Hemoglobin is present in :

Hemoglobin, a tetrameric protein of erythrocytes, transpos O2 to the tissues and returns CO2 and protons to the lungs. The heme in haemoglobin is surrounded by a hydrophobic pocket, which is necessary in order for it to bind oxygen reversibly without undergoing oxidation or other undesirable reactions. Ref: Kennelly P.J., Rodwell V.W. (2011). Chapter 6. Proteins: Myoglobin & Hemoglobin. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.