The histological localization of renin with fluorescent antibody

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Simultaneous hydrolyses of esters and proteins at saturation levels

A direct titration method for the determination of proteolytic activity is discussed. This involves the potentiometric measurement of the volume of 0.08 N NaOH required to maintain a constant pH (8.0) during the time of the hydrolysis. It is a sensitive method which presents several advantages; viz., it measures simultaneously protease and esterase activity, it follows the hydrolysis very closely and from the first stages; the titration is continuous and on the same sample. This method determines a constant fraction of the groups titratable by formol titration. The ratio formol: direct titration is represented by a factor "f" which is presumed to be distinct for each protein-enzyme system. Kinetic studies, using this method, revealed that the rates of hydrolysis of mixtures casein-gelatin on one hand, casein-BAEE or gelatin-BAEE on the other, are always larger than those of the corresponding isolated substrates. In many cases the resulting rates are equal or nearly equal to the sum of the individual rates, even though the mentioned rates have been determined within the saturation zones for every substrate. The former observations are inconsistent with the theory of the formation of an intermediary enzyme-substrate compound, unless it is assumed that the enzyme has a specific active group for each substrate.

The histochemical demonstration of leucine aminopeptidase

1. A method is described for the histochemical localization of leucine aminopeptidase in fresh frozen and paraffin embedded tissues.

2. Evidence is offered which supports the idea that the substrate l-leucyl-β-naphthylamide is hydrolyzed by leucine aminopeptidase.

3. A comparison is made between the various diazonium salts used to demonstrate the enzyme in tissue sections. The shortcomings of each coupling agent are given. While the one recommended in this report has many favorable properties, its slow rate of coupling constitutes a serious drawback in localization at the cellular level. Experiments are in progress to overcome this deficiency in the method.

4. The value and future potential of chelations with metal ions in histochemical methodology is discussed.

5. Leucine aminopeptidase was found to be present histochemically in many organs of man, guinea pig, dog, and rat.