The biological diversity of marine species provides a wide array of enzymes with unique properties. For this reason, there is great potential for the recovery and use of digestive proteases from fish provessing wastes. Fish digestive proteolytic enzymes most commonly studied include pepsin, trypsin, chymotrypsin, gastricsin and elastase. Enzymes from cold adapted ectothermic organisms have application in the food industry because their temperature and other characteristics differ from homologous proteases from warm‐blooded animals. The South‐West Atlantic ocean is an enormous reservoir of different fish species. The digestive proteases from these organisms can be isolated as a by‐product and used for processing aids in the food industry.

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The effects of temperature on the apparent Michaelis-Menten constant (K,) of pyruvate were determined for M,-lactate dehydrogenases (LDHs) of 15 species of the teleost family Sciaenidae from habitats differing in average temperature and temperature range. The central question addressed was whether adaptive differences in the effect of temperature on an important kinetic parameter, K,, reflect selection based on the range of temperatures experienced by the species, the highest temperature encountered by the species, or both of these factors.For the M,-LDHs of all 15 species, the K, of pyruvate was conserved between 0.1 and 0.4 mM pyruvate over the species' physiological temperature range. However, large increases in K, of pyruvate commonly were found at temperatures a few degrees C above the species' upper habitat temperature. Distinctions were found between the responses of the enzymes of eurythermal and stenothermal sciaenids. For the most eurythermal species, e.g., Sciaenops ocellatus, Micropogonias undulatus, and Roncador stearnsii, K, of pyruvate varied only about twofold between 10 and 30"C, the temperatures which encompass most of the habitat ranges of these species. For the most stenothermal species, e.g., Cynoscion striatus and Micropogonias furnieri, with habitat temperature ranges of 14-18"C, sharp increases in K, occurred a t temperatures above 20°C. We hypothesize that thermal stability of K, values is more strongly selected by maximal habitat temperature than by the amount of variation in habitat temperature, and that adaptation to high temperatures may pre-adapt enzymes for eurythermal function.

A southwest Atlantic croaker protease was purified from the pyloric caeca by ammonium sulfate fractionation, acetone precipitation and affinity chromatography. The enzyme was classified as a trypsin on the basis of molecular weight, its ability to hydrolyze synthetic substrates N‐α‐benzoyl‐arginine‐p‐nitroanilide (BAPA) and tosylarginine methyl ester (TAME), and its inhibition by known trypsin inhibitors. The isolated enzyme has a single band on SDS‐PAGE with an estimated molecular mass of 24 kDa. Croaker trypsin activity was stable between pH 5 and pH 11 for 30 min at 0C, 10C and 25C and its maximal activity against BAPA was at pH 9.5. Thermostability was observed to about 55C for 30 min at pH 7.8 and its temperature optimum was 60C. Substrate turnover number was 850 BAPA units per μmol trypsin, and the Kmwas 0.081 mM at 25C. For the hydrolysis of TAME, Vmaxwas 9273 units per μmol trypsin and the Km was 0.155 mM at 25C. The catalytic efficiency Vmax/Kmwas higher than that of trypsin from fish living in colder waters.