Heme Synthesis by Cultured Human Marrow Cells in Response to Cyanate-treated Erythropoietin 1

Abstract

Sickle cell disease (homozygous hemoglobin S) results from the presence of an abnormal hemoglobin (β6 val →glu) in the red blood cells (1) which, upon deoxy-genation, causes the erythrocytes to sickle. Cerami and Manning (2) have demonstrated that treatment in vitro with potassium cyanate (KCNO) can prevent the sickling of erythrocytes obtained from patients with sickle cell disease. Moreover, sickle cell erythrocytes which have been treated in vitro with cyanate exhibit an increase in their mean 50% survival time, as measured by radiochromium, when they are returned to the patient (3). Although cyanate may result in the carbamylation of the ∊-amino groups of lysine residues in proteins (4), there was no detectable carbamylation of the lysine residues of hemoglobin S in these studies. Thus, these actions of cyanate appear to be mediated by the specific carbamylation of the amino terminal valine residues of the hemoglobin S molecule. More recently, Manning et al. (5) have noted that hemoglobin is car-bamylated by injected ¹⁴C-cyanate to a much greater extent than the serum proteins. This specificity has been attributed to the low pKa of the amino terminal residues of oxyhemoglobin.

Cyanate has the potential, however, to modify the free amino groups of many proteins, since the carbamylation of these groups is irreversible and nonspecific (6).

In this regard, deFuria et al. (7) have demonstrated a decrease (approximately 25%) in the activity of the enzyme pyruvate kinase in sickle cells treated with cyanate. Additionally, Crist et al. (8) have reported that intravenously administered cyanate results in the carbamylation of brain, blood, and liver proteins. Sodium cyanate in vitro (10 mM) has also been reported to adversely affect the activity of bovine lutein-izing hormone and thyroid stimulating hormone as determined by bioassay (9).