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My book NCERT(Class 12, Surface chemistry) claims that hemoglobin is a positively charged sol.

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The cytosolic pH in human cells is around 7.4, but fluctuates through the cell cycle

according to this article the isoelectric point of Hemoglobin behaves as follows:

The more nearly free a preparation of hemoglobin is from nonhemoglobin protein the more nearly does the isoelectric point approach 6.8,

So if the isoelectric point is 6.8 for Hemoglobin and pH of cytoplasm is 7.4 so wouldn't be Hemoglobin a negatively charged sol?

As we know in blood, proteins exist as negatively charged species so blood is termed as negatively charged sol, so is there a point I am missing?

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  • $\begingroup$ This may be more appropriate for chemistry.stackexchange.com. $\endgroup$
    – Maximilian Press
    Sep 4, 2021 at 20:15
  • $\begingroup$ @MaximilianPress protein structure of membranes is determining the charge here, as biology is more concerned with things like protein structure, I thought it might be better to post here $\endgroup$
    – Samardeep singh
    Sep 4, 2021 at 20:25
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    $\begingroup$ It's a bit of a value judgment. For the record, I would suggest looking into the different forms of Hb (oxy, deoxy, carboxy) and their ternary structure as oxygenation reduction status etc. should play a role. I am not a chemist but there are a variety of publications in chemistry journals investigating isoelectric behavior of these different forms: sciencedirect.com/science/article/pii/S0021925818745547/…, jbc.org/article/S0021-9258(18)61920-9/pdf, pubmed.ncbi.nlm.nih.gov/7324711 $\endgroup$
    – Maximilian Press
    Sep 4, 2021 at 21:03

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There is a major problem with the item list, hemoglobin is not the same as "blood". In blood, hemoglobin is contained with RBCs and not floating everywhere. Let me show how this can cause a HUGE difference:

  1. Whether hemoglobin is negatively or positively charged will not affect the blood; because it is contained with RBCs whose membrane is negatively charged and doesn't depend to a large degree on its contents. However, blood is actually negatively charged and the main contributor to this is Heparin (negatively charged anticoagulant protein), the RBCs membrane is negatively charged preventing adhesion to themselves and negatively charged membranes of other cells (anti-coagulation mechanism)
  2. intracellular pH of RBCs is around 7.1 (1). the isoelectric point of haemoglobin is a bit of trouble to agree on because actually the alpha chain of hemoglobin has isoelectric point of (7.5–7.8) while beta subunit is (6.1–6.7) (2). I didn't find a source assessing the in-vivo charge of hemoglobin or electrophoresis at physiological pH, even though if electrophoresis at physiological pH is present, it won't be a good indicator because isoelectric point can vary in-vivo as there are many acids other than H+. I would like to quote the following paragraph from National Academy of Sciences (US) and National Research Council (US) Division of Medical Sciences. Conference on Hemoglobin (3):

Near the physiological pH probably all of the charges on hemoglobins come from their constituent amino acids. Neutral amino acids contribute one terminal carboxyl and one terminal amino group to each polypeptide chain which is not a ring. Additional positive charges are contributed by the nitrogenous groups of the three basic amino acids, Rb. Additional negative charges are contributed by the second carboxyl group of aspartic and glutamic acids, Ra

pH at which several amino acid in Hemoglobin ionize:

enter image description here

References :

  1. Swietach, P., Tiffert, T., Mauritz, J. M., Seear, R., Esposito, A., Kaminski, C. F., Lew, V. L., & Vaughan-Jones, R. D. (2010). Hydrogen ion dynamics in human red blood cells. The Journal of physiology, 588(Pt 24), 4995–5014. https://doi.org/10.1113/jphysiol.2010.197392
  2. Devineau, S., Inoue, K. I., Kusaka, R., Urashima, S. H., Nihonyanagi, S., Baigl, D., ... & Tahara, T. (2017). Change of the isoelectric point of hemoglobin at the air/water interface probed by the orientational flip-flop of water molecules. Physical Chemistry Chemical Physics, 19(16), 10292-10300.
  3. National Academy of Sciences (US) and National Research Council (US) Division of Medical Sciences. Conference on Hemoglobin: 2–3 May 1957. Washington (DC): National Academies Press (US); 1958. THE STRUCTURAL BASIS OF DIFFERENCES IN ELECTROPHORETIC BEHAVIOR OF HUMAN HEMOGLOBINS. Available from: https://www.ncbi.nlm.nih.gov/books/NBK224284/
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    $\begingroup$ Ok ,then can you explain then if the isoelectric point of haemoglobin in 6.8 , how can it have a net positive charge at physiological ph of cytoplasm of 7.2, Is the data of isoelectric point for Haemoglobin incorrect? $\endgroup$
    – Samardeep singh
    Sep 6, 2021 at 21:07
  • $\begingroup$ @Samardeepsingh, I edited the answer $\endgroup$
    – mohamed
    Sep 7, 2021 at 9:00

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