Stereoselective hydrolysis of dl-menthyl succinate by gel-entrapped Rhodotorula minuta var. texensis cells in organic solvent

Summary dl-Menthyl succinate was successfully hydrolyzed stereoselectively by Rhodotorula minuta var. texensis cells entrapped within photo-crosslinked or polyurethane resin gels in water-saturated n-heptane. The hydrolyzed product was found to be pure l-menthol. The catalytic activity of the immobilized cells, especially those entrapped in urethane polymers, was far more stable than that of the free cells. The half-life of the polyurethaneentrapped cells was estimated to be 55–63 days in the organic solvent.Dedicated to the 65th birthday od Professor Dr. G. Manecke     

Circadian alterations in tubular structures on the outer mitochondrial membrane of rat hepatocytes

Summary The ontogeny and distribution of immunoreactive motilin and secretin were studied in the gastro-entero-pancreatic (GEP) system of human fetuses, aged 5–24 weeks, using an indirect immunocytochemical method. Several controls to check for the specificity of the immunoperoxidase staining were performed. The first motilin- and secretin-containing cells were observed in the duodenal and jejunal mucosa in fetuses at a gestational age of 16 weeks. These immunoreactive cells were located in the glands of Lieberkühn and in the villi. No immunoreactive cells were present in the oxyntic and pyloric mucosa, ileum, colon and endocrine pancreas. These observations indicate that the motilin- and secretin-containing cells detected by our antisera appear (i) in the same organs of the fetus where they are also detectable in the adult, and (ii) after the completion of histogenesis of the gastro-entero-pancreatic (GEP) system.     

Reduction by a model of NAD(P)H: XI. Stereochemistry of a lactate dehydrogenase-model reaction

Stereochemistry of the biomimetic reduction of α-keto esters with NAD(P)H-model compounds has been investigated. The model compound with the R-configuration reduces the α-keto esters to the (R)-α-hydroxy esters, whereas (S)-α-hydroxy esters are afforded by the reduction with the S-configurational model compounds. It has been concluded that pro-R and -S hydrogens of the model compounds with R- and S-configuration, respectively, contribute predominantly to the reduction.     

Effects of phospholipids on L-lactate dehydrogenase from membranes of Escherichia coli. Activation and stabilization of the enzyme with phospholipids.

Membrane-bound L-lactate dehydrogenase was freed from the detergent used during purification. The detergent-free enzyme had about one-half the specific activity of the enzyme in 1.0% Tween 80, and was only partially sensitive to the specific antibody. This enzyme was activated about 3-fold with phosphatidylglycerol, cardiolipin, or a mixture of phospholipids. The phospholipid-activated enzyme had a similar Km value for L-lactate to that of the membrane enzyme and was completely inhibited by the specific antibody. On heat treatment, the phospholipid-activated enzyme was more stable than detergent-free enzyme and was as stable as membrane-bound enzyme. The alpha helical content of the enzyme increased 1.7-fold during preincubation with these lipids and the alpha helix became more stable during heat treatment than that of the detergent-free enzyme. These results suggest that the enzyme showed monomolecular dispersion in the lipid bilayer and that its conformation, including its active site and secondary structure, was different from that of the detergent-free enzyme. Phosphatidylethanolamine, dilauroyl lecithin and lecithin from egg yolk had none of the above effects on the activity or the secondary structure of the enzyme. On the other hand, mixtures of each of these lipids and cholate had essentially similar effects to phosphatidylglycerol.     

Kinetics of substrate utilization in adenine-limited chemostat cultures of Bacillus subtilis KYA741.

The specific rates of limiting substrate utilization were investigated in adenine- or glucose-limited chemostat cultures of Bacillus subtilis KYA741, an adenine-requiring strain, at 37 degrees C. With the glucose-limited cultures, the specific rate of glucose consumption versus dilution rate gave a linear relationship from which the true growth yield and maintenance coefficient were determined to be 0.09 mg of bacteria per mg of glucose and 0.2 mg of glucose per mg of bacteria per h, respectively. With the adenine-limited cultures, adenine as the limiting substrate was not completely consumed at lower dilution rates (e.g., D less than 0.1), unlike in the glucose-limited cultures. When a linear relationship of specific rate of adenine consumption versus dilution rate was extrapolated to zero dilution rate, a negative value for the specific rate of adenine consumption, -0.01 mg of adenine per mg of bacteria per h, was obtained, giving a true growth yield for adenine of 5.2 mg of bacteria per mg of adenine. On the other hand, the maintenance coefficient of oxygen uptake gave a positive value of 8.1 x 10(-3) mmol/mg of bacteria per h. Based on previous results showing that adenine is resupplied by lysing cells, we developed kinetic models of adenine utilization and cell growth that gave a good estimation of the peculiar behavior of cell growth and adenine utilization in adenine-limited chemostat cultures.     

The gene and deduced protein sequences of the zymogen of Aspergillus niger acid proteinase A

Proteinase A obtained from the culture medium of Aspergillus niger var. macrosporus is a unique acid endopeptidase that is insensitive (or less sensitive) to specific inhibitors of ordinary acid or aspartic proteinases, such as pepstatin, diazoacetyl-DL-norleucine methyl ester, and 1,2-epoxy-3-(p-nitrophenoxy)-propane. In the preceding paper (Takahashi, K., Inoue, H., Sakai, K., Kohama, T., Kitahara, S., Takishima, K., Tanji, M., Athauda, S. B. P., Takahashi, T., Akanuma, H., Mamiya, G., Yamasaki, M. J. Biol. Chem. 266, 19480-19483), we reported the complete primary structure of the mature enzyme determined at the protein level. The enzyme has a unique two-chain structure with a 39-residue light (L) chain and a 173-residue heavy (H) chain linked noncovalently. As an extension of this study, we isolated genomic and cDNA clones encoding this proteinase and determined their nucleotide sequences. To isolate a genomic clone, the genomic DNA was selectively amplified by polymerase chain reaction using mixed oligonucleotide primers designed from the amino acid sequence of the H chain, and a specific probe thus generated was used for screening a lambda gt10 genomic library. A cDNA for the enzyme was also selectively amplified by polymerase chain reaction using primers synthesized based on the sequence of the genomic DNA. Sequencing of the cloned genomic DNA and cDNA revealed the nucleotide sequence of the structural gene for the enzyme of 846 base pairs without introns. It encodes the precursor form of proteinase A, including an NH2-terminal preprosequence of 59 residues, the L chain of 39 residues, an intervening sequence of 11 residues, and the H chain of 173 residues linked in that order. Thus, proteinase A is thought to be synthesized as a single peptide chain preproenzyme of 282 residues, which is processed to generate the mature two-chain form.     

Role of glycosaminoglycans in the regulation of T cell proliferation induced by thymic stroma-derived T cell growth factor

The present study investigates the regulatory effects of glycosaminoglycans such as heparin and heparan sulfate on T cell proliferation induced by thymic stromal cell monolayer or its derived T cell growth factor (TCGF). A thymic stromal cell clone (MRL104.8a) supported the growth of Ag-specific, IL-2-dependent Th cell clone (9-16) in the absence of Ag and IL-2 by producing a unique TCGF designated as thymic stroma-derived T cell growth factor (TSTGF). The addition of heparin to cultures in which the growth of 9-16 Th cells was otherwise stimulated by the MRL104.8a monolayer or a semipurified sample of the TSTGF resulted in heparin dose-dependent inhibition of 9-16 Th proliferation. The dose of heparin required for inducing 50% reduction of TSTGF-induced proliferation of Th at a given cell number was found to be proportional to the magnitude of the TSTGF added to cultures, suggesting that heparin exerted its inhibitory effect by binding to the TSTGF rather than by acting on Th cells. A similar growth-inhibiting effect of heparin was observed in IL-7-dependent proliferation of pre-B cell line or Th, but not in IL-2-dependent T cell proliferation or IL-3-dependent myeloid cell proliferation. A strong affinity of TSTGF and IL-7 for heparin was confirmed by the fact that both TSTGF and IL-7 adhered to columns of heparin-agarose and were eluted by salt. When various glycosaminoglycans were tested for the heparin-like Th growth-regulatory capacity, heparan sulfate exhibited Th growth-inhibiting ability comparable to that observed for heparin. These results indicate that the activity of thymic and/or bone marrow stroma-derived lymphocyte growth factor (TSTGF/IL-7) but not of Th-producing TCGF (IL-2) is negatively regulated by heparin or heparan sulfate, which would represent major glycosaminoglycans in the extra-cellular matrix of stromal cells.     

The complete amino acid sequence of ribonuclease from the seeds of bitter gourd (Momordica charantia)

The complete amino acid sequence of ribonuclease (RNase MC) from the seeds of bitter gourd (Momordica charantia) has been determined. This has been achieved by the sequence analysis of peptides derived by enzymatic digestion with trypsin, lysylendopeptidase, and chymotrypsin, as well as by chemical cleavage with cyanogen bromide. The protein contains 191 amino acid residues and has a calculated molecular mass of 21,259 Da. Comparison of this sequence with sequences of the fungal RNases, RNase T2, and RNase Rh, revealed that there are highly conserved residues at positions 32-38 (TXHGLWP) and 81-92 (FWXHEWXKHGTC). Furthermore, the sequence of RNase MC was found to be homologous to those of Nicotiana alata S-glycoproteins involved in self-incompatibility sharing 41% identical residues.     

Effect of cavity-modulating mutations on the stability of Escherichia coli ribonuclease HI.

The size of the cavity around Ser68 of Escherichia coli ribonuclease HI was modulated by amino acid substitutions to examine the effects on the stability of the enzyme. Five mutant proteins, Ser68----Gly, Ser68----Ala, Ser68----Thr, Ser68----Val and Ser68----Leu, were constructed. Each of the mutant proteins exhibited at least 40% of the enzyme activity of the wild-type protein. The stabilities of the mutant proteins were determined from urea-denaturation and thermal-denaturation curves. Among the five mutations, only the Ser----Val mutation resulted in an increase in the stability of the enzyme. The melting temperature, tm, at pH 3.0 of the mutant protein Ser68----Val was increased by 1.9 degrees C. Its free-energy change of unfolding in the absence of urea, delta G(H2O), and the midpoint of the denaturation curve, [D]1/2, were also increased by 5.4 kJ/mol and 0.18 M, respectively. The increase in the stability of the enzyme is probably due to the filling of the cavity space around Ser68 by valine. However, the mutation of Ser68 to glycine or leucine residues resulted in a considerable decrease in stability. In these cases, some conformational changes occur, as suggested by the CD and 1H-NMR spectra of these mutant proteins.