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The ancestral solution to oxygen transport is with hemoglobin (or, similar proteins) dissolved in blood (or, "hemolymph", but, basically, dissolved in water. ) What was the advantage of enclosing the oxygen-transport proteins in cells?

Pikachu
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  • Hello, looks like this is your first question. Please notice that although I got your point and I think your question is good, you should do your own researches before posting here: this will not only improve the general quality of this SE, but will also make other expert users eager to answer, while short questions without references usually get no answer.Welcome to Biology SE by the way :) – francesco Apr 07 '20 at 06:43
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    Does this answer your question? Why isn’t Haemoglobin a plasma protein, rather than being encompassed by the erythrocyte? – David Apr 07 '20 at 08:38
  • @David what do you think yourself? – Pikachu Apr 07 '20 at 08:43
  • My angle is that, if you know, with certainty, the answer, then I'd like to hear it. If you just scan for something that "might" answer the question, you are no better than a search engine. If you know for a fact that a url you shared does answer it, then, good. In your opinion, does that url answer the question? Tumbisapichu suggested concentration as main factor. Sounds plausible. I've thought myself that oxidative stress might be it, ROS is in proportion to oxygen pressure, and I'd assume it is highest inside the oxygen transport cells, that also lack mitochondria (the main source for ROS) – Pikachu Apr 07 '20 at 09:17
  • The “does this answer your question” is the new and misleading auto-generated text when you flag a question as a duplicate. The point is not whether it answers your question, but that duplicate or similar questions are closed. I have no particular interest in the topic I just remember it coming up previously. – David Apr 07 '20 at 10:00
  • Well you flagged it as duplicate, so, you claim that it does answer the question. That the comment is auto-generated does not change that. Does it answer the question, in your opinion? What was the evolutionary advantage of enclosing hemoglobin in cells? – Pikachu Apr 07 '20 at 10:46

2 Answers2

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If you enclose the globin in a cell you can achieve a high concentration of the globin, which makes for a faster, readily usable pool available, and it is not subject to degradation (via proteases, or other mechanisms) as if it was just dissolved. In addition, all other functions of the globins (pH regulation, CO2 metabolism, etc) will be more tightly controlled if the globin is on the same site (i.e., inside a cell), instead of being mixed in a milieu. All of that has probably more to do with the evolution of the entire circulatory system, as a whole, and only sequentially as the 'enclosure' of globins in specialized cells. You can find some more details here.

TumbiSapichu
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  • If a higher concentration is the main benefit, is the primarily factor viscosity, that enclosed cells can have higher concentration without decreasing viscosity of the blood? – Pikachu Apr 07 '20 at 06:50
  • That's also a good point, but more than viscosity I'd say that a factor would me osmolarity. Dissolved proteins in a circulatory system make for higher osmotic pressure, which would need to be compensated. – TumbiSapichu Apr 07 '20 at 06:53
  • Good point. My own analysis is that the cells then prevent endosmosis by tension in the cytoskeleton matrix. (I'd guess a way to compensate for the osmolarity is necessary, otherwise the cell would be in the same situation as a hyperosmotic blood. ) – Pikachu Apr 07 '20 at 06:58
  • What is the scale of concentration increase, roughly? 10-fold? (albumin is 1/10th globin in red blood cells, guessed from that if osmolarity is main factor) – Pikachu Apr 07 '20 at 07:02
  • This might be informative: https://en.wikipedia.org/wiki/Mean_corpuscular_hemoglobin_concentration – TumbiSapichu Apr 07 '20 at 07:12
  • have seen that, easily attainable. and albumin concentration is roughly 1/10th of MCHC – Pikachu Apr 07 '20 at 07:15
  • the hemocyanin concentration (or whatever pre-blood cell animals tend to use) is what it harder to find. if osmolarity was the main factor, I was guessing albumin could be a good estimate, that it is 1/10th of the MCHC. since roughly 50% of blood volume is red blood cells, concentration increase as advantage driving evolution of blood cells would be half of that, 5x. just guessing. do you know the scale of concentration increase? – Pikachu Apr 07 '20 at 07:17
  • Hmm, no I don't know. – TumbiSapichu Apr 07 '20 at 07:21
  • here it looks like it is 9 g/L, 1/4th of that of erythrocytes. https://www.sciencedirect.com/science/article/abs/pii/0014489472901117. with 50% red blood cells in blood, that means concentration is only doubled. – Pikachu Apr 07 '20 at 07:31
  • my intuition was that blood cells protect against oxidative stress, primarily, by moving oxygen into the cell. they also die pretty quickly... that as endothermy evolved etc, and metabolic rates and oxygen consumption increased, it was necessary. – Pikachu Apr 07 '20 at 07:32
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Also, hiding the Iron from invading bacteria is good. Free iron is a limiting factor for bacterial growth.

Polypipe Wrangler
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