Blood-group determinants biosynthesis

Fig. 9. Proposed composite structure showing the relationship of the A, B, H, Le , and Le antigenic determinants of the water-soluble human blood group substances from ovarian cysts. The structure of the side chain in brackets has not been established, but the existence of such a chain is indicated by the mechanism of alkaline borohydride degradation and the oligosaccharides isolated. The carbohydrate chain shown is one of many linked to the serines and threonines of the polypeptide backbone. Chains are not homogeneous and may be of various lengths depending upon genetic composition, incomplete biosynthesis, and unknown factors. From Pereira and Kabat, modified from Lloyd and Kabat cf. Kabat. ...

The porphyrin system is a complicated structure consisting of four pyrrole rings connected by methine groups (=CH—). It is the basis of the red blood pigment, the green leaf pigment, and of the cytochromes (redox enzymes). Efforts to determine its chemical structure occupied many decades (KQster, H. Fischer), and finally were crowned by the synthesis of the porphyrin molecule (H. Fischer). We will not follow the tortuous route of the research chemist here, but instead will construct the ring system from simple components, just as the cell does. Thus the biosynthesis will be discussed at the same time. 

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