Scanning transmission electron microscopy of extracellular annelid hemoglobins

Abstract

Micrographs of negatively stained extracellular hemoglobins of Lumbricus terrestris and Arenicola marina obtained with the scanning transmission electron microscope show that their appearance is consistent with a model of two hexagonal tiers of pentagonally shaped subunits. The dimensions are similar: a vertex-to-vertex diameter of 300±8 A ̊ and a height of 200±11 A ̊ . The diameter of each subunit is about 110 Å. These dimensions are markedly larger than those reported previously by other investigators. However, these values are similar to those recently obtained by X-ray diffraction of wet crystals of Lumbricus hemoglobin.