Differences in expression and activity of β , β ′‐carotene‐15,15′‐ oxygenase in liver and duodenum of cattle with yellow or white fat

Pasture‐fed cattle show yellow pigmentation of their fat due to β ‐carotene stored in this tissue. β , β ′‐Carotene‐15,15′‐oxygenase ( β CO) is an enzyme expressed in different tissues, and it cleaves β ‐carotene into retinal. We compared the expression and activity of β CO in duodenum and liver of cattle with pigmented or non‐pigmented fat. In the duodenum, in situ hybridizations showed expression of β CO in epithelial cells and crypts of the mucosa that was similar in animals from pigmented and non‐pigmented fat; liver showed diffuse signal at lobules, but pigmented animals showed higher signals near the portal space. Analyses by real‐time reverse‐transcription polymerase chain reaction also showed amplification of mRNA for β CO in duodenum and liver, with no difference between pigmented or non‐pigmented animals. Enzyme activity was similar in the duodenum, but pigmented animals had higher enzyme activity (p = 0.004) in liver. Cattle with pigmented fat had higher expression and activity of β CO in liver, but its level was not high enough to prevent the storage of β ‐carotene in adipose tissues.