Deactivation ofCandida rugosa lipase

Summary Deactivation ofCandida rugosa lipase was found to be complex. Hydrophobic interaction induced by iso-octane influenced the initial phase of deactivation, and increased the turn-over rate of the intermediate in the transition phase. After urea-treatment the structure of the last phase was not further influenced by thermal treatment, whereas that of initial phase was more sensitive to temperature change. Charge interaction was important in maintaining the structure during the deactivation, and especially anion charge might be a major factor.     

Novel stabilization of phenylalanine ammonia-lyase catalyst during bioconversion of trans-cinnamic acid to l-phenylalanine

Summary Production of l-phenylalanine from trans-cinnamic acid using isolate SPA10 cells was reduced to 26% of that observed initially when cells were reacted a second time with fresh substrate mixture. The stability (reuseability) of Phenylalanine Ammonia-Lyase (PAL) containing cells was significantly influenced by both the trans-cinnamate concentration and initial reaction pH. Using 2% t-cinnamate, l-phenylalanine production was 7-fold greater after 3 successive runs at pH 9.0 than at the optimum of pH 10.2. Cells reacted in the presence of 5% t-cinnamate were relatively unstable. Permeabilising agents, such as toluene and xylene, stimulated l-phenylalanine production but also enhanced instability of the catalyst. Several effectors were shown to stimulate the initial rate of the PAL bioconversion, but only sorbitol, alginate, glutaraldehyde, polyethylene glycol and glycerol conferred any significant degree of stability. Sparging of cultures and bioreactors with various gases revealed that oxygen enhanced PAL inactivation, CO₂ had little effect and nitrogen conferred remarkable stability on PAL activity for several weeks in culture medium. The presence of chloride ions (from HCl) and aeration of substrate mixtures resulted in poor reuseability of catalyst. A combination of H₂SO₄ substitution for HCl and N₂-sparging resulted in excellent initial conversions and good catalyst stability at 26°C but less at 30°C. The inclusion of 1.5 M sorbitol in reaction mixtures maintained PAL stability over several successive incubations.     

Recent advances in chemiluminescence-based immunoassays for steroid hormones

Several formats of solid-phase separation techniques for the measurement of steroids and urinary steroid conjugates using chemiluminescence as an end point are described. These formats include: (1) immunoadsorption of second antibodies directed against the first antibody on solid support; (2) specific immunoadsorbents consisting of primary antibodies covalently coupled to polymer beads; (3) second antibody coupled to a polymer containing magnetic particles. In these assays a steroid-chemiluminescent marker conjugate serves as the labelled ligand, and highly specific homologous monoclonal antibodies are used to provide optimal specificity and rigorous standardization. These techniques enabled the direct measurement of steroid glucuronides in diluted urine and of steroids in plasma.     

Effect of bacterial growth-inhibiting ingredients on the Ames mutagenicity of medicinal herbs

A solvent fractionation method was introduced to screen for mutagenicity in 10 medicinal herbs being consumed in Korea. The Ames mutagenicity test result of Scutellariae and Rhei was significantly increased by eliminating growth-inhibiting substances through solvent fractionation of the crude extract. It is suggested that a physicochemical pretreatment should reduce the false-negative results which are caused by the presence of growth-inhibiting substances in complex mixtures.     

Characterization of the Stimulation of Ethylene Production by Galactose in Tomato (Lycopersicon esculentum Mill.) Fruit

We have characterized the stimulation of ethylene production by galactose in tomatoes (Lycopersicon esculentum Mill.). The effect of concentration was studied by infiltrating 0, 4, 40, 100, 200, 400, or 800 micrograms galactose for each gram of fresh fruit weight into mature green `Rutgers' fruit. Both 400 and 800 micrograms per gram fresh weight consistently stimulated a transient increase in ethylene approximately 25 hours after infiltration; the lower concentrations did not. Carbon dioxide evolution of fruit infiltrated with 400 to 800 micrograms per gram fresh weight was greater than that of lower concentrations. The ripening mutants, rin and nor, also showed the transient increase in ethylene and elevated CO₂ evolution by 400 micrograms per gram fresh weight galactose. 1-Aminocyclopropane-1-carboxylic acid (ACC) content and ACC-synthase activity increased concurrently with ethylene production. However, galactose did not stimulate ACC-synthase activity in vitro. The infiltrated galactose in pericarp tissue was rapidly metabolized, decreasing to endogenous levels within 50 hours. Infiltrated galacturonic acid, dulcitol, and mannose stimulated transient increases in ethylene production similar to that of galactose. The following sugars produced no response: sucrose, fructose, glucose, rhamnose, arabinose, xylose, raffinose, lactose, and sorbitol.     

Effect of GA3 on the Cyclic AMP Biosynthesis in Maize Seedling

The effect of GA₃ on the biosynthesis of cAMP was studied toinvestigate the mechanism of gibberellic acid action. The presenceof cAMP in germinating maize seedlings was confirmed. The concentrationgradient of cAMP in maize seedlings inclined from shoot apexto root. The amount of cAMP in maize shoot was increased about3.3 times by exogenous GA₃. These results indicate that thebiosynthesis of cAMP is stimulated by GA₃. (Received June 17, 1986; Accepted January 22, 1987)     

Dynamics of populations with changing rates: generalization of the stable population theory

A general and complete exposition of the dynamics of populations with changing vital rates is given in the discrete time formulation. Results obtained are stronger than Lopez's or Hajnal's. In addition to the proof of existence of limits, an explicit expression for the age distribution is obtained by considering forward products of population projection matrices, while an explicit expression for the generalized reproductive values is obtained by considering backward products. The forward and backward characteristic equations respectively determine the forward and backward growth rates. The relative age distribution is compared to the alternative expression of Y.J. Kim (1986, Demography 23 (3), 451-461), which is the discrete version of S.H. Preston and A.J. Coale (1982, Pop. Index 48 (2), 217-259).     

Molecular cloning and differential expression of somatic and testis-specific H2B histone genes during rat spermatogenesis

We have cloned cDNA of a testis-specific histone, TH2B (a variant of H2B), and rat somatic H2B gene to investigate regulation of testis-specific histone genes during rat spermatogenesis. The amino acid sequences deduced from DNA sequences show extensive sequence divergence in the N-terminal third of the two histones. The rest is highly conserved. One cysteine residue was found in TH2B. No cysteine is present in somatic histones except in H3 histone. We investigated the expression of TH2B and H2B genes using the regions of sequence divergence as hybridization probes. The TH2B gene is expressed only in the testis, and the expression of this gene is detected 14 days after birth, reaching a maximum at Day 20. The level of H2B mRNA shows a reciprocal pattern. This contrasting pattern can be explained by the gradually changing proportion of spermatogonia and spermatocytes with testicular maturation. In situ cytohybridization studies show that H2B gene is expressed primarily in proliferating spermatogonia and preleptotene spermatocytes, whereas TH2B gene is expressed exclusively in pachytene spermatocytes which first appear in testis about 14 days after birth. H2B and TH2B genes appear to be ideal markers for the study of proliferation and differentiation events in spermatogenesis and their regulatory mechanisms.     

Recalibration of the Pseudomonas aeruginosa Strain Pao Chromosome Map in Time Units Using High-Frequency-of-Recombination Donors

High-frequency-of-recombination donors of P. aeruginosa strain PAO were generated using a temperature-sensitive, replication mutant of the IncP-1 plasmid R68, loaded with the transposon Tn2521. Fourteen donors so isolated mobilized the chromosome in a polarized manner from a number of different transfer origins. The donors were used to construct a time of entry map of the entire chromosome and this was achieved by determining the time of entry of 32 randomly dispersed markers in crosses using nalidixic acid to interrupt chromosome transfer. Analysis of the time of entry data enabled the recalibration of the chromosome map to 75 min.     

The nifA gene of Rhizobium meliloti is oxygen regulated.

Experiments using plasmid-borne gene fusions and direct RNA measurements have revealed that expression from the nifA gene is induced in Rhizobium meliloti when the external oxygen concentration is reduced to microaerobic levels. Induction occurs in the absence of alfalfa and in the presence of fixed nitrogen and does not require ntrC. The production of functional nifA gene product (NifA) can be demonstrated by its ability to activate the nitrogenase promoter P1. Aerobic induction of nifA can also occur during nitrogen starvation at low pH, but in this case induction is dependent on ntrC and does not lead to P1 activation. The data indicate that reduced oxygen tension is potentially a major trigger for symbiotic activation of nitrogen fixation in Rhizobium species.