most abundant protein

[nsaunders at molbiol.ox.ac.uk]

I've was told in a lecture some time ago that RuBisCo was the most abundant 
protein on earth. I guess the justification is that because energy is lost as 
you move up the food chain, there has to be more vegetable protein than animal 
protein and RuBisCo is synthesized in large amounts, not only in higher plants 
but many lower plants and CO2-fixing microorganisms too, so is likely to be 
the most abundant protein. But I don't know how good an estimate this is; I'd 
have thought it was necessary to show that it was one of, if not the major 
protein on a per-cell basis in many different organisms.

The largest known protein in 1992 was a sarcomeric protein called titin (I 
just pulled this off Medline, the ref. is Labeit et. al.(1992), EMBO 
J.11:1711-1716. Apparently individual molecules are over 1 micron in length. 
They had sequenced 30 000 bp of DNA (1000kDa of protein), but imply this isn't 
the whole thing. As far as I know this is still the biggest.

Neil Saunders,
Dept. Of Biochemistry,
Oxford

nsaunders at molbiol.ox.ac.uk