376
J. T. DINGLE AND M. WEBB
amount of mucopolysaccharide was bound to the cell, and that this
quantity tended to increase when the growth rate was low or the cell
density high. He did not differentiate between material located intracellularly and that bound to the cell surface. Daniel et al. (1961) have
shown that although repeated washings of a monolayer of rat fibroblasts contained no hyaluronic acid, trypsinization of these cells released
a considerable amount of this mucopolysaccharide. This would indicate
that some hyaluronic acid is associated with protein components of
the cell surface. If these macromolecules are firmly bound, and extend
into the protein polysaccharide components of the matrix, they may
relate the cell very closely to the structural elements of connective
tissue. In vitro they may be responsible at least in part for the adhesion
of the cell to surfaces. As discussed earlier, this polysaccharide, or
protein polysaccharide complex, associated with the cell would bind
water molecules and influence considerably the transport of ionic
material and metabolites. Thus, the effective "cell surface" might be
a considerable distance from the classical lipoprotein membrane of the
cell. The probable importance of the association of these macromolecules and water with the cell surface has been pointed out by a number
of authors, and the difficulty in delineating the biological cell surface
has been emphazised recently by Weiss (1962).
Weiss (1961) states that "it is a common observation that a mucoid
material is liberated from mammalian cells by trypsin treatment",
and, from studies on the effect of neuraminidase on the release of rat
dermal fibroblasts from a glass surface, concludes that sialic acid is also
an important structural component of the cell surface of this and
possibly other cell strains. It is unfortunate, however, that these results
are not entirely unequivocal, since 15% bovine serum was included
in the otherwise chemically defined medium used for the preliminary
culture of the cells. It is possible that adhesion of the cells may be
associated with sialoglycoprotein derived from the serum. In favour
of his conclusions, however, sialic acid (and thus sialoprotein) has been
located on the stroma surface of erythrocytes from various mammalian
species (Eylar, Brody and Oncley, 1961; Madoff and Eylar, 1961), on
the Ehrlich ascites carcinoma cell (Wallach and Eylar, 1961) and on
the blood cells of the lamprey(Petromyzon marinas) (Eylar, Doolittle and
Madoff, 1962), and has been shown to make a major contribution to
the negative surface-charge of these cells. In addition, Makela, Miettinen and Pesola (1960), for example, have found that trypsin treatment
of human red blood cells caused the release of about 50% of the sialic
acid and 15% of the hexosamine from the cells. Cook, Heard and
Seaman (1960) also reported the liberation of a sialomucopeptide from
human red blood cells on treatment with trypsin.
J. T. DINGLE AND M. WEBB
amount of mucopolysaccharide was bound to the cell, and that this
quantity tended to increase when the growth rate was low or the cell
density high. He did not differentiate between material located intracellularly and that bound to the cell surface. Daniel et al. (1961) have
shown that although repeated washings of a monolayer of rat fibroblasts contained no hyaluronic acid, trypsinization of these cells released
a considerable amount of this mucopolysaccharide. This would indicate
that some hyaluronic acid is associated with protein components of
the cell surface. If these macromolecules are firmly bound, and extend
into the protein polysaccharide components of the matrix, they may
relate the cell very closely to the structural elements of connective
tissue. In vitro they may be responsible at least in part for the adhesion
of the cell to surfaces. As discussed earlier, this polysaccharide, or
protein polysaccharide complex, associated with the cell would bind
water molecules and influence considerably the transport of ionic
material and metabolites. Thus, the effective "cell surface" might be
a considerable distance from the classical lipoprotein membrane of the
cell. The probable importance of the association of these macromolecules and water with the cell surface has been pointed out by a number
of authors, and the difficulty in delineating the biological cell surface
has been emphazised recently by Weiss (1962).
Weiss (1961) states that "it is a common observation that a mucoid
material is liberated from mammalian cells by trypsin treatment",
and, from studies on the effect of neuraminidase on the release of rat
dermal fibroblasts from a glass surface, concludes that sialic acid is also
an important structural component of the cell surface of this and
possibly other cell strains. It is unfortunate, however, that these results
are not entirely unequivocal, since 15% bovine serum was included
in the otherwise chemically defined medium used for the preliminary
culture of the cells. It is possible that adhesion of the cells may be
associated with sialoglycoprotein derived from the serum. In favour
of his conclusions, however, sialic acid (and thus sialoprotein) has been
located on the stroma surface of erythrocytes from various mammalian
species (Eylar, Brody and Oncley, 1961; Madoff and Eylar, 1961), on
the Ehrlich ascites carcinoma cell (Wallach and Eylar, 1961) and on
the blood cells of the lamprey(Petromyzon marinas) (Eylar, Doolittle and
Madoff, 1962), and has been shown to make a major contribution to
the negative surface-charge of these cells. In addition, Makela, Miettinen and Pesola (1960), for example, have found that trypsin treatment
of human red blood cells caused the release of about 50% of the sialic
acid and 15% of the hexosamine from the cells. Cook, Heard and
Seaman (1960) also reported the liberation of a sialomucopeptide from
human red blood cells on treatment with trypsin.