The amino acid sequence of soybean leghaemoglobin c2

Abstract

1. Introduction The leghaemoglobin found in the root nodules of the soybean plant (G&&e max cultivar Lincoln) after rhizobial infection was originally fractionated into two major and two minor components [ 1,2]. Recently, the second of the major components, leghaemoglobin c, has been found to consist of two distinct molecular species, leghaemoglobin cl and c2, separable by elution from a DEAE cellulose column using a continuous acetate gradient at pH 5.2 [3]. Since the amino acid sequence of the first major component, leghaemoglobin a, is known [4] and it has been well characterized both structurally, and functionally [S-8] we felt it would be of value to elucidate the primary structure of a second major component, leghaemoglobin c2, as a step towards establishing a function (if any) for the multiplicity of leghaemoglobin species found in the root nodules of most legumes. 2. Materials and methods Soybean plants were grown as previously described [9] and isolated by gradient elution (10 to 50 mM acetate) at pH 5.2 from a DEAE cellulose column [3]. The leghaemoglobin c2 fraction was pooled and rechro- matographed on a shallow gradient (25-35 mM acetate) to ensure removal of the cl component. The protein (65 mg) was dehaemed by the HCl-acetone method [lo] and succinylated in an auto-pH titrator at pH 9.2 by the addition of eight lots of