David M. Glick

A pepsinogen from rainbow trout

1. A pepsinogen, Ia on the basis of its electrophoretic mobility, from rainbow trout stomach, has an optimum pH near 2 for activation. 2. The cognate pepsin is denatured at pH values above 7, in contrast to the zymogen, which is slightly more alkali-stable. It has an optimum pH of 3 for proteolysis of denatured hemoglobin. 3. The intrinsic reactivity of the zymogen and pepsin (rates of activation and of proteolysis, respectively) are quite high, but as they operate at the environmental temperature of the fish, are remarkably similar to rates of activation and proteolysis by mammalian pepsinogens and pepsins.

A pepsinogen from dog stomach

1. A pepsinogen has been purified from dog stomach in 20% yield. 2. At pH values below 4 it spontaneously converts to a pepsin, the first order rate constant at pH 2, 22 degrees C, being 11 min-1. 3. The pepsinogen is stable to denaturation at pH values up to 9, in contrast to the pepsin which is irreversibly denatured above pH 7. 4. Its proteolytic activity against denatured hemoglobin is equal to that of pig pepsin, but in the milk-clotting assay at pH 5.5 its has only 14% the activity.

Stimulated chloride transport by isolated parietal cells

Abstract A preparation of rabbit parietal cells has been shown to respond to effectors of gastric acid secretion. The cells were isolated, aligned at the interface of two aqueous phases, and the transport of Cl− from one phase to the other effected by the cells under various pharmacological stimuli, was measured. Ca2+, in contrast to Mg2+, was shown to be necessary to elicit a response with histamine. This response was inhibited by prostaglandin E1. Dibutyryl cyclic AMP was without effect. Carbachol and catecholamines also stimulated secretion, but this was not inhibited by prostaglandin E1. Because basal Cl− transport in the presence of Ca2+ is in a direction opposite to that of the stimulated transport (and to the low basal transport in the presence of Mg2+), at least two secrection mechanisms appear operative.

Effects of solutes on the temperature dependence of chymotryptic hydrolysis

Abstract Contrary to published reports, chymotrypsin is sensitive to the nature of the solute accompanying it in solution. This is seen in the temperature dependence of its hydrolysis of N- acetyl- l -tyrosine ethyl ester in 9 different solutions. Despite the variation in temperature dependence as a function of the solute, there exists a temperature, near 25°, where the rate is insensitive to the solute. This constitutes an example of linear entropic compensation for enthalpy in the rate determining step of catalysis. The results are considered in relation to the known thermally-induced conformational change that chymotrypsin undergoes at 25°.

On the activation of the canine pepsinogens

Acidification induces a conversion of canine pepsinogens by a sequential mechanism to the active pepsins. Activation in the presence of pepstatin, which strongly inhibits the pepsins but does not prevent the first step of activation, allows the isolation of the peptide released in this first step. This peptide inhibits the milk clotting activity of canine and also porcine pepsin. Canine pepsins obtained in the absence of pepstatin were characterized by amino acid composition, molecular weight, and activity against hemoglobin and milk and compared with those of other mammalian pepsins.