Respiratory Pigments Related to Tissues

Discussion in 'Physiology and Biology' started by Fujisawas Sake, Jun 22, 2008.

  1. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    At a talk on a local species of Chitin last year, a graduate student mentioned that the species (name escapes me at the moment) used hemoglobin in its foot. Naturally, I and my invert zoo instructor woke up from our boredom induced haze and started asking questions, which puzzled siad graduate student.

    So how many respiratory pigments are found in Cephalopods and how are they distributed among tissues?
     
  2. monty

    monty Colossal Squid Staff Member Supporter

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    chitin->chiton, unless I'm mistaken, right?

    I believe all cephs use haemocyanin (as spelled in many different ways.) Taollan dropped some interesting hints about ceph haemocyanin in email, but I'm not sure if I'm supposed to mention them. He also knows this stuff a lot better than I do, so I hope he responds here...
     
  3. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Slight Hi-Jack

    Well, maybe a hi, Monty - just noticed your official new status!
     
  4. monty

    monty Colossal Squid Staff Member Supporter

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    thanks. I'm still learning the ropes on how to use my new powers.
     
  5. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Wow, that was a freudian slip of sorts... Thanks! I think the species discussed was Kimbrella
     
  6. monty

    monty Colossal Squid Staff Member Supporter

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    sometimes a mollusc is just a mollusc.
     
  7. Taollan

    Taollan Vampyroteuthis Supporter

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    Kimberella is a pre-cambrian animal that many think is one of the earliest mollusks. (http://adsabs.harvard.edu/abs/1997Natur.388..868F). It is actually kinda looks like a shell-less chiton.
    I think the chiton you are thinking of is Lepidochiton rugatus (http://cat.inist.fr/?aModele=afficheN&cpsidt=7718379, http://jeb.biologists.org/cgi/reprint/201/8/1085 has a good discussion and even a picture!!). This chiton has extracellular hemoglobins in various tissues, but has a circulating hemocyanin. Other mollusks that use hemocyanin included Planorbid snails (which are also vectors for Chytrid fungus, but that is neither here nor there). Notably nearly all hydrothermal vent and cold seep organisms (including bivalves such as Calyptogena and Solemya) use some forms of circulating hemoglobin to transport hydrogen sulfide (H2S) to their symbiotic bacteria that metabolize it. H2S is very toxic to us because it bind to our hemoglobin much more readily than oxygen (on a seperate adaptive note, for this reason we have evolved the ability to detect very small doses of H2S with our noses, which is what makes flatulence and rotten eggs so off-putting). Anyhow, these vent and seep animals use this property of hemoglobin to transport H2S.
    But onto the meat of the questions. I don't know of any cephs that have any hemoglobin. But to tell you the truth, cephs have refined their hemocyanin to the point that a switch to hemoglobin would actually be a step backwards in terms of performance. One of the "unique characteristics" of vertebrate hemoglobin like ours is its cooperativity. We have four subunits in each of our hemoglobin, each of which can bind an oxygen. After the first subunit binds an oxygen, interaction with the other subunits causes the second to bind its oxygen more readily. Subsequently the thirds binds an oxygen more readily than the second and the fourth more than the third. This is on of the primary mechanism that makes vertebrate hemoglobin so efficient at transporting oxygen. Hemocyanins generally don't display cooperative binding of oxygen, but ceph hemocyanin DOES!!!, making it, atleast in terms of performace closer to vertebrate hemoglobins. Ceph hemocyanins also have a very large Bohr effect. The Bohr effect is an property in which a respiratory pigment will bind oxygen less tightly in the presence of CO2. This means that when a hemoglobin or hemocyanin gets to a peripheral tissue, where CO2 is high because of cellular respiration, the bohr effect will cause the pigment to unload it oxygen. So ceph hemocyanin, having a large bohr effect (much larger than even vertebrate hemoglobin), can be very efficient at delivering oxygen to tissues.
    These two effect together help to make ceph hemocyanin very efficient carriers of oxygen at low O2 levels, much better than hemoglobin. This is partly why Humboldt squid can zoom around in the oxygen minimum layer without seeming to slow down much. Octopuses can maintain a steady uptake of Oxygen down to very low pressures, much lower than you or I can.
    Well, all of that is to say that for cephs, the use of hemoglobin would probably be detrimental to what they have now...
     
  8. Taollan

    Taollan Vampyroteuthis Supporter

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    OK, so I just ready your original question again. Short answer: Cephs, as far as I know (which I am 99.49% sure), have one respiratory pigment: hemocyanin (which is kinda misleading because hemocyanin is a class of respiratory pigments, not just 1).
    In octopuses individual hemocyanin molecules have six or seven subunits (labeled A B C D E F G), each subunit able to bind one O2 molecule. These individual molecules form a larger structure consisting of ten (so a total of 60 subunits) of the individual hemocyanin molecules, taking the form of a short, fat cylinder, with collars on the ends.
     
  9. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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  10. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Oh, and I was thinking of Katherina, but wrote Kimberella. Just dug out omy old copy of Between Pacific Tides and refreshed my memory...
     
  11. monty

    monty Colossal Squid Staff Member Supporter

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    That inkblot looks like a geoduck. And that one looks like a banana slug.
     

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