The pathway from UDP-glucose to UDP-xylose has been characterised in differentiating tobacco tissue. A xylogenic suspension cell culture of tobacco has been used as a source for the purification of the enzymes responsible for the oxidation of UDP-glucose to UDP-glucuronic acid and its subsequent decarboxylation to UDP-xylose. Protein purification and transcriptional studies show that two possible candidates can contribute to the first reaction. Most of the enzyme activity in the cultured cells could be accounted for by a protein with an Mr of 43 kDa which had dual specificity for UDP-glucose and ethanol. The cognate cDNA, with similarity to alcohol dehydrogenases (NtADH2) was expressed in E. coli to confirm the dual specificity. A second UDP-glucose dehydrogenase, corresponding to the monospecific form, ubiquitous amongst plants and animals, could not be purified from the tobacco cell cultures. However, two cDNAs were cloned with high similarity to the family of UDP-glucose dehydrogenases. Transcripts of both types of dehydrogenase showed highest expression in tissues undergoing secondary wall synthesis. The UDP-glucuronate decarboxylase was purified as polypeptides of Mr 87 and 40 kDa. Peptide fingerprinting of the latter polypeptide identified it as a form of UDP-glucuronate decarboxylase and functionality was established by expressing the cognate cDNA in E. coli. Expression of 40 kDa polypeptide and its corresponding mRNA was also found to be highest in tissues associated with secondary wall formation.

ABSTRACIWe studied the organization of the K light chain genes in germ-line (sperm) and somatic (embryo) tissues. We constructed a plasmid containing a DNA insert coding for the K chain MOPC 167 and used the Southern blotting technique to determine the organization of K variable and constant region genes. In the haploid genome of the mouse there is only one constant region gene detectable and it has the same organization in sperm and embryo DNAs. There are several variable region genes in sperm and embryo that are related to the Vk167 gene. The organization of the V genes in sperm and embryo DNAs is identical. These results show that there is no rearrangement of variable region genes (or "minigenes") during early embryogenesis.The polypeptides that form antibody molecules can be divided into two-distinct parts, the variable (V) and the constant (C) region. From RNA-DNA hybridization studies, only a few copies of a particular C region seem to be present in the genome (1-11). The number of V region genes present in the germ line is still not resolved. Because the V regions determine the antibody specificity, the question of the origin of antibody diversity is an integral part of the number and organization of the V region genes. Several hypotheses have been proposed to explain the origin of antibody diversity. The strict germ-line hypothesis proposes that there are multiple V region genes and each antibody-producing cell chooses to express only one of these genes from the inherited V region repertoire (12). The various somatic diversification hypotheses explain the origin of antibody diversity quite differently. It is assumed that the germ line contains only a few V region genes and these are somatically diversified during ontogeny in order to yield many different V regions. A strict mutation hypothesis proposes that mutations (simple base changes) occur during differentiation of precursor cells into antibody-producing cells (13,14). These mutations may occur in the hypervariable part of the V region or they may occur randomly throughout the V region gene. The somatic recombination hypothesis postulates a limited number of V genes in the germ line which undergo unequal crossing-over during ontogeny to form recombined V genes, thereby expanding the V region information that is expressed (15, 16).Wu and Kabat (17) pointed out that amino acid sequence analysis of several hundred light chain V regions suggested a division of V regions into four "framework" regions with very little variability (FR1, FR2, FR3, and FR4) and three hypervariable regions (HV1, HV2, and HV3) that exhibit extensive sequence diversity. Kabat and others later proposed that each of these V region segments was a germ-line minigene that was inherited independently (18)(19)(20). By these hypotheses, subgenicThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 1106 elements representing all po...

Sulfotransferase 1A1 (SULT1A1) (thermostable phenol sulfotransferase, TS PST1, P-PST) is important in the metabolism of thyroid hormones. SULT1A1 isolated from human platelets displays wide individual variations not only in the levels of activity, but also in thermal stability. The activity of the allelic variant or allozyme SULT1A1*1, which possesses an arginine at amino acid position 213 (Arg213) has been shown to be more thermostable than the activity of the SULT1A1*2 allozyme which possesses a histidine at this position (His213) when using p-nitrophenol as the substrate. We isolated a SULT1A1*1 cDNA from a human liver cDNA library and expressed both SULT1A1*1 and SULT1A1*2 in eukaryotic cells. The allozymes were assayed using iodothyronines as the substrates and their biochemical properties were compared. SULT1A1*1 activity was more thermostable and more sensitive to NaCl than was SULT1A1*2 activity when assayed with 3,5,3 -triiodothyronine (T 3 ). Sensitivities to 2,6-dichloro-4-nitrophenol (DCNP) and apparent K m values for SULT1A1*1 and for SULT1A1*2 with iodothyronines were similar. Based on K m values, the preferences of these SULT1A1 allozymes for iodothyronine substrates were the same (3,3 -diiodothyronine (3,3 -T 2 )>3 , 5 ,3-triiodothyronine (rT 3 )>T 3 >thyroxine (T 4 )> >3,5-diiodothyronine (3,5-T 2 )). SULT1A1*1 activity was significantly higher than the SULT1A1*2 activity with T 3 as the substrate. Potential differences in thyroid hormone sulfation between individuals with predominant SULT1A1*1 versus SULT1A1*2 allozymes are most likely due to differences in catalytic activity rather than substrate specifity.