Tyrosine-225 is hydrogen-bonded to the 3'-hydroxyl group of pyridoxal 5'-phosphate in the active site of aspartate aminotransferase. Replacement of this residue with phenylalanine (Y225F) results in a shift in the acidic limb of the pKa of the kcat/KAsp vs pH profile from 7.1 (wild-type) to 8.4 (mutant). The change in the kinetic pKa is mirrored by a similar shift in the spectrophotometrically determined pKa of the protonated internal aldimine. Thus, a major role of tyrosine-225 is to provide a hydrogen bond that stabilizes the reactive unprotonated form of the internal aldimine in the neutral pH range. The Km value for L-aspartate and the dissociation constant for alpha-methyl-DL-aspartate are respectively 20- and 37-fold lower in the mutant than in the wild-type enzyme, while the dissociation constant for maleate is much less perturbed. These results are interpreted in terms of competition between the Tyr225 hydroxyl group and the substrate or quasi-substrate amino group for the coenzyme. The value of kcat in Y225F is 450-fold less than the corresponding rate constant in wild type. The increased affinity of the mutant enzyme for substrates, combined with the lack of discrimination against deuterium in the C alpha position of L-aspartate in Y225F-catalyzed transamination [Kirsch, J. F., Toney, M. D., & Goldberg, J. M. (1990) in Protein and Pharmaceutical Engineering (Craik, C. S., Fletterick, R., Matthews, C. R., & Wells, J., Eds.) pp 105-118, Wiley-Liss, New York], suggests that the rate-determining step in the mutant is hydrolysis of the ketimine intermediate rather than C alpha-H abstraction which is partially rate-determining in wild type.

No abstract

No abstract

Eosinophilic cystitis is a rare disease of the bladder, for which there is no clear cause or standard treatment. We report the case of a 61 year old man who presented with irritative voiding symptoms and gross hematuria. Cystoscopy showed diffuse urothelial erythema and a posterior bladder wall ulcer. Bladder biopsy revealed marked eosinophilic cystitis with ulceration. Urine culture grew Candida glabrata . After treatment with oral fluconazole, his voiding symptoms resolved and subsequent bladder biopsy revealed a complete dearth of eosinophils. This is the first case report linking eosinophilic cystitis to Candida glabrata .

Accurate pathologic evaluation is essential for proper diagnosis and treatment of patients with cancer. ASCO and the College of American Pathologists have successfully collaborated over the last 15 years to improve collaboration between clinical oncologists and pathologists and to standardize pathologic assay techniques. Cancer is an increasingly recognized societal burden in low- and middle-income countries. In 2015, ASCO and the College of American Pathologists implemented an initiative to identify countries that could benefit from peer insights by jointly convening an international workshop among members of both organizations and pathologists and clinical oncologists from Haiti, Honduras, Vietnam, and Uganda. Honduras was chosen as a pilot site, and representatives of ASCO, the College of American Pathologists, and the Honduras pathology and clinical oncology communities have identified areas in which collaboration might be productive. Multiple barriers, including high poverty levels, poor cancer awareness educational programs, lack of human resources, and delayed diagnosis and treatment, have resulted in a higher cancer mortality rate in Honduras compared with high/moderate-income countries and are shared by other low-income countries. ASCO and the College of American Pathologists member faculty supported a symposium led by Honduras colleagues for interested Honduran pathologists and oncologists. The Honduran communities are now working to establish national resource-appropriate guidelines for both pathology and clinical oncology. Taken together, these efforts indicate that barriers to meet the needs of the clinical oncologists in a low-income country such as Honduras are challenging but not insurmountable.