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.

Pectic polysaccharides of growing plant tissues

1. The polysaccharide compositions of the cell walls of sycamore cambium and sycamore callus tissue have been analysed and found to be directly comparable. 2. Electrophoretic analyses of the whole pectins prepared from actively growing callus and cambial tissue have shown that these preparations contain, in addition to the neutral and weakly acidic components present in apple fruit, a strongly acidic polygalacturonic acid component. 3. The weakly acidic component of all the pectins was directly comparable with that of the pectinic acid of apple fruit. 4. The components of the whole pectin of sycamore callus tissue have been partially purified and analysed. The neutral and weakly acidic components also found in apple fruit were isolated. 5. The pattern of the composition of the neutral sugars present in the pectins of actively growing tissues of cambium and callus has been compared with those present in apple-fruit pectinic acid. 6. The presence of rhamnose linked as galacturonosyl-(1-->2)-rhamnose has been found in sycamore whole pectin. 7. The difference in the pectins of callus, cambium and fruit appears not to be that of species difference but is more characteristic of the nature of the growth and growth conditions of the cells. This is discussed in relation to the problems of the control and mechanism of plant-cell growth and differentiation.