Protein involved in the degradation of thiamine, a water-soluble vitamin which is a member of the vitamin B complex. It occurs in cells largely as its active coenzyme form thiamine pyrophosphate, formerly called cocarboxylase. Thiamine is necessary in the diet of most vertebrates and some microorganisms. Its deficiency causes beriberi in man and polyneuritis in birds. Thiamine pyrophosphate serves as a coenzyme in aldehyde-group transfers.