1 1 . M U C O P O L Y S A C C H A R I D E S IN TISSUE C U L T U R E
377
D. P A T H W A Y S OF M U C O P O L Y S A C C H A R I D E B I O S Y N T H E S I S
In mammalian tissues, as in bacteria (Roseman, Moses, Ludoweig
and Dorfman, 1953, 1954; Topper and Lip ton, 1953) and moulds
(Leloir and Cardini, 1953), both the hexosamine and uronic acid
components of the acid mucopolysaccharides are derived directly
from glucose, i.e. without cleavage of the carbon chain (Becker and
Day, 1953; Rieder and Buchanan, 1958a; Roden and Dorfman, 1958).
Synthesis of the hexosamine from glucose has been demonstrated
in vitro as well as in vivo. Thus Pogell (1959) observed the incorporation
of
1 4
C into glucosamine and galactosamine of the polysaccharides of
adult bovine corneas which were shaken in air with uniformly labelled
1 4
C-D-glucose and L-glutamine in Krebs-Ringer bicarbonate.
In many respects, organ cultures represent an improved form of the
biochemist's in vitro system. It is not surprising, therefore, that Lucy,
W e b b and Biggers (1961) found that both glucosamine and galactosamine were synthesized efficiently and directly from l1 4
C-glucose
in cultures of cartilaginous chick limb-bone rudiments cultivated in
a chemically defined medium.
The synthesis of galactosamine from glucose probably occurs via
glucosamine and not galactose. Thus, the transformation of jV (-acetyl-)
glucosamine as a U D P derivative to UDP-jV-acetyl-galactosamine has
been observed by Cardini and Leloir (1957). Sialic acid also appears
to be derived from D-glucosamine; the synthesis of jV-acetyl mannosamine from UDP-JV-acetyl glucosamine has been demonstrated by
Glaser (1960), whilst Kohn, Winzler and Hoffmann (1962) have
postulated the following steps: JV-acetyl glucosamine-6-P->jV-acetylD-mannosamine-6-P ->JV-acetylneuraminic acid-9-P.
The pathway of glucuronic acid synthesis (i.e. U D P - g l u c o s e — > U D P
glucuronic acid) is well defined, and recently Jacobson and Davidson
(1962) have isolated an enzyme, uridine diphosphate-D-glucuronic acid5-epimerase, from rabbit skin that catalyses the conversion of U D P - D -
glucuronic acid to L-iduronic acid.
Although glucose is present almost invariably in tissue culture
media and thus is the usual precursor of the component sugars of the
mucopolysaccharides, other carbohydrates, when these can be used
as energy sources, can be utilized in mucopolysaccharide synthesis.
Chang (1960), for example, showed that "ribose variants", isolated
from cultures of human conjunctival cells, were able to synthesize
mucopolysaccharides from the pentose more efficiently than the parent
strain.
It seems that the nitrogen of glucosamine may be derived from
either ammonia (Rieder, 1953; Rieder and Buchanan, 1958b), or
377
D. P A T H W A Y S OF M U C O P O L Y S A C C H A R I D E B I O S Y N T H E S I S
In mammalian tissues, as in bacteria (Roseman, Moses, Ludoweig
and Dorfman, 1953, 1954; Topper and Lip ton, 1953) and moulds
(Leloir and Cardini, 1953), both the hexosamine and uronic acid
components of the acid mucopolysaccharides are derived directly
from glucose, i.e. without cleavage of the carbon chain (Becker and
Day, 1953; Rieder and Buchanan, 1958a; Roden and Dorfman, 1958).
Synthesis of the hexosamine from glucose has been demonstrated
in vitro as well as in vivo. Thus Pogell (1959) observed the incorporation
of
1 4
C into glucosamine and galactosamine of the polysaccharides of
adult bovine corneas which were shaken in air with uniformly labelled
1 4
C-D-glucose and L-glutamine in Krebs-Ringer bicarbonate.
In many respects, organ cultures represent an improved form of the
biochemist's in vitro system. It is not surprising, therefore, that Lucy,
W e b b and Biggers (1961) found that both glucosamine and galactosamine were synthesized efficiently and directly from l1 4
C-glucose
in cultures of cartilaginous chick limb-bone rudiments cultivated in
a chemically defined medium.
The synthesis of galactosamine from glucose probably occurs via
glucosamine and not galactose. Thus, the transformation of jV (-acetyl-)
glucosamine as a U D P derivative to UDP-jV-acetyl-galactosamine has
been observed by Cardini and Leloir (1957). Sialic acid also appears
to be derived from D-glucosamine; the synthesis of jV-acetyl mannosamine from UDP-JV-acetyl glucosamine has been demonstrated by
Glaser (1960), whilst Kohn, Winzler and Hoffmann (1962) have
postulated the following steps: JV-acetyl glucosamine-6-P->jV-acetylD-mannosamine-6-P ->JV-acetylneuraminic acid-9-P.
The pathway of glucuronic acid synthesis (i.e. U D P - g l u c o s e — > U D P
glucuronic acid) is well defined, and recently Jacobson and Davidson
(1962) have isolated an enzyme, uridine diphosphate-D-glucuronic acid5-epimerase, from rabbit skin that catalyses the conversion of U D P - D -
glucuronic acid to L-iduronic acid.
Although glucose is present almost invariably in tissue culture
media and thus is the usual precursor of the component sugars of the
mucopolysaccharides, other carbohydrates, when these can be used
as energy sources, can be utilized in mucopolysaccharide synthesis.
Chang (1960), for example, showed that "ribose variants", isolated
from cultures of human conjunctival cells, were able to synthesize
mucopolysaccharides from the pentose more efficiently than the parent
strain.
It seems that the nitrogen of glucosamine may be derived from
either ammonia (Rieder, 1953; Rieder and Buchanan, 1958b), or