Biochemical systems involving 'single carbon' transfers.

Known information of l-earbon transfer reactions and the involvement of PGA and vitamin
B12 in these transfers can be summed up as follows:
1. In the synthesis of several protoplasmic constituents, one of the basic building units
has been recognized as the l-carbon unit, expressed as 'methyl', 'hydroxymethyl' and 'formyl',
depending on the oxidation level.
2. These units are known to be derived from simple carbon compounds including formate,
formaldehyde, serine, glycine, acetone, methanol, etc.
3. Reactions involving the transfer of 'hydroxymethyl' or 'formyl' have been characterized
as requiring THPGA as a carrier.
4. Although vitamin B12 shows a potentiating influence, its exact significance in the
l-carbon metabolism is still far from clear.
Diverse other metabolic processes directly or indirectly influenced by the two vitamins
and involving l-C transfers are as yet not precisely defined.
Information regarding changes in oxidation level of the l-carbon unit, and its ultimate
liberation as carbon dioxide, is also meagre. The tempo of recent research, directed in many
ways, is however certain to unfold these patterns ere long.