Cell extracts of Methanobacterium thermoautotrophicum (strain AH) were found to perform a hydrogendependent reduction of factor 390 (F390), the 8-adenylyl derivative of coenzyme F420. Upon resolution of cell extracts, F390-reducing activity copurified with the coenzyme F420-dependent hydrogenase. This Methanogenic bacteria constitute a group of strictly anaerobic microorganisms that obtain their energy for biosynthesis of carbon in the cell from the conversion of onecarbon substrates or acetate to CH4. During the last decade, several novel coenzymes have been isolated and shown to participate in the methanogenic pathway (11,17). A few years ago, this list of mostly unique compounds became expanded with the discovery of two chromophores showing absorbance maxima at 390 nm (8). These compounds were identified as derivatives of coenzyme F420 (an 8-hydroxy-5-deazaflavin) in which AMP or GMP is linked to the deazaflavin via the 8-hydroxy position and are therefore named factor 390 (F390)-A and F390-G (Fig. 1) (8). These chromophores could be isolated only when growing cultures of Methanobacterium thermoautotrophicum were exposed to oxygen (7,8,16). Subsequent removal of oxygen from the gas phase resulted in the disappearance of the F390 compounds with the concomitant formation of coenzyme F420 (7, 16).Recently, enzymatic synthesis of F390 was demonstrated to occur in cell extracts of the organism (13). The reaction used oxidized coenzyme F420 and ATP as substrates and proceeded only when the extracts had been pretreated with oxygen. The ability to synthesize F390 was rapidly but reversibly lost when the extracts were brought under reducing conditions (13).In order to ascribe a physiological role to factor(s) F390, the potential for interconversion of this compound(s) in cell extracts was further examined. In this article, we report the H2-dependent reduction of F390-A and its enzymatic hydrolysis to coenzyme F420 by cell extracts of M. thermoautotrophicum. Optimal conditions for the F390-reducing activity and F390 hydrolase are described and compared with those of the coenzyme F420-reducing hydrogenase and the

The objective of this study was to analyze the changes in tissue architecture and matrix composition during healing of palatal wounds of immature rats, and to compare this with rats of the same age that did not receive mucoperiosteal wounds. Wounds were made in the mucoperiosteum of the palate of 35-d-old rats. Samples were evaluated histologically at numerous points in time after wounding. The DNA, hydroxyproline and sulphated glycosaminoglycan contents were determined at 8, 15, 30, and 60 d post-wounding. Eight-d-old granulation tissue contained 43% less hydroxyproline, and 100% more glycosaminoglycans and cells than unwounded palatal tissue of 43-d-old rats. Sixty-d-old wounds contained 100% more DNA and 39% more hydroxyproline than unwounded tissue of 95-d-old rats. At the same time, densely packed and transversely aligned collagen fibres were present. It is concluded that palatal mucoperiosteal wounds made in 35-d-old rats heal with distinct scar tissue formation. The scar contains more collagen than non-wounded palatal tissue of rats of the same age. Therefore, this model may be of use for the development of therapies aiming to reduce palatal scarring.

Intact sesamoid bones from bovine metacarpophalangeal joints were cultured with retinoic acid for 9 days and allowed to recover in control medium for up to 17 days. Retinoic acid (300 ng/ml) induced 91.8% inhibition of glycosaminoglycan (GAG) synthesis and 50.6% loss of sulfated GAGs from the cartilage. Retinoic acid also induced 38.2% loss of hyaluronate from the matrix. The synthesis and content of the large aggregating proteoglycan (aggrecan) were preferentially decreased compared with that of the small nonaggregating species. The aggrecan synthesized was similar to control aggrecan in size, aggregation capacity, and composition of its GAGs. GAG synthesis was almost completely restored in control medium within the next 6 days. The GAGs synthesized during recovery were slightly shorter than control GAGs and showed a higher ratio of chondroitin-6-sulfate over chondroitin-4-sulfate. Neither the proteoglycan content nor the hyaluronate content recovered within 17 days. The aggregation capacity of newly synthesized aggrecan was normal. However, the retention of proteoglycans synthesized in the recovery period was much lower in treated cartilage than in control cartilage (T1/2 of 17 and 38 days, respectively). In conclusion, the retinoic-acid-induced proteoglycan depletion was irreversible in spite of the restored synthesis of aggrecan with a normal aggregation capacity. The reduced retention of newly synthesized aggrecan during recovery might be caused by a lack of hyaluronate. This model seems suitable to study aspects of cartilage destruction and repair.