/3-HYDROXYLATION OF TRIMETHYLLYSINE BY AN a-KETOGLUTARATE-DEPENDENT MITOCHONDRIAL DIOXYGENASE*

From the Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul, Minnesota 55108 Rat liver mitochondria were found to hydroxylate E-N- trimethyl+lysine to produce P-hydroxy-c-N-trimethyl-L-ly- sine, an intermediate in carnitine biosynthesis. The hydrox- ylating system requires a-ketoglutarate, Fez+, and ascor- bate, but does not require NADPH nor NADH. No activity was found in the microsomal or soluble fractions of liver extracts. The hydroxylated a-amino acid was isolated and characterized by column chromatography using Dowex 50- H+ and Chelex 100~CW+ resins and by high voltage paper electrophoresis. The enzymatically produced P-hydroxy-e- N-trimethyl+lysine was shown to be periodate-sensitive and one periodation product was characterized as y-buty- robetaine aldehyde. The hydroxylated product was acted upon by crystalline serine transhydroxymethylase (EC 2.1.2.1) to yield y-butyrobetaine aldehyde and glycine. Con- version of about 40% of the