Analysis of maize and its close relative teosinte reveals that there are, at least, 28 allozymes of the b-glucosidase isozyme Glu1. Of these 28 allozymes, only 8 were found in the common maize inbreds when studies comprising 406 (C.W. Stuber and M.M. Goodman, MNL 56:127-132, 1982) and 363 lines (Kahler et al., MNL 58:32-38, 1984) were conducted. We investigated the two commonly found Glu1 allozymes, Glu1-1 and Glu1-7 at the nucleotide and amino acid sequence levels, in order to determine the molecular basis of electrophoretic mobility differences between these allozymes in native gels.

The comparison of the two allozymes at the protein level reveals that they differ with respect to 2 amino acid substitutions: N vs. K at position 107 and D vs. A at position 423 (Figure 1). Proteins move in a native gel primarily according to their net charge if the pore size in the gel is not restrictive. Thus allozyme Glu1-1 (OH7B) moves faster than allozyme Glu1-7 (K55) in an alkaline native gel because the former has two additional negative charges due to the loss of a K and gain of a D in compensation to the latter. However, there are 12 different allozymes between these Glu1-1 and Glu1-7 allozymes that can be distinguished based on their electrophoretic mobility. This suggests that the charge difference may not fully explain the electrophoretic mobility differences among the Glu1 allozymes. Some of the mobility differences may result from changes in solvent accessibility and pK of the ionizable groups or compactness of the native structure depending upon the positions of both charged and noncharged amino acids.

Figure 1. Alignment of the mature proteins of Glu1-1 and Glu1-7 allozymes at the amino acid sequence level. The difference between the two protein sequences involves 2 amino acid substitutions; N to K at position 107 and D to A at position 423.

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