Digestive endo-proteases from the midgut glands of the Indian white shrimp, Penaeus Indicus (Decapoda: Penaeidae) from Kenya
In order to provide information on the digestive capacity of marine crustacea of mariculture potential in Kenya with a view to aiding the development of suitable feeds to support the industry, a biochemical survey was made of enzymes of extracellular digestion in the Indian White shrimp, Penaeus indicus. Results showed midgut gland endo-proteases in wild adult shrimp from the Kenya coast to have optima between pH 7.2 and 8.5 (Trypsin pH 7.5-8.0, Chymotrypsin pH 7.2-7.8, Elastase pH 6.8-8.5) with maximum specific activities of 101-408, 37-516, 70-90 Units mg protein-1 min-1 for trypsin, chymotrypsin and elastase respectively. There was no pepsin. The North Sea Norway lobster, Nephrops norvegicus, was investigated to a lesser extent and found to have much lower trypsin activity than the shrimp and no chymotrypsin. In addition to the cited serine endo-proteases, significant activity in the shrimp was thought to originate from non-serine proteases. This situation may differ from other shrimps in which serine endo-protease activity, especially trypsin, is dominant. Diphenylcarbamyl chloride (DPCC) and 2-Nitro-4-Carboxyphenyl N,N-Diphenylcarbamate (NCDC) inhibited chymotrypsin but not trypsin, Soybean Trypsin Inhibitor (SBTI), Bowman-Birk Chymotrypsin-Trypsin Inhibitor (BBSTCI), N-Tosyl-L-Phenylalanine Chloromethyl Ketone (TPCK), 4-(2-Aminoethyl)-Benzenesulfonylfluoride Hydrochloride (AEBSF) and N-Tosyl-Llysine Chloromethyl Ketone/1-Chloro-3-Tosylamido-7-Amino-L-2-Heptanone Hydrochloride (TLCK) inhibited both, while Phenyl Methanesulfonyl Fluoride/ Phenylmethyl Sulfonyl Fluoride/ á-Toluenesulfonyl Fluoride (PMSF) and Ovomucoid Trypsin Inhibitor (Ovomucoid/OTI) precipitated shrimp homogenate. The effect of the former was inferred from the action of AEBSF which together with TLCK inhibited shrimp trypsin more than chymotrypsin. In contrast, TPCK inhibited shrimp chymotrypsin more than trypsin. These results indicate that relying on imported commercial feeds, usually developed for other species or strains of farmed shrimp in other parts of the world, may not only be too uneconomical but may not provide adequate nutrition to local animals if not efficiently digested. There is, therefore, greater need and urgency to establish detailed enzymic profiles and digestive capacities of locally cultured fin and shellfish. Such studies should parallel those prospecting for suitable feed ingredients while developing local capacity for feed technology.