A virtual-pinhole PET device for improving contrast recovery and enhancing lesion detectability of a one-meter-long PET scanner: a simulation study.

This paper presents a simulation study to demonstrate that the contrast recovery coefficients (CRC) and detectability of small lesions of a one-meter-long positron emission tomography (PET) scanner can be further enhanced by the integration of high resolution virtual-pinhole (VP) PET devices. The scanner under investigation is a Siemens Biograph Vision Quadra which has an axial field-of-view (FOV) of 106 cm. The VP-PET devices contain two high-resolution flat panel detectors, each composed of 2 × 8 detector modules each of which consists of 32 × 64 lutetium-oxyorthosilicate crystals (1.0 × 1.0 × 10.0 mm3each). Two configurations for the VP-PET device placement were evaluated: (1) place the two flat-panel detectors at the center of the scanner's axial FOV below the patient bed; (2) place one flat-panel detector at the center of the first and the last quarter of the scanner's axial FOV below the patient bed. Sensitivity profiles were measured by moving a point22Na source stepwise across the scanner's FOV axially at different locations. To assess the improvement in CRC and lesion detectability by the VP-PET devices, an elliptical torso phantom (31.6 × 22.8 × 106 cm3) was first imaged by the native scanner then subsequently by the two VP-PET geometry configurations. Spherical lesions (4 mm in diameter) having 5:1 lesion-to-background radioactivity concentration ratio were grouped and placed at nine regions in the phantom to analyze the dependence of the improvement in plane. Average CRCs and their standard deviations of the 7 tumors in each group were computed and the receiver operating characteristic (ROC) curves were drawn to evaluate the improvement in lesion detectability by the VP-PET device over the native long axial PET scanner. The fraction of coincidence events between the inserts and the scanner detectors was 13%-16% (out of the total number of coincidences) for VP-PET configuration 1 and 2, respectively. The VP-PET systems provide higher CRCs for lesions in all regions in the torso, with more significant enhancement at regions closer to the inserts, than the native scanner does. For any given false positive fraction, the VP-PET systems offer higher true positive fraction compared to the native scanner. This work provides a potential solution to further enhance the image resolution of a long axial FOV PET scanner to maximize its lesion detectability afforded by its super high effective sensitivity.

Development of an Innovative Process for High-Temperature Fruit Juice Extraction Using a Novel Thermophilic Endo-Polygalacturonase From Penicillium oxalicum.

Efficient and cost-effective production of thermophilic endo-polygalacturonase is desirable for industrial fruit juice production, because its application could shorten the processing time and lower the production cost, by eliminating the separate step of pectin degradation. However, no endo-polygalacturonase that both functions well at sufficiently high temperature and can be manufactured economically, has been reported previously. In this study, the cDNA encoding a thermophilic endo-polygalacturonase from Penicillium oxalicum CZ1028, was cloned and over-expressed in Pichia pastoris GS115 and Escherichia coli BL21(DE3). The recombinant proteins PoxaEnPG28B-Pp (from P. pastoris) and PoxaEnPG28B-Ec (from E. coli) were isolated and purified. PoxaEnPG28B-Pp was sufficiently thermostable for potential industrial use, but PoxaEnPG28B-Ec was not. The optimal pH and temperature of PoxaEnPG28B-Pp were pH 5.0 and 65°C, respectively. The enzyme had a low K m of 1.82 g/L and a high V max of 77882.2 U/mg, with polygalacturonic acid (PGA) as substrate. The performance of PoxaEnPG28B-Pp in depectinization of papaya, plantain and banana juices at 65°C for 15 min was superior to that of a reported mesophilic endo-polygalacturonase. PoxaEnPG28B-Pp is the first endo-polygalacturonase reported to show excellent performance at high temperature. An innovative process, including a step of simultaneous heat-treatment and depectinization of fruit pulps with PoxaEnPG28B-Pp, is reported for the first time.

Identification of an acidic endo-polygalacturonase from Penicillium oxalicum CZ1028 and its broad use in major tropical and subtropical fruit juices production.

Endo-polygalacturonases play an important role on depectinization in fruit juices industry. A putative endo-polygalacturonase gene PoxaEnPG28A was cloned from Penicillium oxalicum CZ1028. PoxaEnPG28A consisted of a putative signal peptide and a catalytic domain belonging to glycoside hydrolase family 28, and it shared 72% identity with that of a functionally characterized endo-polygalacturonase from Trichoderma harzianum. Gene PoxaEnPG28A was successfully expressed in Pichia pastoris with a high yield of 1828.7 U/mL. The purified recombinant enzyme PoxaEnPG28A hydrolyzed polygalacturonic acid in endo-manner releasing oligo-galacturonates. PoxaEnPG28A showed maximal activity at pH 5.5 and 55°C, and was stable between pH 3.0 to 10.0 and below 45°C. The kinetic constants Km and Vmax of PoxaEnPG28A were calculated as 1.57 g/L and 14,641.29 U/mg, respectively. PoxaEnPG28A significantly improved the yields of fruit juices from banana, plantain, papaya, pitaya and mango. The high production level of the recombinant enzyme PoxaEnPG28A by P. pastoris and remarkable catalytic activity of PoxaEnPG28A toward five kinds of fruit juices made the enzyme a potential application in agriculture and food industries.

Cloning, expression, and characterization of coenzyme-B12-dependent diol dehydratase from Lactobacillus diolivorans.

The three gldCDE genes from Lactobacillus diolivorans, that encode the three subunits of the glycerol dehydratase, were cloned and the proteins were co-expressed in soluble form in Escherichia coli with added sorbitol and betaine hydrochloride. The purified enzyme exists as a heterohexamer (α2ß2γ2) structure with a native molecular mass of 210 kDa. It requires coenzyme B12 for catalytic activity and is subject to suicide inactivation by glycerol during catalysis. The enzyme had maximum activity at pH 8.6 and 37 °C. The apparent K m values for coenzyme B12, 1,2-ethanediol, 1,2-propanediol, and glycerol were 1.5 µM, 10.5 mM, 1.3 mM, and 5.8 mM, respectively. Together, these results indicated that the three genes gldCDE encoding the proteins make up a coenzyme B12-dependent diol dehydratase and not a glycerol dehydratase.

Saturation-mutagenesis in two positions distant from active site of a Klebsiella pneumoniae glycerol dehydratase identifies some highly active mutants.

Synthesis of 1,3-propanediol (1,3-PD) from glycerol through the biotransformation process requires two steps, catalyzed by glycerol dehydratase (GDHt) and 1,3-PD oxidoreductase. GDHt is the rate-limiting enzyme in this process. All recombinant microorganisms for production of 1,3-PD so far utilized the natural genes that may not have been optimized. Two positions, which are 19.3A and 29.6A away from the active site in GDHt from Klebsiella pneumoniae, were subjected to saturation-mutagenesis and 38 mutants were characterized. The catalytic activity of a mutant in beta-subunit (beta-Q42F, 29.6A from the active site) was 8.3-fold higher than the wild type, and the enzyme efficiency of other two mutants beta-Q42L and beta-Q42S for substrate glycerol was 336-fold and 80-fold higher than that for 1,2-propanediol. This investigation supplied further evidence that distant mutations could be a good source of diversity and therefore, made a contribution to the toolbox of industrial enzyme improvement.