Mitochondrial metabolism of guanine nucleotides. Possible role of guanosine

The catabolism of intramitochondrial guanine nucleotides was examined. During 30 min incubation of rat liver mitochondria at 37 degrees C in the presence of oligomycin and carboxyatractyloside, guanine and xanthine were formed and appeared in the medium. Under these conditions, the direct conversion of GMP to guanine by hypoxanthine-guanine phosphoribosyltransferase is suggested to be the main catabolic route within the organelles. Only very small amounts of guanosine were produced and detected both inside and outside the organelles. [14C]Guanosine and [14C]inosine were taken up by the mitochondria. Therefore, guanosine is suggested to be a precursor of intramitochondrial guanine nucleotides.

Does the human body produce a substance similar to caffeine?

The idea that the human body probably produces a substance similar to caffeine came to my mind after reviewing the literature on the "restless legs syndrome". This syndrome is a disorder in which the afflicted individual feels an irresistible urge to move the legs, generally when sitting or lying down, and especially in bed, at night, just prior to getting to sleep. The patient has an extremely unpleasant deep discomfort inside the calves, requiring that the legs be moved(1). The "restless legs syndrome" has been described in persons who consume a lot of caffeine(2,3), in patients with iron deficiency anemia(4), and in patients with chronic renal failure(5). Since this syndrome occurs in persons who indulge in caffeine consumption as well as in patients with iron deficiency and patients with chronic renal failure, it is tempting to postulate that the human body- in cases of iron deficiency and chronic renal failure -produces a substance similar to caffeine. The following discussion entertains the hypothetical route that might be involved in the formation of this substance.

Purine ribonucleotide biosynthesis, interconversion and catabolism in mouse brain in vitro

The relative rates of the synthetic, interconversion and catabolic reactions of purine metabolism in chopped mouse cerebrum were studied. The rates of incorporation of [(14)C]adenine and [(14)C]hypoxanthine into purine ribonucleotides were much less than the potential activities of adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase, and the rates of incorporation were stimulated by the addition of guanosine to the incubation mixture. The availability of ribose phosphates may be a limiting factor for the formation of ribonucleotides from purine bases. The rate of incorporation of [(14)C]adenosine into purine ribonucleotides was at least seven- to eight-fold higher than that of adenine. The radioactivity in adenine ribonucleotides synthesized from adenine and hypoxanthine was about 100- and ten-fold respectively higher than that in the radioactive guanine ribonucleotides. The conversion of inosinate into guanine ribonucleotides was probably limited by the amount of inosinate available, and the conversion of adenine ribonucleotides into guanine ribonucleotides was probably limited by the activity of adenylate deaminase. The rate of catabolism of [(14)C]adenosine was low in comparison with its rate of utilization for ribonucleotide synthesis. A fraction of the [(14)C]hypoxanthine was catabolized to xanthine and urate. [(14)C]Guanine was completely converted into xanthine, mostly by the guanine deaminase that was released during incubation of chopped mouse cerebrum.

Pathways of purine ribonucleotide catabolism in Ehrlich ascites tumor cells in vitro

Ehrlich ascites tumor cells incubated in vitro with adenine-14C catabolized up to 20% of the radioactive nucleotides which were formed, principally via dephosphorylation of inosinate and xanthylate, with small amounts of adenylate and guanylate broken down. Cells incubated with hypoxanthine-14C catabolized a much larger proportion of nucleotides, principally via dephosphorylation of inosinate and xanthylate; guanylate was also broken down. Catabolic products of guanine-14C in these cells were xanthine, which was formed directly from guanine, and guanosine which at least in part was formed via dephosphorylation of guanylate.

Inhibition of carotenoid hydroxylation in Staphylococcus aureus by mixed-function oxidase inhibitors

Compounds known to be inhibitors of mixed-function oxidase systems inhibited the aerobic synthesis of hydroxylated carotenoids in Staphylococcus aureus U-71. Growth of the cells in the presence of 2-diethylaminoethyl-2,2-diphenyl valerate, 2,4-dichloro-6-phenylphenoxyethylamine, 2,4-dichloro-6-phenylphenoxyethyldiethylamine, and piperonyl butoxide reduced the levels of the rubixanthins found in stationary-phase cells by 75 to 97%. In cells grown with mevalonate-2-(14)C, the turnover rate of phytoene was reduced and the turnover rate of phytofluenol was increased in the presence of these inhibitors. The zeta- and delta-carotenes, which turn over in the absence of the inhibitors, accumulated (14)C in the presence of the inhibitors. This suggested that a mixed-function oxidase was responsible for the aerobic hydroxylation of delta-carotene in S. aureus U-71.