9 . P R O T E I N M E T A B O L I S M IN C U L T U R E
311
at later stages (36-48 h). This reduction in enzyme activity was
apparently the result of the release of a protease inhibitor by the cells
(Tokuda, Hayashi and Matsuba, 1960). It was suggested that the
balance between protease and anti-protease release may determine
the intensity, extent and duration of certain sensitization phenomena.
Maeir (1961) has pointed out that enzymes provide convenient
markers in studies on the ingestion of protein by cultured cells since
the intracellular position of an enzyme can be determined histochemically if the enzyme remains functionally intact after ingestion.
Peritoneal monocytes from the guinea-pig were cultured in the presence
of peroxidase and the enzyme was subsequently demonstrated to be
present mainly in the perinuclear zone of the cells. Acid phosphatase,
characteristic of lysosomes, appeared in granules occupying the same
area as the peroxidase activity and it was suggested that this observation reflected attempted digestion of the ingested protein.
Observations have been made by Herrmann, Konigsberg and Robinson (1960) on cultures of normal and dystrophic muscle-tissue from the
chick. Although differences in the protein nitrogen of cultures of
dystrophic muscle and that of control cultures were found under
certain conditions, no positive indications were obtained for the cause
of muscular dystrophy. Recently, Tappel, Zalkin, Caldwell, Desai
and Shibko (1962) have reported evidence for the presence of lysosomes
in mouse and chicken skeletal muscle. Furthermore, increased net
activities of free and total lysosomal enzymes, including cathepsin,
were found in the muscle of genetically dystrophic mice and chicks.
Greatly elevated activities of lysosomal enzymes have also been noted
by these workers in vitamin E-deficient and dystrophic rabbits. They
suggest that increased lysosomal enzymes are the cause of hydrolytic
and catabolic wasting processes in muscular dystrophy. In view of the
observations mentioned above, which demonstrated that a lysosomal
protease is concerned in the dissolution of cartilage matrix in vitro
under the influence of an excess of vitamin A, it would appear that
a re-investigation of the behaviour of dystrophic muscle in culture may
be of value in further studies on the catabolic mechanisms involved
in muscle dystrophy.
V . C O N C L U S I O N
In this brief survey it has not been possible to review all the recent
work in which Tissue Culture has been employed in the study of the
amino acid and protein metabolism of animal cells. Nevertheless, it
may be seen that a very wide range of problems has been investigated
311
at later stages (36-48 h). This reduction in enzyme activity was
apparently the result of the release of a protease inhibitor by the cells
(Tokuda, Hayashi and Matsuba, 1960). It was suggested that the
balance between protease and anti-protease release may determine
the intensity, extent and duration of certain sensitization phenomena.
Maeir (1961) has pointed out that enzymes provide convenient
markers in studies on the ingestion of protein by cultured cells since
the intracellular position of an enzyme can be determined histochemically if the enzyme remains functionally intact after ingestion.
Peritoneal monocytes from the guinea-pig were cultured in the presence
of peroxidase and the enzyme was subsequently demonstrated to be
present mainly in the perinuclear zone of the cells. Acid phosphatase,
characteristic of lysosomes, appeared in granules occupying the same
area as the peroxidase activity and it was suggested that this observation reflected attempted digestion of the ingested protein.
Observations have been made by Herrmann, Konigsberg and Robinson (1960) on cultures of normal and dystrophic muscle-tissue from the
chick. Although differences in the protein nitrogen of cultures of
dystrophic muscle and that of control cultures were found under
certain conditions, no positive indications were obtained for the cause
of muscular dystrophy. Recently, Tappel, Zalkin, Caldwell, Desai
and Shibko (1962) have reported evidence for the presence of lysosomes
in mouse and chicken skeletal muscle. Furthermore, increased net
activities of free and total lysosomal enzymes, including cathepsin,
were found in the muscle of genetically dystrophic mice and chicks.
Greatly elevated activities of lysosomal enzymes have also been noted
by these workers in vitamin E-deficient and dystrophic rabbits. They
suggest that increased lysosomal enzymes are the cause of hydrolytic
and catabolic wasting processes in muscular dystrophy. In view of the
observations mentioned above, which demonstrated that a lysosomal
protease is concerned in the dissolution of cartilage matrix in vitro
under the influence of an excess of vitamin A, it would appear that
a re-investigation of the behaviour of dystrophic muscle in culture may
be of value in further studies on the catabolic mechanisms involved
in muscle dystrophy.
V . C O N C L U S I O N
In this brief survey it has not been possible to review all the recent
work in which Tissue Culture has been employed in the study of the
amino acid and protein metabolism of animal cells. Nevertheless, it
may be seen that a very wide range of problems has been investigated