hemoglobin S

n.
  1. An abnormal hemoglobin in which valine has replaced glutamic acid causing the hemoglobin to become less soluble under decreasing oxygen concentrations and to polymerize into crystals that distort the red blood cells into a sickle shape.sickle cell hemoglobin
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.