| Abstract: | Using metabolic labelling and sucrose density fractionation we compared the synthesis of lysozyme and lysosomal enzymes in human monocytic U937 cells. In pulse-chase experiments in sucrose density gradients, the intracellular radioactively labelled lysozyme distributed similarly to cathepsin D and beta-hexosaminidase. With the aid of immunochemical detection in Western blots, the steady-state distribution of lysozyme was found to be slightly different from that of beta-hexosaminidase; relatively more lysozyme was present in fractions sedimenting between lysosomes and the Golgi apparatus. The observed distribution of the lysozyme antigen with a prominent peak in the lysosomal fraction was in striking contrast to the broad distribution of the lysozyme activity. The difference was explained by a bias in the determination of the activity of lysozyme by the 'lysoplate' diffusion assay. |
