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Escherichia coli strains with mutations in 3 genes coding for redox functions--torA, nuoM and glpC--are able to grow with pyruvate as carbon source, but are not able to use a combination of serine, glycine and leucine as carbon source, unlike the parent strain which uses either. All three mutants are able to produce and activate L-serine deaminase (L-SD) when grown in glucose minimal medium, and thus should be able to convert serine to pyruvate and grow on it. We suggest that activation of L-SD involves specific chemical reactions, perhaps building an Fe-S cluster. Mutant cells can carry out the necessary reaction to activate L-SD when grown in glucose minimal medium but apparently cannot do so when grown in SGL medium.

Single crystals of D-serine dehydratase from Escherichia coli complexed with 3-amino-2-hydroxypropionate have been obtained from ammonium sulfate solution (pH 7.0) by vapor diffusion. The crystals belong to the trigonal space group P3(1) or P3(2) with a = b = 81.3 A and c = 58.4 A. The asymmetric unit cell contains one protein molecule with Mr = 48,289. The crystals diffract to at least 3.0 A resolution and are suitable for X-ray structure analysis.

The enzymatic methods for plasma pyridoxal 5'-phosphate (PLP) assay using L-tyrosine apodecarboxylase (apo-LTD) and D-serine apodehydratase (apo-DSD) were compared with respect to their operating characteristics, accuracy and precision. With the apo-LTD assay, the recovery of authentic PLP added to irradiated plasma was 96-100% and the precision for within-run and run-to-run replicates was 4-5% (coefficient of variation). The recovery of authentic PLP with the apo-DSD assay tended to be lower (viz., 95%) and the within-run and run-to-run coefficients of variation tended to be higher (viz., 5-6%), but these differences were not statistically significant. When these two assay methods were directly compared in determining the plasma PLP levels of 67 hospitalized patients, the regression lines exhibited correlation coefficients of 0.89 and 0.92 and slopes of 0.77 and 0.78, respectively. When the plasma PLP values were less than 7.5 ng/ml, the values determined by the apo-DSD assay tended to be higher than those measured by the apo-LTD method and vice versa. The lack of better agreement between the two assay methods may be explained by the fact that an inhibitor exists in plasma extracts that impairs the binding of PLP to apo-DSD and that the correction for this interference may not be uniform from one plasma sample to another. However, if one is willing to tolerate the small discrepancies between the values obtained by the apo-DSD and apo-LTD assays, these assay methods can be used interchangeably. The apo-DSD assay has the advantage of being easily adapted to a modern automated spectrophotometric centrifugal analyzer.