Distribution, specificity and function of some proteases, general esterases and cholinesterases from several species of starfish

Abstract

1. 1. The distribution and pattern of proteases, lipases and esterases in extracts from the pyloric caeca and skin of several species of starfish have been determined by starch gel electrophoresis coupled with specific staining. In Asterias rubens the cardiac stomach, intestine and rectal sacs were also investigated. 2. 2. Most protease activity originates in the caecae. The skin of A. rubens contained insignificant activity towards artificial protease substrates, but while that of Solaster papposus was about 10 per cent of the caecal level, it would not digest gelatin. The significance of these findings for external digestion is discussed. 3. 3. The proteases are first formed as inactive zymogens and become spontaneously active after extraction. The number of bands resolved by electrophoresis increases in the first day of extraction and then remains constant. 4. 4. Using artificial substrates and specific inhibitors, distinct trypsin and chymotrypsin-like activities could be demonstrated in tissue extracts. Their distribution in various species is reported. Two bands of trypsin, two bands of chymotrypsin and one band of p-nitrophenylacetate esterase could be resolved in extracts of A. rubens by electrophoresis on Sephadex blocks. Michaelis constants and other properties of the partially purified enzymes and those in crude extracts are reported. 5. 5. In caecal extracts tributyrin esterase showed two bands of activity on starch gel and these corresponded to the major bands of p-nitrophenyl acetate esterase activity. Triolein esterase activity was weaker and corresponded with the most electropositive of the other esterase bands. These esterase activities were distinct from the protease activity. A. rubens skin esterase was inactive with p-nitrophenyl acetate. 6. 6. Extracts were also investigated for the presence of enzymes similar to human acetylcholine esterase and serum cholinesterase. Evidence was obtained for an acetylcholinesterase which is tentatively suggested to be involved in nervous function.