Pyruvic decarboxylase and acetoin formation in Athiorhodaceae.

Abstract

Studies with cell-free extracts of Rhodopseudomonas palustris strain Q showed that under anaerobic conditions pyruvate was decarboxylated with the stoichiometric formation of carbon dioxide. Other products of the reaction include acetaldehyde and acetoin (acetyl methyl carbinol), indicating the presence of pyruvic decarboxylase. A survey of purple non-sulfur bacteria demonstrated that pyruvic decarboxylase was also formed by R. gelatinosa and R. capsulata and Rhodospirillum molischianum but not by R. rubrum and R. spheroides and Rhodomicrobium vannielii. The enzyme had an optimum pH of 6.25 and an apparent Km of 1.22 × 10−2 M in potassium phosphate buffer (50 mM) at 30C. Pyruvic decarboxylase in photosynthetic bacteria required only thiamine pyrophosphate as a cofactor and it differed in this respect from the enzyme in yeast and in other bacteria which required divalent metal ions as well. Acetoin formation in the Athiorhodaceae, like that in yeast but unlike that in most bacterial species, involved the formation of acetaldehyde from pyruvate.