Lysosomal acid proteinase of rabbit liver

1. Acid proteinase from rabbit liver lysosomes was purified about 1000-fold, on a protein basis. 2. The purification procedure involved isolation of a lysosomal-mitochondrial pellet and conversion of this into an acetone-dried powder. 3. The enzyme was extracted with an acidic buffer and subjected to column chromatography with DEAE-Sephadex and Sephadex G-100. 4. The molecular weight of the enzyme was 50000-52000. 5. Maximal activity against haemoglobin was obtained at pH3.2; serum albumin was attacked, but very much more slowly. 6. Several possible inhibitors of the enzyme were tested. Thiol-blocking reagents, several inhibitors of trypsin and chymotrypsin, and a chelating agent were without effect. 7. The enzyme was competitively inhibited by 3-phenylpyruvic acid at low concentrations. 8. Dithiothreitol caused rapid inactivation of the enzyme at pH8. 9. It is concluded that this enzyme is a form of cathepsin D, which may be widely distributed in lysosomes.

Effects of acute asphyxia and deep hypothermia on the state of binding of lysosomal acid hydrolases in canine cardiac muscle

The amount and state of binding of three lysosomal acid hydrolases, acid phosphatase, cathepsin, and β-glucuronidase, were studied in canine cardiac muscle following severe asphyxia and deep hypothermia. The studies were done on adult mongrel dogs anesthetized with sodium pentobarbital. Asphyxia was produced by tracheal occlusion, and was maintained until the onset of cardiac arrest (6 to 10 min). Hypothermic conditions were achieved by placing the heart on partial bypass through a heat exchanger. The heart was cooled to 6 to 10°C and held at this temperature for 30 min while circulation and respiration were maintained by artificial means. Control dogs were subjected to similar surgical procedures. Immediately following the experiments, the whole hearts were removed, cooled to 0 to 4°C, homogenized, and fractionated into supernatant and lysosomal fractions. The levels of bound and free acid hydrolases were estimated in the whole homogenates and fractions. Asphyxia produced a large shift of acid hydrolase activity from a bound form to a free form, as evidenced by elevated ratios of free to bound activity in the whole homogenates and elevated ratios of supernatant to lysosomal activity with respect to the fractions. Hypothermia did not alter the binding status of the lysosomal enzymes. These findings suggest that lysosomal enzymes play a major role in asphyxic damage to the heart.

Influence of glucagon, an inducer of cellular autophagy, on some physical properties of rat liver lysosomes

The response of rat liver lysosomes to an intraperitoneal injection of glucagon has been evaluated from studies on the mechanical fragility, osmotic sensitivity, and sedimentation properties of these subcellular particles. It has been found that about (1/2) hr after the injection of glucagon the hepatic lysosomes exhibit a fairly sudden increase in their sensitivity to mechanical stresses and to exposure to a decreased osmotic pressure. At the same time, their sedimentation properties undergo complex changes characterized mainly by a significant increase in the sedimentation coefficient of a considerable proportion of the total particles. In addition, glucagon causes an increase in the proportion of slowly sedimenting particles, with the result that the distribution of sedimentation coefficients within the total population tends to become bimodal. The latter change is more pronounced for acid phosphatase, less so for cathepsin D, and barely detectable for acid deoxyribonuclease. All these modifications are maximal between 45 and 90 min after injection and regress to normal within approximately 4 hr. With the exception of the increase in the slow component, for which no explanation can be advanced at the present time, they are consistent with the hypothesis that glucagon causes an increase in lysosomal size, and may be related to the autophagic-vacuole formation known to occur after glucagon administration.