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A new minor haemoglobin, L, was isolated from the haemolysates of chicken embryos more than 7 days old. Electrophoresis in denaturing conditions and tryptic peptide maps of the globins show that the β-Mike globin of HbL is identical to that of the minor haemoglobin H(βH) while the α-like globin is very similar to that of the adult haemoglobin D (αD). HbL completes the description of the map of the minor chicken haemoglobins during embryonic development. In early embryos two minor haemoglobins, M and E, are produced which have the same βMike globin (ε) and differ in their α-like globins (αD and αA, respectively). The same two α -like globins will make up the minor haemoglobins of the late embryo, L and H, which differ from HbM and HbE on account of their β -like globin (βH). The native tetramers L and M are hard to distinguish from each other. However the constituent ε globin can be easily separated from βH by electrophoresis on polyacrylamide gel in formic acid. With this method we found that the switch of the minor haemoglobins in the blood of chicken embryos starts at the 7th incubation day. The two red cell populations, primitive and definitive, present in the blood of 7-day-old embryos were separated on an albumin gradient and their minor haemoglobins analysed. The haemoglobin couple M/E was found in the primitive erythroid cells whereas the L/H couple was found in the definitive ones. The disappearance of the early haemoglobin couple and its substitution by the late one during embryonic development correlates with the replacement of erythroid lines in the blood.

Three haemoglobins were isolated by ion-exchange chromatography from the haemolysates of embryonic duck erythrocytes up to 8 days of development. The component globins were characterized both by electrophoresis in dissociating conditions and by finger-printing analysis. The major haemoglobin fraction El appears to be an embryonic tetramer since its constituent globins are different from all the others synthesized during embryonic and adult life. The two minor fractions E2 and E3 show a-type subunits that are very similar to those of the two adult haemoglobins Al and A2 respectively. They are present all through embryonic life, as demonstrated by chromatographic analysis. For these reasons they have been considered foetal. The two haemoglobins typical of the adult animal are found in the red cells of the embryo from 8 days of incubation. Their relative amounts change continuously during embryonic development and reach the adult value after hatching.

The synthesis of globins in the chick embryo before the onset of circulation has been studied in situ by specific immunofluorescence labelling of embryonic sections and by labelling newly synthesized proteins in ovo and in vitro in embryonic explants with [3H]leucine. The presence of major primitive haemoglobins is observed by 28 h of incubation. The minor primitive haemoglobins become detectable by immunofluorescence after 40 h of development, shortly before the onset of circulation. 3H-labelling shows that one definitive α chain is synthesized, though in low concentration, from the initial globin detection. The other definitive α chain is observed in embryos of at least 40 h of development. The relative concentration of the two definitive α chains changes rapidly with development indicating a specific mechanism of regulation. An erythropoietic site is observed in the wall of the dorsal aorta in embryos of about 45–50 h of development. From the initial detection, those cells contain all four primitive embryonic haemoglobins, in contrast to what is observed for the cells of the blood islands.

3 molecular forms (P1, P2 and P3) of acid phosphatase (E.C.3.1.3.2) have been detected in chicken liver homogenate. The different intracellular localization of these molecules has been demonstrated by cellular fractionation and electrophoretic analysis. P1 and P2 phosphatases are both present in the particulate fraction. P3 is present in a pure form in the soluble fraction. The difference between the enzyme molecules present in the particulate fraction and that in the soluble one is confirmed by the different activation-inhibition effect of various ions and substances on the enzymatic activity of subcellular fractions.

The molecular heterogeneity of acid and alkaline phosphatase from chick liver, intestine and heart is demonstrated by polyacrilamide disc gel electrophoresis. Liver and heart show the same number of molecular forms of acid and alkaline phosphatases. In contrast, the intestine homogenate shows electrophoretic bands different in number and in gel position from those of the liver and of the heart.