FOOD-STIMULATED SYNTHESIS OF INTESTINAL PROTEOLYTIC ENZYMES IN COCKROACH LEUCOPHAEA MADERAE

In adult Leucophaea males and females high proteolytic activity is primarily found in the posterior region of the midgut lumen. Only feeding on rat food, casein, fibrin, glutenin, and elastin stimulated protease activity; several other proteins, casein hydrolysates, amino acids, some polyamino acids, and starch did not cause increased enzyme activity. A proportionality was found between the quantity of certain proteins passed into the midgut and the enzyme activity in the midgut. Since the rate of the food release from the crop into the midgut is higher the more food is eaten, the level of enzyme activity is positively related to the amount of food consumed during one meal. The first increase in enzyme activity was observed about 12 to 14 hr after feeding; the enzyme level stayed high for approximately 1·5 days and then decreased again. After injection of 14C-leucine into fed or starving animals, fractionation on Sephadex G-150 revealed that only the enzyme fractions of fed animals were appreciably labelled; little label was found in the enzyme fractions from starving animals. This is support for the hypothesis that proteinaceous foods stimulate protease synthesis rather than activate a precursor. No control of enzyme synthesis appears to be exerted by hormones from the brain (neurosecretory cells), corpora cardiaca, or corpora allata since removal of these organs before or after feeding had no effect on protease production in the midgut. However, severance of the innervation of the proventricular valve caused a reduction of enzyme synthesis because food passage was impaired after this operation. It is concluded that stimulation of protease synthesis in the midgut is solely secretagogue. A powerful inhibitor for the cockroach protease in found in the anterior midgut and the caeca. It is apparently produced in the caeca at a high rate. Its characteristics are similar to those of soy bean trypsin inhibitor; it is heat-stable, non-dialysable, can be digested by pronase and the animal's own proteases, and is precipitable by ammonium sulphate. It is thus likely that the inhibitor is a heat-stable protein. © 1969.