Cytochemical study of macrophage lysosomal inorganic trimetaphosphatase and acid phosphatase

Cytochemical investigations have associated acid inorganic trimetaphosphatase (TMPase) activity with the lysosomes of certain cell types. We have used the modified staining technique of Berg to show that this enzyme activity is present in normal mononuclear phagocytes and macrophage cell lines. We have found this enzyme activity to be present in murine RAW264 macrophages, in human U937 macrophages, in normal human blood monocytes, and in guinea pig peritoneal macrophages. All of the RAW264 and U937 macrophages showed intense TMPase activity. Many of the human monocytes and most of the guinea pig macrophages were labeled by this method. The reaction product was associated with the lysosomes of these cell types. The lysosomal staining-pattern was similar to that of acid phosphatase. Differences with regard to Golgi staining were noted. This indicates that TMPase is a lysosomal enzyme of mammalian macrophages. The distinction between TMPase and acid phosphatase activity has been demonstrated by measuring the pH optimum of each enzyme. Using substrates identical to those of the ultrastructural cytochemistry, we show that the pH optimum of TMPase is 4.0 and that of acid phosphatase is 5.0. The enzymatic activities are therefore ultrastructurally and biochemically distinct. Following phagocytosis of latex, yeast (Saccharomyces cerevisiae), or Corynebacterium parvum, TMPase has been found to be associated with phagosomes. This enzyme may take part in the degradation of phagocytosed materials, particularly microorganisms which contain inorganic polyphosphates and metaphosphates.