Variation in Casein from Individual Human Milk Samples

d-Glucose dehydrogenase purified from the membrane of Pseudomonas fluorescens was shown to be highly hydrophobic in amino acid analysis, with a polarity of 39.7%. The purified enzyme was inactivated upon removal of detergent by acetone treatment. The detergent-depleted enzyme was activated partially with Triton X-100, and the activity was restored almost completely upon addition of both phospholipids and Triton X-100, followed by sonication. The purified enzyme, in spite of being a single polypeptide dehydrogenase, directly reduced not only short-chain ubiquinone but also long-chain homologs. It should be noted that coenzyme Q-6 or Q-9 incorporated in phospholipid vesicles was efficiently reduced with the enzyme. These results show that, in the cytoplasmic membrane of Pseudomonas fluorescens, the glucose dehydrogenase may be linked to an electron transport chain via ubiquinone.