Role of cysteine residues in glutathione synthetase from Escherichia coli B. Chemical modification and oligonucleotide site-directed mutagenesis

Escherichia coli B glutathione synthetase is composed of four identical subunits; each subunit contains 4 cysteine residues (Cys-122, -195, -222, and -289). We constructed seven different mutant enzymes containing 3, 2, or no cysteine residues/subunit by replacement of cysteine codons with those of alanine in the gsh II gene using site-directed mutagenesis. Three mutant enzymes, Ala289, Ala222/289, Cys-free (Ala122/195/222/289), in which cysteine at residue 289 was replaced with alanine, were not inactivated by 5,5'-dithiobis(2-nitrobenzoate) (DTNB), while the other four mutants retaining Cys-289 were inactivated at the wild-type rate. From these selective inactivations of mutant enzymes by DTNB, the sulfhydryl group modified by DTNB was unambiguously identified as Cys-289. In this way, Cys-289 was found to be also a target of modification with 2-nitrothiocyanobenzoate and N-ethylmaleimide, while Cys-195 was of p-chloromercuribenzoate. These results suggest that both Cys-195 and Cys-289 were not essential for the activity of the glutathione synthetase, but chemical modification of either one of the two sulfhydryl groups resulted in complete loss of the activity. Replacement of Cys-122 to Ala-122 enhanced the reactivity of Cys-289 with sulfhydryl reagents.

[The availability of digital subtraction angiography using continuous intra-arterial infusion tubes founded various malignancy]

DSA was employed using continuous intraarterial infusion tubes for various malignancies (73 cases) which were examined a total of 135 times. In head and neck malignancy (50 cases), the general position of the infusion tube had been determined beforehand by dye infusion, but DSA from the tube showed that the tubes in 24 cases (48%) were located in the wrong position, especially in tongue cancer (21 cases) where many tubes were discovered to be in an erroneous position (71%) such as the common carotid artery. We were unable to determine the effect of chemotherapy and radiation using DSA only. In 9 cases of breast cancer for which fixation of the tube was not attempted under X-ray fluoroscopy, 7 (78%) showed an unusual tube position such as the intraaortic arch. In 5 cases of abdominal malignancy, only the tube position for sigmoid colon cancer was unusual. We were able to observe the effect of chemotherapy by DSA in 2 cases. For DSA in one out of 3 hepatomas using a Port-A-Cath, we observed that infusion of anticancer drug with degradable starch microspheres caused a reduction in tumor size. However, in the two remaining cases, we were unable to observe any effect of infusion of these drugs by DSA for various mechanical reasons. DSA from an infusion tube revealed not only the location of the tube accurately and promptly, but also the effect of chemotherapy.

Homology of Escherichia coli B glutathione synthetase with dihydrofolate reductase in amino acid sequence and substrate binding site

Glutathione synthetase from Escherichia coli B showed amino acid sequence homology with mammalian and bacterial dihydrofolate reductases over 40 residues, although these two enzymes are different in their reaction mechanisms and ligand requirements. The effects of ligands of dihydrofolate reductase on the reaction of E. coli B glutathione synthetase were examined to find resemblances in catalytic function to dihydrofolate reductase. The E. coli B enzyme was potently inhibited by 7,8-dihydrofolate, methotrexate, and trimethoprim. Methotrexate was studied in detail and proved to bind to an ATP binding site of the E. coli B enzyme with K1 value of 0.1 mM. The homologous portion of the amino acid sequence in dihydrofolate reductases, which corresponds to the portion coded by exon 3 of mammalian dihydrofolate reductase genes, provided a binding site of the adenosine diphosphate moiety of NADPH in the crystal structure of dihydrofolate reductase. These analyses would indicate that the homologous portion of the amino acid sequence of the E. coli B enzyme provides the ATP binding site. This report gives experimental evidence that amino acid sequences related by sequence homology conserve functional similarity even in enzymes which differ in their catalytic mechanisms.

Pituitary dwarfism: CT evaluation of the pituitary gland

The pituitary glands of 12 patients, aged 4-20 years, with pituitary dwarfism and of 15 age-matched control patients were evaluated with contrast-enhanced, high-resolution computed tomography (CT). In control patients, CT clearly demonstrated pituitary glands and stalks, 2.5-9.0 mm in height (average, 5.7 mm +/- 1.8). In the 12 patients with pituitary dwarfism, CT did not demonstrate the gland or stalk in four; CT faintly showed only the stalk in another four and showed a small gland (less than 2 mm in height) and a small to normal stalk in the remaining four. Eleven of the 12 patients had a birth history of breech presentation. Possible causes of pituitary dwarfism are discussed.

Thin section CT of normal pituitary glands

In order to better understand the CT appearance of the normal pituitary gland, we scrutinized the pituitary glands of 55 patients who had no clinical indication of pituitary abnormality. The superior surface of the pituitary gland was convex in 9 cases (16.4%), flat in 16 (29.1%), and concave in 30 (54.5%). All but one of the glands with upward convexity belonged to patients less than 40 years old. The height of the pituitary glands was from 2 mm to 7 mm in 48 (87.3%) and 7 mm to 9.1 mm in 7 (12.7%); all but one case was less than 40 years old. Although earlier reports have suggested the presence of a pituitary microadenoma when the gland has a convexity of its superior surface or is more than 7 mm in height, these findings can be seen in normal pituitary glands, particularly in younger individuals. Therefore, pituitary microadenoma should be diagnosed carefully in younger patients. The low density area frequently seen in the superior aspect of pituitary glands on axial scans was found to result from the concave superior surface of the gland. The pituitary stalk was off the midline in five patients (9%). Shifting of the pituitary stalk can be seen in the normal pituitary gland and is not always characteristic of microadenoma.

Dynamic CT scanning for the evaluation of pituitary tumor invasion to the cavernous sinus

A CT method for evaluating cavernous sinus invasion by pituitary adenomas or parasellar tumors is described. This technique is easily performed without special software. A persistent, isolated visualization of the internal carotid artery seems to indicate invasion of the cavernous sinus.

Serial determinations of serum enzymes following aorta-coronary bypass surgery and acute myocardial infarction

Serial determinations of serum creatine kinase (CK), cardio-specific isoenzyme of CK (CK-MB), glutamic oxaloacetic transaminase (GOT) and alpha-hydroxybutylate dehydrogenase (HBD) were made in 29 consecutive patients undergoing aorta-coronary (AC) bypass grafting, and the results were compared with those in 31 patients with acute myocardial infarction (AMI). Postoperatively, all patients had an uneventful postoperative course and there was no evidence of AMI. The time course of enzyme activity following surgery was characterized by 1) shortening of peak activity time of all enzymes except CK, 2) rapid disappearance of CK-MB, 3) prolonged normalization of GOT and HBD. Peak activities of CK, CK-MB, GOT and HBD in AC bypass patients were 801 +/- 77, 46 +/- 6, 100 +/- 9 and 718 +/- 32 IU (mean +/- SEM), respectively, which were equivalent to 46%, 12%, 22% and 47% of those in AMI. The degree of postoperative CK-MB elevation was influenced by the duration of the operation and the extracorporeal circulation, and the number of grafts bypassed. The peak CK-MB activity did not correlate with the CK peak. The ratio of CK-MB to CK was much smaller in AC bypass than in AMI (6.5 +/- 1.8 vs. 20.1 +/- 1.4%). It was concluded that serum enzyme elevations after AC bypass surgery largely reflected enzyme release from the skeletal muscle rather than the myocardium.

[Computed tomography in brain metastases (author's transl)]

CT scan of the one hundred and sixteen metastatic brain tumors in 50 patients was reviewed and compared to the previous reports. The most common primary organ was lung (43%) followed by breast (18%), colon (10%) and kidney (6%). Solitary nodule was found in 20 patients (40%). On plain CT scan, tumor nodules were demonstrated as slightly high density in 38 (33%), isodensity in 50 (43%) and slightly low density in 28 (24%). Majority of tumor nodules were present in the corticomedullary junction (82%). Brain edema seen as a peritumoral low density was extensive in comparison with the edema in the glioma of the similar size. On contrast CT scan, ring like enhancement was seen in 41 (35%). Intra-tumoral bleeding was shown in 2 metastatic nodules from choriocarcinoma and in one metastatic nodule from renal cell carcinoma. All 3 cases were proved by surgery or autopsy.

[Thin-section CT scan of the pituitary gland (author's transl)]

Topographic anatomy of the pituitary fossa was studied by 2 mm thin-section CT scan (Somatom II). Nineteen with normal pituitary (control group) and 20 with suspected pituitary abnormality were selected. Plain and contrast CT were performed in all cases. Contrast CT was carried out immediately after the rapid infusion of 220 ml of 30% iodinated contrast medium. In all of control group but two, pituitary gland was detected as homogenous density and its density was as same as density of normal brain tissues, and was enhanced in degree of about 25 CT number. In 2 cases, small low density was visualized in the pituitary gland. Pituitary gland was differentiated from cavernous sinus was usually higher than the pituitary gland. In abnormal group, the microadenoma of the pituitary gland was diagnosed in 5 cases and 3 out of 5 cases was proved by surgery. All 3 microadenomas proved slightly dense by plain CT and enhanced higher than normal pituitary gland by contrast CT. Polytomograms showed no abnormality of the sella turcica in one of these 3 cases. Although 3 microadenomas were detected by the abnormal enhancement, we are not sure whether all of microadenoma can be detected by CT alone. Arachnoid herniation into the pituitary fossa was diagnosed in 7 of control group and 2 of abnormal group. Four out of these 9 cases were verified by using Metrizamide CT. By plain thin-section CT, the diagnosis of arachnoid herniation seems to be possible without Metrizamide CT.