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 an active site mutation from cysteine to serine which abolishes the ability of UbcH5a to transfer ubiquitin to an E3 protein. Ideal for use as a negative or competitive control, or to study protein-protein interactions.