Preparation of L-tyrosine-ring- 14 C, L-DOPA-ring- 14 C and related metabolites

The reversibility of the tyrosine phenol-lyase reaction has been utilized to develop a simple system in which phenol-¹⁴C is incorporated into l-tyrosine in high yield. By use of mushroom tyrosinase, catechol-¹⁴C can be prepared from phenol-¹⁴C and l-DOPA-¹⁴C from l-tyrosine-¹⁴C. Catechol-¹⁴C can also be incorporated into l-DOPA-¹⁴C by use of tyrosine phenol-lyase, giving the possibility of preparing DOPA with two labeling patterns in the ring when starting with phenol-¹⁴C. Two further tyrosine metabolites, para-coumaric acid and homogentisic acid, have also been enzymatically prepared with ¹⁴C in the ring.     

14C] GABA and [14C]GABA-pantoyl metabolism in mice

It is shown that more than 90% of the labelled substance D-[1-14C] calcium homopantotenate is rapidly removed from the organism with urea; 6-8% are products of its transformation, among them GABA is identified. An insignificant transformation of D-[1-14C] calcium homopantotenate up to 14CO2 is observed. After the preparation administration only unchanged D-[1-14C] calcium homopantotenate was found in the tissues, except of the liver where, as in urea, there is a nonidentified product with small Rf. [1-14C] GABA is rapidly transformed to 14CO2 and only its insignificant part is removed with urea, chiefly as products of transformation.     

Metabolism of phytol-U-14C and phytanic acid-U-14C in the rat

The metabolism of uniformly-labeled (14)C-phytol, (14)C-phytenic acid, and (14)C-phytanic acid was studied in the rat. Conversion of both phytol and phytenic acid to phytanic acid was demonstrated. Tracer doses of phytol-U-(14)C given orally were well absorbed (30-66%), and approximately 30% of the absorbed dose was converted to (14)CO(2) in 18 hr. After intravenous injection, 20% appeared in (14)CO(2) in 4 hr. Phytanic acid-U-(14)C given intravenously was oxidized at a comparable rate (22-37% in 4 hr) and was as rapidly oxidized as palmitic acid-1-(14)C (21% in 4 hr). Metabolism of these substrates was also studied in rats previously maintained on a diet containing 5% phytol by weight, which causes accumulation of phytanic acid, phytenic acid, and, to a lesser extent, phytol in blood and tissues. Despite the large body pools of preformed, unlabeled substrate in these animals, the fraction of an administered dose of phytol-U-(14)C or phytanic acid-U-(14)C converted to (14)CO(2) was not significantly diminished. These studies indicate that the rat has an appreciable capacity to degrade the highly branched carbon skeleton of phytol and its derivatives. Twenty-four hours after administration of phytol-U-(14)C, the lipid radioactivity remaining in the body was widely distributed among the tissues, highest concentrations being found in liver and adipose tissue. Four hours after intravenous administration of phytanic acid-U-(14)C, all of the major lipid classes in the liver contained radioactivity, most in triglycerides and phospholipids and least in cholesterol esters and lower glycerides. There was no demonstrable incorporation of mevalonate-2-(14)C or acetate-1-(14)C into liver phytanic acid when they were given intravenously to a rat previously fed phytol. Endogenous biosynthesis, if it occurs at all, must be extremely limited.     

Thermophilic Anaerobic Biodegradation of [14C]Lignin, [14C]Cellulose, and [14C]Lignocellulose Preparations

Thermophilic (55°C) anaerobic enrichment cultures were incubated with [¹⁴C-lignin]lignocellulose, [¹⁴C-polysaccharide]lignocellulose, and kraft [¹⁴C]lignin prepared from slash pine, Pinus elliottii, and ¹⁴C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Lipogenesis from glucose-2- 14 C and acetate-1- 14 C in aorta

Lipogenesis was measured with glucose-2-(14)C and acetate-1-(14)C in the everted aortas of normal and atherosclerotic rabbits. More glucose-2-(14)C than acetate-1-(14)C was incorporated into lipids in both the normal and the atherosclerotic aorta. Radiocarbon from glucose-2-(14)C appeared mainly in triglycerides and phospholipids with a small amount in cholesteryl esters. Incorporation increased almost threefold with atherosclerosis, most of the radioactivity being in the glycerol moiety; radioactivity was predominantly in carbon 2 of glycerol. About 70% of the acetate-1-(14)C incorporated into phospholipids and triglycerides was in the fatty acids, and the remainder was in glyceride-glycerol; 98% of the radioactivity in cholesteryl esters was in the fatty acid moiety. Incorporation into cholesteryl esters was increased most during the development of atherosclerosis. Fatty acid synthesis was similar from both acetate-1-(14)C and the 2 carbon unit derived from glucose-2-(14)C, viz., predominantly de novo synthesis of fatty acids with 14 and 16 carbon atoms, and elongation for those of 18 carbons and longer.