Production of tyrosine and other aromatic compounds from phenylalanine by rumen microorganisms

Summary Rumen contents from three fistulated Japanese native goats fed Lucerne hay cubes (Medicago sativa) and concentrate mixture were collected to prepare the suspensions of mixed rumen bacteria (B), mixed protozoa (P) and a combination of the two (BP). Microbial suspensions were anaerobically incubated at 39°C for 12h with or without 1 MM ofl-phenylalanine (Phe). Phe, tyrosine (Tyr) and other related compounds in both supernatant and microbial hydrolysates of the incubations were analyzed by HPLC. Tyr can be produced from Phe not only by rumen bacteria but also by rumen protozoa. The production of Tyr during 12h incubation in B (183.6 mol/g MN) was 4.3 times higher than that in P. One of the intermediate products between Phe and Tyr seems to bep-hydroxyphenylacetic acid. The rate of the net degradation of Phe incubation in B (76.O mol/g MN/h) was 2.4 times higher than in P. In the case of all rumen microorganisms, degraded Phe was mainly (>53%) converted into phenylacetic acid. The production of benzoic acid was higher in P than in B suspensions. Small amount of phenylpyruvic acid was produced from Phe by both rumen bacteria and protozoa, but phenylpropionic acid and phenyllactic acid were produced only by rumen bacteria.     

The alpha-tubulin gene family in wheat (Triticum aestivum L.) and differential gene expression during cold acclimation.

The alpha-tubulins and beta-tubulins are the major constituents of microtubules, which have been recognized as important structural elements in cell growth and morphogenesis, and, recently, for their role in regulation and signal transduction. We have identified 15 full-length cDNAs for the members of the alpha-tubulin gene family in hexaploid bread wheat (Triticum aestivum L.). The genes were clustered into 5 homeologous groups of 3 genes. Representatives of the 5 homeologous groups were mapped to different chromosome arms, and the genome of origin was determined for each gene. Changes in mRNA levels were observed for the paralogous members of the gene family during cold acclimation. Three members of the family had initial decreases in mRNA levels in response to cold treatment, which were followed by increases, each with a different pattern of reinduction. One gene-family member showed increased mRNA for up to 14 d during cold acclimation and had decreased levels after 36 d of cold treatment; a fifth paralogous member of the gene family had slowly declining mRNA levels up to 36 d. Subtle differences in the level of gene expression among homeologs and large differences among paralogs were detected by comparing the relative abundance of wheat alpha-tubulin expressed sequence tags (ESTs) in public databases.     

Apolipoprotein A1 gene polymorphisms at the -75 bp and +83/ 84 bp polymorphic sites in healthy Omanis compared with world populations

The relative frequencies of the *A allele of the APOA1 gene at -75 bp (M1-) and the C or T +83/+ 84 bp allele (M2-) varied significantly between populations. We found the frequencies of M1- and M2- to be 0.22 and 0.067, respectively, in 150 healthy Omanis. These frequencies were compared to frequencies found in other world populations.     

A multi-enzyme cascade of hemoglobin proteolysis in the intestine of blood-feeding hookworms

Blood-feeding pathogens digest hemoglobin (Hb) as a source of nutrition, but little is known about this process in multicellular parasites. The intestinal brush border membrane of the canine hookworm, Ancylostoma caninum, contains aspartic proteases (APR-1), cysteine proteases (CP-2), and metalloproteases (MEP-1), the first of which is known to digest Hb. We now show that Hb is degraded by a multi-enzyme, synergistic cascade of proteolysis. Recombinant APR-1 and CP-2, but not MEP-1, digested native Hb and denatured globin. MEP-1, however, did cleave globin fragments that had undergone prior digestion by APR-1 and CP-2. Proteolytic cleavage sites within the Hb alpha and beta chains were determined for the three enzymes, identifying a total of 131 cleavage sites. By scanning synthetic combinatorial peptide libraries with each enzyme, we compared the preferred residues cleaved in the libraries with the known cleavage sites within Hb. The semi-ordered pathway of Hb digestion described here is surprisingly similar to that used by Plasmodium to digest Hb and provides a potential mechanism by which these hemoglobinases are efficacious vaccines in animal models of hookworm infection.     

Purification, physicochemical characterization, saccharide specificity, and chemical modification of a Gal/GalNAc specific lectin from the seeds of Trichosanthes dioica

A new galactose-specific lectin has been purified from the extracts of Trichosanthes dioica seeds by affinity chromatography on cross-linked guar gum. The purified lectin (T. dioica seed lectin, TDSL) moved as a single symmetrical peak on gel filtration on Superose-12 in the presence of 0.1 M lactose with an M(r) of 55 kDa. In the absence of ligand, the movement was retarded, indicating a possible interaction of the lectin with the column matrix. In SDS-PAGE, in the presence of beta-mercaptoethanol, two non-identical bands of M(r) 24 and 37 kDa were observed, whereas in the absence of beta-mercaptoethanol, the lectin yielded a single band corresponding to approximately 55,000 Da, indicating that the two subunits of TDSL are connected by one or more disulfide bridges. TDSL is a glycoprotein with about 4.9% covalently bound neutral sugar. Analysis of near-UV CD spectrum by three different methods (CDSSTR, CONTINLL, and SELCON3) shows that TDSL contains 13.3% alpha-helix, 36.7% beta-sheet, 19.4% beta-turns, and 31.6% unordered structure. Among a battery of sugars investigated, TDSL was inhibited strongly by beta-d-galactopyranosides, with 4-methylumbelliferyl-beta-d-galactopyranoside being the best ligand. Chemical modification studies indicate that tyrosine residues are important for the carbohydrate-binding and hemagglutinating activities of the lectin. A partial protection was observed when the tyrosine modification was performed in the presence of 0.2 M lactose. The tryptophan residues of TDSL appear to be buried in the protein interior as they could not be modified under native conditions, whereas upon denaturation with 8 M urea two Trp residues could be selectively modified by N-bromosuccinimide. The subunit composition and size, secondary structure, and sugar specificity of this lectin are similar to those of type-2 ribosome inactivating proteins, suggesting that TDSL may belong to this protein family.