UbcH5 enzymes are human homologs of the yeast UBC4/5 family and play many important regulatory roles in inflammation and cancer. UbcH5a mediates the degradation of a myriad of short-lived regulatory proteins (such as p53 in the presence of E6/E6-AP or MDM2, c-Fos, IκBα, p105) and abnormal proteins. UbcH5a has 89% and 88% sequence identity with UbcH5b and UbcH5c respectively. This enzyme has a mutation of the active site from cysteine to serine which abolishes the ability of UbcH5a to transfer ubiquitin to an accepting E3 protein. Ideal for use as a negative or competitive control, or to study protein-protein interactions. This protein has an N-terminal GST tag.