The Structural Properties of Spinach Leaf Glyoxylic Acid Reductase

A homogeneous form of spinach leaf glyoxylic acid reductase has been isolated from commercial crystalline preparations. The enzyme catalyzes the reduction of hydroxypyruvate as well as glyoxylate and has a molecular weight of 97,500 ± 5,000. It is composed of two equal-sized subunits which are dissociated by exposure to 6.0 m guanidine hydrochloride-0.1 m mercaptoethanol, 8.0 m urea-0.1 m mercaptoethanol, or iodoacetate. Analytical disc gel analyses, amino-terminal end group analyses, and peptide mapping indicate that the polypeptide chains of each subunit are similar in their primary structure. The subunits can reassociate to yield the native enzyme and a nearly inactive tetramer. Several additional forms of the enzyme have been shown and characterized. Two of these have the same molecular weight as the above enzyme and a similar amino acid composition; another exhibits a lower molecular weight (83,000 ± 5,000) and a different amino acid content. They can be distinguished from this enzyme by their isoelectric points, stabilities, specific activities, and spectra, yet are also composed of two equal-sized subunits with similar properties of dissociation and reassociation. The lower molecular weight protein is presumed to be a degraded form of the spinach enzyme.