and H-D-Ile-Pro-Arg-p-nitroanilide dihydrochloride (S-2288), a substrate for a wide range of serine proteinases with arginine specificity. There was a significant rate of hydrolysis of S-2586, but S-2288 was hydrolysed only very slowly. Extraction of dissociated corneocytes with buffers containing KCl or sodium dodecyl sulphate released one major proteinase that could be detected by electrophoresis in polyacrylamide gels with copolymerized casein and subsequent incubations of the gels. Both the caseinolytic activity and the S-2586-hydrolysing activities were inhibited by aprotinin, chymostatin and zinc ion, but not by leupeptin. The S-2586-hydrolysing activity was also inhibited by soybean trypsin inhibitor and phenylmethylsulphonyl fluoride. Both activities were optimal at pH 7-8 but were also significant at pH 5.5. On gel exclusion chromatography, the S-2586-hydrolysing and caseinolytic activities were eluted with an apparent molecular weight of around 18 kDa. When analyzed by electrophoresis in the presence of sodium dodecyl sulphate under non-reducing conditions the caseinolytic enzyme had an apparent molecular weight of around 25 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)