Formation of the thioester, N-acetyl, S-lactoylcysteine, by reaction of N-acetylcysteine with pyruvaldehyde in aqueous solution.
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Acetylcysteine↗
Biomedical subjects
A L Weber
Publications and source records attributed to A L Weber.
Formation of pyrophosphate on hydroxyapatite with thioesters as condensing agents.
"Energy-rich" thioesters are shown to act as condensing agents in the formation of pyrophosphate on hydroxyapatite in the presence of water at ambient temperature. The yield of pyrophosphate based on thioester ranges from 2.5% to 11.4% and depends upon the pH and concentration of reactants. Reaction of 0.130 M hydroxyapatite suspended in a solution of 0.08 M sodium phosphate and 0.20 M imidazole hydrochloride (pH 7.0) with 0.10 M N,S-diacetylcysteamine for 6 days gives the highest yield of pyrophosphate (11.4%). Pyrophosphate formation requires the presence of hydroxyapatite, sodium phosphate and the thioester, N,S-diacetylcysteamine. The related thioester, N,S-diacetylcysteine, also yields pyrophosphate in reactions on hydroxyapatite.
Diphosphates↗
Pathways of orbital extension of extraorbital neoplasms.
Orbital involvement was demonstrated by computed tomography in 53 patients with neoplasms of the head and neck. The pathway of extension into the orbit depended on the histology and location of the tumor. Tumors of the paranasal sinuses and face usually extended through the medial wall, floor, anterior orbit, or the inferior orbital fissure. Intracranial lesions most commonly extended through the posterior lateral wall, but the superior orbital fissure and optic canal were also pathways for orbital extension.
Head and Neck Neoplasms↗
Another look at blow-out fractures of the orbit.
Thirty cases of orbital floor blow-out fractures proven by tomography were retrospectively reviewed to determine the accuracy of the plain films. Using the maximum diameter from the tomograms, the area and volume of the fractures were calculated and correlated with the presence of diplopia and enophthalmos at the time of presentation and at subsequent follow-up. Nine of the 30 cases underwent surgical repair. Orbital floor fractures were recognized in 29 of 30 cases using only the 28 degrees Caldwell and Waters views. Routine tomography is unnecessary and should be reserved as a preoperative evaluation in patients with enophthalmos to establish the presence of a significant associated medial wall prolapse.
Adolescent↗
Evaluation of orbital and eye lesions by radiographic examination, ultrasound, and computerized tomography.
This article examines three imaging procedures for the evaluation of orbital and eye lesions. In the radiographic section we discuss the normal anatomy, the projections to show the anatomy, and the interpretation of bone changes caused by benign and malignant lesions. In the next section we describe the equipment employed in the ultrasonic evaluation of the eye and orbit and the principles applied in the diagnosis of lesions of the eye and orbit by ultrasound. We introduce the CT section by explaining the methodology of computerized tomography of the orbit. The criteria for evaluating lesions of the eye and orbit are presented with appropriate cases for illustration. The discussion and summary detail the relative merit of these imaging procedures ad their usefulness in the diagnosis work-up of pathological conditions of the eye and orbit.
Adult↗
Parasellar chondrosarcoma in a patient with Ollier's disease.
Cartilaginous intracranial neoplasms are rare and are located most commonly at the base of the skull in the parasellar region. They may occur with similar lesions in the rest of the skeleton (Ollier's disease) or present with multiple enchondromas and soft tissue hemangiomas (Maffuci's syndrome).
Adolescent↗
Formation of the thioester, N,S-diacetylcysteine, from acetaldehyde and N,N'diacetylcystine in aqueous solution with ultraviolet light.
The thioester, N,S-diacetylcysteine, is formed during the illumination of phosphate buffered (pH 7.0) aqueous solutions of acetaldehyde and N,N'-diacetylcystine with ultraviolet light. The yield of N,S-diacetylcysteine relative to N-acetylcysteine and unidentified products progressively increases as ultraviolet light below 239 nm, 253 nm and 281 nm is cut off with optical filters. When ultraviolet light below 320 nm is removed with an optical filter, there is no detectable reaction. Illumination of 0.025 M N,N'-diacetylcystine with 0.5 M and 1.0 M acetaldehyde with filtered ultraviolet light gives, respectively, 20% and 80% yields of N,S-diacetylcysteine. In the reaction with 1.0 M acetaldehyde, N-acetylcysteine forms early in the reaction and later decreases with its conversion to N,S-diacetylcysteine. The prebiotic significance of these reactions is discussed.
Acetaldehyde↗
Formation of pyrophosphate, tripolyphosphate, and phosphorylimidazole with the thioester, n, s-diacetyl-cysteamine, as the condensing agent.
Reaction of 0.20M orthophosphate with 0.20M N,S-diacetylcysteamine in 0.40M imidazole at pH 7.0 or 8.0 under drying conditions at 50 degree C for 6 days yields pyrophosphate and tripolyphosphate in the presence and absence of 0.10M divalent metal ion. The efficiency of utilization of N,S-diacetylcysteamine in the formation of pyrophosphate linkages ranges from 3 - 8% under the above conditions. The thioester, N,S-diacetylcysteamine, and imidazole are required for phosphoanhydride formation. Reaction of 0.40M orthophosphate with 0.20M N,S-diacetylcysteamine in 0.40M orthophosphate with 0.20M N,S-diacetylcysteamine in 0.40M imidazole at ambient temperature for 6 days yields phosphorylimidazole in the absence or presence of 0.50M MgCl2. Phosphorylimidazole and pyrophosphate are formed in the presence of 0.05M CaCl2; pyrophosphate and tripolyphosphate are formed with 0.15M CaCl2. The efficiency of utilization of N,S-diacetylcysteamine in the formation of pyrophosphate linkages is roughly 7% at 6 days of reaction with 0.15M CaCl2. The thioester, N,S-diacetylcysteamine and imidazole are required for the formation of phosphoanhydrides. The significance of these reactions to molecular evolution is discussed.
Biological Evolution↗
The effect of poly(C) on the formation of peptide bones from the 2'(3')-glycyl ester of a guanosine nucleotide.
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Chemical Phenomena↗
Reasons for the occurrence of the twenty coded protein amino acids.
Factors involved in the selection of the 20 protein L-alpha-amino acids during chemical evolution and the early stages of Darwinian evolution are discussed. The selection is considered on the basis of the availability in the primitive ocean, function in proteins, the stability of the amino acid and its peptides, stability to racemization, and stability on the transfer RNA. We conclude that aspartic acid, glutamic acid, arginine, lysine, serine and possibly threonine are the best choices for acidic, basic and hydroxy amino acids. The hydrophobic amino acids are reasonable choices, except for the puzzling absences of alpha-amino-n-butyric acid, norvaline and norleucine. The choices of the sulfur and aromatic amino acids seem reasonable, but are not compelling. Asparagine and glutamine are apparently not primitive. If life were to arise on another planet, we would expect that the catalysts would be poly-alpha-amino acids and that about 75% of the amino acids would be the same as on the earth.
Amino Acids↗
Cartilaginous tumors of the larynx.
Laryngeal cartilaginous tumors are well-defined masses that arise within the endolaryngeal structures, predominantly the cricoid cartilage. Twelve cases with long-term followup are reviewed. The importance of early and complete radiological evaluation and the potential for recurrence is emphasized. Since metastases or extralaryngeal extension is rare, conservative surgery, preserving laryngeal function as long as possible, is the treatment of choice. The histological distinction of chondroma versus chondrosarcoma is not essential for the clinical management of these lesions, and we suggest they be designated as cartilaginous tumors of the larynx.
Adolescent↗
Poly(U)-directed peptide-bond formation from the 2'(3')-glycyl esters of adenosine derivatives.
The self-condensation of 2'(3')-O-glycyl esters of adenosine, adenosine-5'-(O-methylphosphate) and P1, P2-diadenosine-5'-pyrophosphate in 6.2 mM solutions at pH 8.0 and -5 degrees C in the presence of 12.5 mM poly(U) yields approximately 3 times as much diketopiperazine as reactions without poly(U). As the concentration of 2'(3')-O-(glycyl)-P1, P2-diadenosine-5'-pyrophosphate is decreased from 6.2 mM to 1.5 mM the yield of diketopiperazine in the presence of poly(U) decreases slightly from 6.6% to 5.2%, whereas, in the absence of poly(U) the yield of diketopiperazine decreases substantially from 2.4% to 0.75%. The enhanced yield of diketopiperazine that is attributed to the template action of poly(U) is temperature dependent and is observed only at temperatures below 10 degrees C (5 degrees C to -5 degrees C) for 6.2 mM 2'(3')-O-(glycyl)-adenosine-5'-(O-methylphosphate) and below 23 degrees C (15 degrees C to -5 degrees C) for 6.2 mM 2'(3')-O-(glycyl)-P1, P2-diadenosine-5'-pyrophosphate. The absence of a template effect at high temperatures is attributed to the melting of the organized helices. The hydrolysis half-lives at pH 8.0 and -5 degrees C of 2'(3')-O-(glycyl)-adenosine, 2'(3')-O-(glycyl)-adenosine-5'-(O-methylphosphate), 2'(3')-O-(glycyl)-P1, P2-diadenosine-5'-pyrophosphate, and 5'-O-(glycyl)-adenosine in the presence of poly(U) are substantially larger than their half-lives in the absence of poly(U). The condensation of 2'(3')-O-(glycyl)-adenosine yields 5% of 5'-O-(glycyl)-adenosine in the presence of poly(U) compared to 0.7% in the absence of poly(U).
Adenine Nucleotides↗
Radiological aspects of inverted papilloma.
Of 115 proved cases of inverted papilloma, 81 were studied radiographically. The tumor was seen in both early and late stages. Many cases presented as recurrent tumor after multiple surgical procedures. A common radiologic presentation was a unilateral mass in the nasal fossa with opacification of the contiguous maxillary sinus in a moderately advanced tumor stage. However, other radiologic patterns were encountered and it was therefore impossible to categorize any of these findings as specific for inverted papilloma.
Adolescent↗
Radiological evaluation of orbital metastases, with emphasis on computed tomography.
Metastases to the orbit are found in the choroid, retrobulbar soft tissues, or bony orbit. Choroidal metastases result in retinal detachment and are best evaluated with fundoscopy and ultrasound. Retrobulbar metastases can involve both extraconal and intraconal spaces; they appear as masses having a high absorption value and irregular margins on plain CT scans and show slight contrast enhancement. The greater wing of the sphenoid is the most common site of bone metastases. These lesions often have soft-tissue components in both the lateral extraconal space of the orbit and the middle cranial fossa.
Breast Neoplasms↗
Human non-24-hour sleep-wake cycles in an everyday environment.
A sighted college student maintained a sleep-wake cycle longer than 24 hr in his everyday environment for more than half of nearly four years. The range of sleep-wake periods and the amount and regularity of sleep are consistent with those found in time-free environments. Episodes of 24 hr periodicity suggest that social cues or obligations are effective entraining agents. He reported more sleep difficulties while on a 24 hr than a non-24-hr schedule.
Adult↗
Delay of constant light-induced persistent vaginal estrus by 24-hour time cues in rats.
The normal ovarian cycle of female rats is typically replaced by persistent estrus when these animals are housed under constant light. Evidence presented here shows that the maintenance of periodicity in the environment can at least delay (if not prevent) the photic induction of persistent vaginal estrus. Female rats in constant light were exposed to vaginal smearing at random times or at the same time every day. In another experiment, female rats were exposed to either constant bright light, constant dim light, or a 24-hour photic cycle of bright and dim light. The onset of persistent vaginal estrus was delayed in rats exposed to 24-hour time cues even though the light intensities were the same as or greater than those for the aperiodic control groups. The results suggest that the absence of 24-hour time cues in constant light contributes to the induction of persistent estrus.
Animals↗
The formation of dipeptides from amino acids and the 2'(3')-glycyl ester of an adenylate.
The yields of dipeptide obtained from the reaction of 0.2M 2'(3')-O-(glycyl)-adenosine-5'-(O-methylphosphate) and 0.2M amino acid at pH 8.2 ranged from 0.1% to 35.5% for a group of 15 amino acids. The yields of glyser (35.3%), gly-cys (11.8%) and gly-thr (5.4%) were considerably greater than dipeptide yields obtained from any of the other 12 amino acids (less than or equal to 1.7%). Aminolysis of 0.05M 2'(3')-O-(glycyl)-adenosine-5-'-(O-methylphosphate) by 0.4M serine ethyl ester yielded 53% glycylserine diketopiperazine, via N-(glycyl)-serine ethyl ester as a transient intermediate. The prebiotic significance of these reactions is discussed.
Adenosine Monophosphate↗
The formation of peptides from glycine thioesters.
The condensation products obtained from 0.01M S-glycyl-N-acetyl-cysteamine at different pH's were investigated. The highest yields of diketopiperazine (approx. 50%) were observed in phosphate buffers between pH 7.5 and 8.5. The highest yields of diglycine (46%), triglycine (10%) and tetraglycine (2%) were observed in carbonate buffers at pH 9.5. At pH 8.0, over 90% of the glycyl residues of 0.15M S-glycyl-N-acetylcysteamine were incorporated into condensation products, mainly DKP (60--70%). The yields of products from the condensation of S-glycyl-ethanethiol under similar conditions closely resembled those obtained with S-glycyl-N-acetylcysteamine.
Esters↗