Differential Centrifugation Studies of Guinea Pig Lung Proteases

Summary Five subcellular fractions were isolated from guinea pig lung homogenates by differential centrifugation. These fractions were defined biochemically by the analysis of 18 enzymes representing different subcellular compartments. Succinate dehydrogenase and cytochrome oxidase distributed with the heavy mitochondrial fraction, while N-acetyl-β-glucosaminidase, acid p-nitrophenylphos-phatase, cathepsins A, Bl, and D, dipeptidyl-peptidases I and II, and elastolytic esterase distributed with the light mitochondrial fraction. Alkaline p-nitrophenylphosphatase, glucose 6-phosphatase, dipeptidylpeptidase IV, neutral protease, and alkaline protease all demonstrated a “microsomal” enrichment. In the cytosol were found lactate dehydrogenase, dipeptidylpeptidase III, and a dipeptidase. The lung subcellular fractions were heterogeneous with cross-contamination between the heavy mitochondrial, light mitochondrial, and “microsomal” fractions. The enzyme distributions noted were similar to those found in other tissues.