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I have done research on blood and in particular the component adding color and transferring oxygen.

Hemocyanin is directly dissolved into the blood. This works for an octopus, but not a reptilian alien. Hemoglobin however is contained inside RBCs and very little is directly dissolved into the blood. This could work for a reptilian alien but it seems too earthlike to me.

So I figured that maybe I could have the Hemocyanin compound inside globin proteins inside cells and these cells would be BBCs or blue blood cells.

Each Hemocyanin has 2 copper ions that can bond with 1 oxygen per ion so per molecule that is 2 oxygen molecules transported, double the capacity of hemoglobin. Other than that it is similar to hemoglobin(each protein has 4 subunits and each subunit has 1 Hemocyanin molecule.

Now, arterial blood with Hemocyanin looks blue because it is blue. Venous blood with Hemocyanin however is colorless. So the only way you could see veins is by seeing the tissue itself and that is pretty much impossible without an incision. So the only blood vessels you would ever see with the naked eye are arteries.

Is cyanoglobin a plausible way to have oxygen transported in a reptilian alien who most likely has a totally different evolutionary tree from ours?

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  • $\begingroup$ I will not be of great help, since my biological knowledge is too limited. But perhaps a way to reach an answer is to define, which properties of reptiles are important to you. Then you can assess, which are already present in Scorpions, Crabs, Spiders and other animals using Hc. $\endgroup$ – Ludi Dec 31 '16 at 9:04
  • $\begingroup$ In other words: since our reptiles will differ from real ones, we need to know which differences are acceptable in your scenario. $\endgroup$ – Ludi Dec 31 '16 at 9:10
  • $\begingroup$ Why does an oxygen transport molecule not bound in a cell "not work" for an alien reptilian? $\endgroup$ – nigel222 Dec 31 '16 at 12:40
  • $\begingroup$ You may already have seen this discussion about an intelligent humanoid alien with hemocyanin in its blood, but it makes some interesting points. giantitp.com/forums/… $\endgroup$ – a4android Dec 31 '16 at 13:58
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    $\begingroup$ I misread the title as cyanogoblin. Now I'm disappointed. $\endgroup$ – Zxyrra Jan 1 '17 at 1:52
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The simple answer is no.

No, it's just too big to fit inside the cells and retain functionality at its lower binding potential. Hb forms tetramers of 64 kDa, while Hc subunits start at 75 kDa and often form massive chains exceeding 1500 kDa, depending on species.

On a molecular chemistry scale, that's flipping massive - for comparison, the largest protein known (titin) is ~3800 kDa.

Source: hemocyanin blood using humanoid alien

Also, hemocyanin (Hc) is limited in its oxygen carrying capacity.

Unit for unit, Hc carries about 25% of the oxygen compared to Hb but achieves saturation at much lower partial pressures of oxygen, so technically it's more efficient at binding oxygen, just less efficient at carrying it.

As I said, a fix would be to have a higher Hc concentration (~4 times to be precise), resulting in very intensely blue blood (oxygenated) or colourless (deoxygenated), much like our blood is bright/dark red, only more extreme.

Reading up on it some more Hc appears to function better at cold temperatures (spiders and scorpions in the Tropics aside), which could be another characteristic of our Hc humanoid (lower body temperature).

Source: ibid

Higher concentration of Hc suggests the fluid blood itself needs to be saturated with Hc, rather like the blood of an octopus only more concentrated.

However, Hc blood does work better at lower oxygen levels than hemoglobin blood. So if your reptilean alien existed in a low oxygen atmosphere, then Hc blood might be an advantage. But, fortunately, cynanoglobin seems to be out. Pity really the idea of blue blooded aliens is rather nice. Another beautiful hypothesis slain by an ugly fact (to paraphrase TH Huxley who called it the tragedy of science).

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  • $\begingroup$ Wait, hemocyanin is less efficient at transporting oxygen? I thought it would be double the efficiency since it has 2 coppers that each can bind to 1 oxygen compared to our 1 iron in hemoglobin $\endgroup$ – Caters Dec 31 '16 at 14:53
  • $\begingroup$ @Caters It's complicated. Hemocyanin is more efficient at picking up oxygen, especially at low oxygen levels, but poor at transporting it around the body. I suggest you plough through the link I gave, it will take time. The information is there in dribs and drabs. $\endgroup$ – a4android Jan 1 '17 at 2:39
  • $\begingroup$ You shouldn’t extrapolate characteristics of existing hemocyanins to an unrelated biology. It's theorized that hemocyanins aggregate into large bodies because they are not contained in cells. It's not an obligatory feature of hemocyanins. Also most hemocyanins evolved in low oxygen environments so they are designed to bind oxygen at low concentrations. An alien hemocyanin that evolved alongside a terrestrial reptile in an alien atmosphere could develop very different characteristics. You can't argue hemocyanins couldn't sustain a reptilian animal merely because this doesn't exist on earth. $\endgroup$ – Mike Nichols Jan 31 '18 at 15:25
  • $\begingroup$ @MikeNichols I was taking a conservative approach to the hemocyanin question. Basically staying with hemocyanin as we know it. Hypothesizing that alien hemocyanins could sustain large animals like reptiles is speculative, uncertain and currently unknowable. Yes it would be easy to say, of course, hemocyanins or some version thereof could work, but nobody knows. Earth-based examples suggest no, but that doesn't prevent more efficient hemocyanin evolving on another planet. Again nobody knows. A SF story could assume it has, & that's fine. $\endgroup$ – a4android Feb 1 '18 at 7:14
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On the other hand, I have some information suggesting that Hc isn't quite as dire as it seems. If O2 concentration and temperature are correct, i.e. what you might find on a near Earth mass exomoon orbiting a giant planet 3-6 times the size of Jupiter, there might be a narrow window where complex life could evolve despite the seeming disadvantages and/or less iron due to depletion in that system forcing evolution down a different path.

Think horseshoe crabs here, a plausible evolutionary tree would be life starting in deep ocean(s) near black smokers and the resultant life forms eventually adapting to climatic change by evolving into land dwellers. Over time pressures similar to on Earth may lead to intelligence and eventually consciousness. I further defined the properties below.

"Blue skin, copper based hemocyanin (i.e. similar to horseshoe crab) and capable of seeing mid infrared to low visible light, 930 to 681nm but otherwise very much like us. 41.17 LY distance, around an M dwarf with three large exoplanets and one Earth-sized exomoon, 1.22G units.

Height: a little under 0.9 metres, bilateral symmetry and capable of limited photo-mimetic abilities."

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    $\begingroup$ Did you came with the properties on your own, or did you find them somewhere without referencing your sources? Also, I assume 41.17 LY distance and blue skin are properties of different things, right? $\endgroup$ – L.Dutch Jan 31 '18 at 5:40
  • $\begingroup$ Welcome to the site. If you could either identify that these are your own ruminations or link to the source you used, the community would appreciate it. In the former case, it is preferable to explain how and why such qualities are viable. You may do this with an edit. Feel free to take the tour to get a better understanding of the site. $\endgroup$ – Frostfyre Jan 31 '18 at 5:57
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    $\begingroup$ @Frostfyre - no one ever welcomed me :( $\endgroup$ – ArtisticPhoenix Jan 31 '18 at 6:32
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    $\begingroup$ @ArtisticPhoenix probably because your posts did not land in low-quality review queue and you never looked like new guy. Is this really a bad thing? $\endgroup$ – Mołot Jan 31 '18 at 13:14
  • $\begingroup$ @Frostfyre - I suppose not, probably because I have like 9k on SO $\endgroup$ – ArtisticPhoenix Jan 31 '18 at 17:19

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