| 1. |
- Åstot, C, et al.
(författare)
-
An alternative cytokinin biosynthesis pathway
- 2000
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 97:26, s. 14778-14783
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of de novo cytokinin biosynthesis in isopentenyltransferase (ipt)-transformed Arabidopsis thaliana, involving in vivo deuterium labeling and mass spectrometry, showed that the biosynthetic rate of zeatinriboside-5'-monophosphate was around 66-fold higher than that of isopentenyladenosine-5'-monophosphate (iPMP), the proposed primary product of the Agrobacterium ipt. Double tracer analysis, using [(2)H(6)] isopentenyladenosine and deuterium oxide, provided evidence for an alternative, iPMP-independent, biosynthetic pathway for zeatin-type cytokinins, present in both ipt-expressing and wild-type Arabidopsis thaliana. Reduction of the biosynthetic flux in the alternative pathway by use of mevastatin, an inhibitor for 3-hydroxy-3-methylglutaryl CoA reductase, indicated a terpenoid origin for the side-chain precursor of the iPMP independent pathway.
|
|
| 2. |
- Allen, P. D., et al.
(författare)
-
Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin
- 2000
-
Ingår i: Biochimica et Biophysica Acta - Molecular Basis of Disease. - 0925-4439 .- 1879-260X. ; 1500:2, s. 186-196
-
Tidskriftsartikel (refereegranskat)abstract
- Low-frequency low-field magnetic susceptibility measurements were made on four samples of mammalian tissue iron oxide deposits. The samples comprised: (1) horse spleen ferritin; (') dugong liver hemosiderin; (3) thalassemic human spleen ferritin; and (4) crude thalassemic human spleen hemosiderin. These samples were chosen because Mossbauer spectroscopic measurements on the samples indicated that they exemplified the variation in magnetic and mineral structure found in mammalian tissue iron oxide deposits. The AC-magnetic susceptometry yielded information on the magnetization kinetics of the four samples indicating samples 1, 2, and 3 to be superparamagnetic with values of around 10(11) s(-1) for the preexponential frequency factor in the Neel-Arrhenius equation and values for characteristic magnetic anisotropy energy barriers in the range 250-400 K. Sample 4 was indicated to he paramagnetic at all temperatures above 1.3 K. The AC-magnetic susceptometry data also indicated a larger magnetic anisotropy energy distribution in the dugong liver sample compared with samples 1 and 3 in agreement with previous Mossbauer spectroscopic data on these samples. At temperatures below 200 K, samples 1-3 exhibited Curie-Weiss law behavior, indicating weak particle-particle interactions tending to favor antiparallel alignment of the particle magnetic moments. These interactions were strongest for the dugong liver hemosiderin. possibly reflecting the smaller separation between mineral particles in this sample. This is the first magnetic susceptometry study of hemosiderin iron deposits and demonstrates that the AC-magnetic susceptometry technique is a fast and informative method of studying such tissue iron oxide deposits.
|
|
