The subcellular biochemistry of thyroid

Characterization of the in vitro conversion of dolichol to dolichoate in bovine thyroid

The enzymic conversion of dolichol into dolichoic acid has been studied in bovine thyroid subcellular fractions using [1-3H]dolichol as a substrate. The presence of conversion activity could be demonstrated in both the mitochondrial- and supernatant fractions. Investigation of cofactor requirements revealed that NAD+ was essential for reaching optimal activity. From kinetic studies Km-values of 3.5-4 microM and 0.29 mM could be calculated for, respectively, dolichol and NAD+ using the mitochondrial fraction as an enzyme source. No inhibitory effects from ethanol or pyrazole were detected suggesting that alcohol dehydrogenase is not involved in the dolichol-->dolichoate conversion as observed in a bovine thyroid mitochondrial fraction. From inhibitor studies the conversion system behaves distinctly differently from the NADP(+)-depending microsomal oxidoreductase as well as from catalase. The conversion activity in the supernatant on the other hand must be ascribed, at least partially, to a side activity of alcohol dehydrogenase.

Identification and characterization of dolichyl dolichoate, a novel isoprenoic derivative in bovine thyroid

Inspection of the TLC pattern of the neutral lipid fraction of bovine thyroid reveals, in addition to cholesteryl esters and dolichyl fatty acid esters, the presence of a not yet identified compound in the most apolar lipid region. This unknown compound was purified on a preparative scale by silicic acid column chromatography, Lipidex-5000 gel-filtration chromatography and preparative thin-layer chromatography. By chemical (hydrolysis and reduction) and spectroscopic (ultraviolet, infrared, NMR, mass spectroscopy) methods this lipid was identified as dolichyl dolichoate. The homologue pattern was analyzed, by HPLC and FDMS, respectively.

A study on the RNA polymerase activities in bovine thyroid nuclei isolated in isotonic sucrose, hypertonic sucrose or in anhydrous glycerol media. Influence of the isolation procedure on the electrophoretic pattern of acid soluble nuclear proteins

After differential pelleting of bovine thyroid bound RNA polymerase II was the more enriched enzyme activity in the nuclear fraction, and coincided best with the DNA profile. The RNA polymerase I + III activity was compared in nuclear fractions isolated either in 0.25 M sucrose (wet tissue) or in anhydrous glycerol (lyophilized tissue) or in 2.4 M sucrose (lyophilized tissue). Although the nuclei were more resistant to the isolation procedure in glycerol, more proteins were extracted by that procedure than during the isolation in 2.4 M sucrose. With the 2.4 M sucrose method a twofold enrichment of RNA polymerase I + III activity in respect to DNA occurred in the nuclei pointing to an exclusive localization of these activities within the nucleus. Using the same isolation procedure the different classes of histones were better resolved upon polyacrylamide gel electrophoresis.