Benzaldehyde lyase, a novel thiamine PPi-requiring enzyme, from Pseudomonas fluorescens biovar I.

Pseudomonas fluorescens biovar I can grow on benzoin as the sole carbon and energy source. This ability is due to benzaldehyde lyase, a new type of enzyme that irreversibly cleaves the acyloin linkage of benzoin, producing two molecules of benzaldehyde. Benzaldehyde lyase was purified 70-fold and found to require catalytic amounts of thiamine PPi (TPP) and a divalent cation as cofactors. Optimal activity was obtained with a 1.0 mM concentration of Mn2+, Mg2+, or Ca2+. Gel permeation chromatography indicated a native molecular weight of 80,000, whereas the enzyme migrated in sodium dodecyl sulfate-containing polyacrylamide gels as a single polypeptide with a molecular weight of 53,000. Benzaldehyde lyase is highly specific; of a variety of structurally related compounds tested, only benzoin and anisoin (4,4'-dimethoxybenzoin) acted as substrates, their apparent Kms being 9.0 x 10(-3) and 3.25 x 10(-2) mM, respectively. A catalytic mechanism for the enzyme is proposed.     

Subcellular localization of the major pneumococcal autolysin: a peculiar mechanism of secretion in Escherichia coli

The major pneumococcal autolysin (N-acetylmuramoyl-L-alanine amidase) has been localized in the cellular envelope of Streptococcus pneumoniae and Escherichia coli by using immunocytochemical labeling on ultrathin sections and whole-mounted cells. Cell fractionation experiments in E. coli confirmed the peripheral localization of the pneumococcal amidase and suggested that this enzyme is weakly bound to the outer face of the cytoplasmic membrane. This interaction does not depend on the presence of choline but represents an intrinsic property of the amidase. The autolysin, that is synthesized without any N-terminal signal sequence (García, P., García, J. L., García, E., and López, R. (1986) Gene (Amst.) 43, 265-272) was not processed during translocation. A new regulatory mechanism that might be specific for bacterial autolysins is discussed.     

Monotherapy with acebutolol in hypertensive diabetic patients

Monotherapy of hypertension with acebutolol in diabetics in daily dose of 200-400 mg for 6 weeks induced only non-significant and practically not acceptable hypotensive effect in groups of patients with hypertension and diabetes type I or type II without nephropathy. No therapeutical effect was observed in hypertension in diabetics type I with nephropathy. Administration of acebutolol to hypertensive diabetic patients with nephropathy resulted in tendency to increase in albuminuria. Values of creatinine clearance did not change at the same time. Also no effect of acebutolol on glycemic or lipid indices was observed. The lack of clear hypotensive effect under studied conditions of acebutolol in diabetic patients contrasted with its significant action in comparative group of hypertensive non-diabetic subjects.     

Somatostatin binding to dissociated cells from rat cerebral cortex

A method has been developed for the study of somatostatin (SS) binding to dissociated cells from rat cerebral cortex. Binding of [¹²⁵I][Tyr¹¹]SS to cells obtained by mechanical dissociation of rat cerebral cortex was dependent on time and temperature, saturable, reversible and highly specific. Under conditions of equilibrium, i.e., 60 min at 25°C, native SS inhibited tracer binding in a dose-dependent manner. The Scatchard analysis of binding data was linear and yielded a dissociation constant of 0.60±0.08 nM with a maximal binding capacity of 160±16 fmol/mg protein. The binding of [¹²⁵I][Tyr¹¹]SS was specific as shown in experiments on tracer displacement by the native peptide, SS analogues, and unrelated peptides.     

An extended x-ray absorption fine structure study of the high-affinity cation-binding site in the purple membrane.

The structure of the high-affinity cation-binding site of bacteriorhodopsin was studied using extended x-ray absorption fine structure techniques. The results obtained for Mn2+ in aqueous solution and for the complex BR-Mn2+ (1:1 molar ratio) show great similarities, suggesting that Mn2+, when bound to this site, is coordinated with six atoms of oxygen, forming an octahedral disposition. The interatomic distance between the atoms of oxygen and the Mn2+ was found to be 2.17 A for the complex BR-Mn2+, similar to Mn2+ in solution (2.15 A). In addition, the absence of any other peak at greater distances in the Fourier-transformed spectrum indicates that neither phosphorus nor sulphur atoms are present in the second coordination shell. This suggests that this binding site is located in the protein, discarding the proximity of lipid polar headgroups.     

Dialysable leukocyte extracts modify the course of experimental paracoccidioidomycosis in the Syrian hamster

The effect of dialysable leukocyte extracts (DLE) obtained from hamsters immunized withParacoccidioides brasiliensis (immune DLE) and from non-immunized hamsters (non-immune DLE) was studied in hamsters inoculated withP. brasiliensis by the intratesticular route. Treatment with immune or non-immune DLE was started during the third week of infection and was repeated at 7, 11, 15 and 19 weeks. A group of untreated infected animals was used as control. Animals were submitted to the delayed hypersensitivity skin test toP. brasiliensis antigen (PbAg) in vivo and assayed in vitro by the macrophage migration inhibition test in the presence of Phytohemagglutinin (PHA) and PbAg and by immunodiffusion for specific antibody. The animals were sacrificed at 4, 8, 12, 16 and 20 weeks. The morphology and extension of the lesions were studied at the inoculation site, and in lymph nodes, lungs, liver, spleen and kidneys. In contrast to the controls, animals treated with both DLEs maintained a positive cell-mediated immune response throughout the experiment and developed less extensive infection with a significantly lower number of fungi in the lesions. The results suggest that immune and non-immune DLE preparations modified the evolution of experimental paracoccidioidomycosis with equal efficiency. This similarity may be explained by the immunoregulatory activities of both extracts.     

The protective effect of arbutin against potassium bromate-induced oxidative damage in the rat brain

This study aimed to investigate the protective effects of arbutin (ARB) against brain injury induced in rats with potassium bromate (KBrO₃). The rats were divided into four groups as Group 1: Control (0.9% NaCl ml/kg/day p.), Group 2: KBrO₃ (100 mg/kg (gavage), Group 3: ARB (50 mg/kg/day p.), and Group 4: KBrO₃ + ARB (100 mg/kg (gavage) + 50 mg/kg/day p.). At the end of the fifth day of the study, the rats in all groups were killed, and their brain tissues were collected. In the collected brain tissues, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) levels were measured, and routine histopathological examinations were made. The MDA levels in the group that was exposed to KBrO₃ were significantly higher than those in the control group (p ˂ 0.001). In comparison to the KBrO₃ group, the MDA levels in the KBrO₃ + ARB group were significantly lower (p ˂ 0.001). It was observed that SOD and CAT enzyme activity levels were significantly lower in the KBrO₃ group compared to the control group (p ˂ 0.001), while these levels were significantly higher in the KBrO₃ + ARB group than in the KBrO₃ group (p ˂ 0.001). Additionally, the group that was subjected to KBrO₃ toxicity, as well as ARB administration, had much lower levels of histopathologic signs than the group that was subjected to KBrO₃ toxicity only. Consequently, it was found that KBrO₃ exposure led to injury in the brain tissues of the rats, and using ARB was effective in preventing this injury.