The agar cup-plate ' diffusion technique has been applied to the quantitative determination of enzyme activity, principally to amylase, polygalacturonase, cellulase. protease and pectin-esterase. With all enzymes so far examined, the relationship between diameter of zone and log(amount of enzyme) is linear over a wide range, and may be used for the quantitative estimation of the enzymes. The cup-plate assay of polygalacturonase, like viscometric methods, measures the initial destruction of the colloidal properties of pectic acid, and, owing t o the complex nature of polygalacturonase, bears no simple relationship t o the assay of polygalacturonase by the estimation of glycosidic hydrolysis. H. Experiments are described in which flour stored in jute bags, the fabric of which had been impregnated with insecticides, was exposed to infestation by the species Ephestia kuhniella, Ptinus tectus and Tribolium confusum. The use of 1 % (w/w) of DDT in the fabric provided good protection against the first two named, and fair, but by no means absolute, protection against T . confusum. Transfer of insecticide to the flour occurred to an extent sufficient to be classed as contamination.
1. Antisera were raised against lysosomal cathepsin D of man, chicken and rabbit. 2. The antisera were found to be specific and potent inhibitors of cathepsin D activity. 3. The immunological nature of the inhibition was established. 4. The inhibitory effect was studied by varying pH, antiserum/enzyme ratio, time of incubation, concentration of components and order of mixing, and by using purified antibody and univalent antibody fragments. 5. The specificities of the antisera were examined with respect to other enzymes, isoenzymes of cathepsin D and cathepsin D from different organs. 6. The antisera prevented the action ofcathepsin D on isolated proteoglycans and on cartilage. 7. The antisera produced up to 90% inhibition of the autolysis of cartilage from chicks and rabbits, indicating that cathepsin D is the enzyme mainly responsible for the breakdown of proteoglycans in this system.
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