Wednesday, December 06, 2006

What is the most abundant protein in humans? ...on earth?

Today at lunch we had a heated discussion on what is the most abundent protein in humans (by mass?). We speculated that it would be a member of the cytoskeleton (actin, keratin), or part of blood (albumin, hemoglobin), an extracellular matrix/bone component (collagen), a mithochondrial enzyme (GAPDH), a very small abundant protein (ubiquitin), or a component of chromatin (histones). We each picked one and made a bet to what google would tell us. Well after a bit of searching here is what I find. From google answers: "I have found definite statements that collagen is the most abundant, followed by actin. I have found claims that osteocalcin takes the 7th place, and SOD the 5th. Albumin, myosin, keratin and the globulins are also strong contenders for places in the top 10."
There is of course differences when you compare moles and mass, as proteins like collagen are massive (>1000AA) compared to something like ubiquitin (<100AA). But looking at mass we can guess something like this...
  1. Collagen (25% of proteins)
  2. Actin (20% of dry muscle mass)
  3. Myosin? (second most abundent in muscle) or keratin (most abundent in epithelium/hair)?
  4. Albumin? (60% of serum protein,and only 40% of all albumin is present in serum)
  5. Superoxyde dismutase (most abundent in mitochondria)
  6. Hemoglobin? (95% of RBC dry mass)
  7. Osteocalcin (second most abundent in bones after collagen)
But which protein is most abundant on earth? Well it turns out it could be rubisco, the photosynthesis enzyme (30-50% of soluable chloroplast protein), found in plants, algea and plancton...
However, I have not given up on the idea that it should be a bacterial protein considering they have so much biomass, all to way to 2km down the crust and at the bottom of oceans. I would quote Stephen J Gould for this matter : "When one considers how deeply entrenched has been the dogma that most earthly biomass lies in the wood of our trees, this potentially greater weight of underground bacteria represents a major revision of conventional biology and quite a boost for the modal bacter. Not only does the Earth contain more bacterial organisms than all others combined (scarcely surprising, given their minimal size and mass); not only do bacteria live in more places and work in a greater variety of metabolic ways; not only did bacteria alone constitute the first half of life's history, with no slackening in diversity thereafter; but also, and most surprisingly, total bacterial biomass (even at such minimal weight per cell) may exceed all the rest of life combined, even forest trees, once we include the subterranean populations as well."


11 comments:

Bayman said...

Give me a break. Everyone knows Stephen J Gould is full of it, as I clearly demonstrated by kicking his ass in the Darwin Wars...The real question is which gene is the most abundant on the Earth...

Richard Dawkins said...

Bayman you plagaristic bastard, I was the one who kicked Stephen J Gould's ass, and I'm the one who wrote the selfish gene...Expect a phone call...my Oxford lawyers will be all over your ass.

Ben said...

Hmm, I'm surprised titin wasn't in there, especially if you're going by weight. It's not terribly abundant, but it's the largest known, and it's full name is the longest word in the English language, making it that much cooler at any rate.

Anonymous Coward said...

“Titin, also called connectin, is the largest protein known and is the
third most abundant protein in striated muscle behind only myosin and
actin”

Anonymous Coward said...

Oh man best scientist name ever... Bang et al. (2001) determined that the complete sequence of human titin encodes a 38,138-amino acid protein with a molecular mass of 4,200 kD.

kamel said...

I still think we should be measuring by number not mass! If I have 20 grapes and 3 grapefruits nobody is going to say the grapefruit is more abundant. Histones FTW!

Anonymous Coward said...

while histones are smallish, as an octamer it gets to be quite large >100KDa. However a histone supposedly wins the record for the smallest protein-coding gene, mostly because it has no intron (~500bp). If you're looking for the smallest protein there are 54 predicted to be <100AA in the human genome. With the smallest ranking in at 54AA. If you take post-translational modeifications into account, then there are several hormonal peptide that are smaller...

Anonymous said...

I saw you talking about ubiquitin protein, so I thought you might be interested in Science Magazine's current webinar regarding disease treatment:
Science Magazine's Webinar: The Ubiquitin-Proteasome Pathway

Anonymous said...

Rubisco is the most abundant protein on earth. It is not found in humans because it relates to photosynthesis which only occurs in plants, but it is an enzyme (which are made of proteins).

Baculovirus Protein Expression said...

Hi Friends,

The single most abundant protein in the human body is Collagen. It is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in bone, blood vessels, and intervertebral disc. Thanks a lot...

Acls certification said...

Hello,

The most abundant protein in the body is collagen. It makes up about ninety-percent of connective tissue. It is a major component in many tissues, especially bone, muscles, skin, blood vessels, and even the cornea of the eye. Thanks a lot for sharing with us...