Molecular diversity of glucose-6-phosphate dehydrogenase: rat enzyme structure identifies NH2-terminal segment, shows initiation from sites nonequivalent in different organisms, and establishes otherwise extensive sequence conservation

Molecular characterization of the Escherichia coli K-12 zwf gene encoding glucose 6-phosphate dehydrogenase

In Escherichia coli K-12, expression of zwf, the gene for glucose 6-phosphate dehydrogenase, is coordinated with the cellular growth rate and induced by superoxide-generating agents. To initiate the study of the molecular mechanisms regulating its expression, the gene was cloned and its DNA sequence was determined. The 5' ends of zwf mRNA isolated from cells growing in glucose and acetate minimal media were mapped. The map was complex in that transcripts mapped to -45, -52, and -62, with respect to the beginning of the coding sequence. Three analytical methods were used to search the DNA sequence for putative promoters. Only one sequence for a promoter recognized by the sigma 70 form of RNA polymerase was found by all three search routines that could be aligned with a mapped transcript, indicating that the other transcripts arise by processing of the mRNA. A computer-assisted search did not reveal a thermodynamically stable long-range mRNA secondary structure that is capable of sequestering the translation initiation region, which suggests that growth-rate-dependent regulation of glucose 6-phosphate dehydrogenase level may not be carried out by a mechanism similar to the one for the gene (gnd) for 6-phosphogluconate dehydrogenase. The DNA segment between the -10 hexamer and the start point of transcription resembles the discriminator sequence of stable RNA genes, which has been implicated in stringent control and growth-rate-dependent regulation.

Screening method for large numbers of dye-adsorbents for enzyme purification

A method is described by means of which 96 different dye-adsorbents can be tested simultaneously for their ability to bind enzymes and to test their biospecific elution. Small amounts of cell-free extract are applied to dye-adsorbents which are packed in a 96-well transplate cartridge. After biospecific elution, the amount of the eluted enzyme is tested in a microtitre plate assay. The method is illustrated by the purification of glycerol dehydrogenase (E.C. 1.1.1.72), 6-phosphogluconate dehydrogenase (E.C. 1.1.1.44) and glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) from the hyphal fungus Aspergillus nidulans.

Glucose-6-phosphate dehydrogenase. Characteristics revealed by the rat liver enzyme structure

The primary structure of glucose-6-phosphate dehydrogenase from rat liver has been determined, showing the mature polypeptide to consist of 513 amino acid residues, with an acyl-blocked N-terminus. This structure is homologous to those of both other eutherian and marsupial mammals (human and opossum), thus characterizing a mammalian type enzyme to which the human form, notwithstanding its large number of genetic variants, conforms. The mammalian type differs from the fruit fly enzyme by about 50%. Known mutant forms exhibit further differences, widely distributed along the polypeptide chain. Structural patterns show glucose-6-phosphate dehydrogenases to consist of a few variable regions intermixed with relatively constant segments.