Purification and properties of soluble and bound γ- glutamyltransferases from radish cotyledon

Abstract

Soluble and cell wall bound γ-glutamyltransferases (GGTs) were purified from radish (Raphanus sativus L.) cotyledons. Soluble GGTs (GGT I and II) had the same Mr of 63,000, and were composed of a heavy subunit (Mr, 42,000) and a light one (Mr, 21,000). The properties of GGT I and II were similar. Bound GGTs (GGT A and B) were purified to homogeneity from the pellet after the extraction of soluble GGTs. GGT A and B were monomeric proteins with an Mr of 61,000. The properties of GGT A and B were similar. Thus, bound GGTs were distinguished from soluble GGTs. The optimal pHs of soluble and bound GGTs were about 7.5. Both soluble and bound GGTs utilized glutathione, γ-L-glutamyl-p-nitroanilide, oxidized glutathione and the conjugate of glutathione with monobromobimane as substrates, and were inhibited by acivicin, but soluble GGTs were also distinguished from bound GGTs with regard to these properties.