EMBRYONIC HEMOGLOBIN SYNTHESIS
97
biologist is profound. Certainly the instructions of the genome, probably
in the form of messenger RNA, may form a basis for a search for control
of progressive cell specialization. This is not sufficient, however. The time
and place of new biosynthesis may also depend on other factors affecting
the process of protein synthesis; in the case of Hb it seems likely that
cofactors such as iron and heme may play a vital role.
D. Heterogeneity of Hemoglobin
Hemolysates obtained from any given animal rarely, if ever, contain
only 1 type of Hb. In the normal human adult, small amounts of another
Hb (A 2 ) are present. Furthermore the newborn also contains substantial
amounts of HbF. In these cases it is known that the heterogeneity is due
to differences of amino acids in the ß subunit class, being replaced by a
δ-chain for HbA 2 and a γ-chain for HbF. The various human Hb
anomalies are often due to amino acid substitutions in one of the types
of globin chains. This phenomenon of heterogeneity is widespread, and
perhaps universal, among vertebrates. There are the possible artifacts
of Hb polymerization or aggregation, and changes of the ferrous iron
of heme to ferric iron (methemoglobin), which can produce apparent
heterogeneity; but even when these artifacts are excluded, extensive
heterogeneity has been demonstrated. Heterogeneity of avian and frog
Hb is well known, and it will be useful to consider the present state of
our knowledge of these Hb's prior to a discussion of the controls exerted
over their synthesis in embryos.
1. Chickens
a. Adults. It has been known for some time that adult chicken hemolysates contain more than one Hb type. It is easy to separate 2 Hb
classes by chromatography (van der Helm and Huisman, 1958; Fraser,
1961; Manwell et al y 1963; Simons, 1965) or electrophoresis [Wilt, 1962
(agar) ; D'Amelio and Salvo, 1959b (starch block) ; Saha et al, 1955,
1957 (paper); Fraser, 1964a; Deuchar and Dryland, 1964 (cellulose
acetate) ; Müller, 1961 ; Manwell et al, 1963 (starch gel) ; Hell, 1966
(disc electrophoresis)]. The amino acid composition of the two components differs (van der Helm and Huisman, 1958). Furthermore,
D'Amelio and Salvo (1959b) and Manwell et al. (1963) have found a
third minor component by electrophoresis, and Fraser (1964a) and Hell
(1966) have recently confirmed this. Rodman and Ebaugh (1957) indicated the occasional detection of a third component many years ago.
D'Amelio and Salvo (1959a) found that the predominant Hb type mentioned above is in the erythrocyte nucleus, and furthermore that the
minor third Hb component is immunologically distinguishable from the
other two Hb types. Borgese and Bertles (1965) found 2 classes of Hb
97
biologist is profound. Certainly the instructions of the genome, probably
in the form of messenger RNA, may form a basis for a search for control
of progressive cell specialization. This is not sufficient, however. The time
and place of new biosynthesis may also depend on other factors affecting
the process of protein synthesis; in the case of Hb it seems likely that
cofactors such as iron and heme may play a vital role.
D. Heterogeneity of Hemoglobin
Hemolysates obtained from any given animal rarely, if ever, contain
only 1 type of Hb. In the normal human adult, small amounts of another
Hb (A 2 ) are present. Furthermore the newborn also contains substantial
amounts of HbF. In these cases it is known that the heterogeneity is due
to differences of amino acids in the ß subunit class, being replaced by a
δ-chain for HbA 2 and a γ-chain for HbF. The various human Hb
anomalies are often due to amino acid substitutions in one of the types
of globin chains. This phenomenon of heterogeneity is widespread, and
perhaps universal, among vertebrates. There are the possible artifacts
of Hb polymerization or aggregation, and changes of the ferrous iron
of heme to ferric iron (methemoglobin), which can produce apparent
heterogeneity; but even when these artifacts are excluded, extensive
heterogeneity has been demonstrated. Heterogeneity of avian and frog
Hb is well known, and it will be useful to consider the present state of
our knowledge of these Hb's prior to a discussion of the controls exerted
over their synthesis in embryos.
1. Chickens
a. Adults. It has been known for some time that adult chicken hemolysates contain more than one Hb type. It is easy to separate 2 Hb
classes by chromatography (van der Helm and Huisman, 1958; Fraser,
1961; Manwell et al y 1963; Simons, 1965) or electrophoresis [Wilt, 1962
(agar) ; D'Amelio and Salvo, 1959b (starch block) ; Saha et al, 1955,
1957 (paper); Fraser, 1964a; Deuchar and Dryland, 1964 (cellulose
acetate) ; Müller, 1961 ; Manwell et al, 1963 (starch gel) ; Hell, 1966
(disc electrophoresis)]. The amino acid composition of the two components differs (van der Helm and Huisman, 1958). Furthermore,
D'Amelio and Salvo (1959b) and Manwell et al. (1963) have found a
third minor component by electrophoresis, and Fraser (1964a) and Hell
(1966) have recently confirmed this. Rodman and Ebaugh (1957) indicated the occasional detection of a third component many years ago.
D'Amelio and Salvo (1959a) found that the predominant Hb type mentioned above is in the erythrocyte nucleus, and furthermore that the
minor third Hb component is immunologically distinguishable from the
other two Hb types. Borgese and Bertles (1965) found 2 classes of Hb