Biomedical subjects

H S Goodman

Publications and source records attributed to H S Goodman.

30 records · Page 2Linked to original sources

PubMed1991

The tyrosine-225 to phenylalanine mutation of Escherichia coli aspartate aminotransferase results in an alkaline transition in the spectrophotometric and kinetic pKa values and reduced values of both kcat and Km.

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.

Aspartate Aminotransferases↗

PubMed1990

Dental health personnel planning: a review of the literature.

Dental personnel planning is important in formulating policy in dental education, dental public health programs, and dental care delivery systems. The purpose of this literature review is to illustrate the use of dentist-to-population ratios, need-based models, and demand-based models in the determination of appropriate supply of dental personnel. A historical perspective is provided that demonstrates how political manipulation and subjectivity have characterized the use of these models by organized dentistry, the federal government, and others. The lack of pertinent data and the inability to predict economic, social, political, and epidemiologic trends weaken the applicability of each model in determining future personnel levels. Considering the long-term consequences of the use of each model in personnel planning, caution is urged in using any of the presently available models.

Dental Health Services↗

PubMed1990

Transcriptional analysis of the mouse beta-casein gene.

These studies were designed to further elucidate the relative contributions of transcriptional and posttranscriptional mechanisms involved in beta-casein gene regulation in the mammary epithelial cell line designated COMMA-D and a clonal subline desginated HC-11. Primary transcripts were mapped under various hormonal and substratum conditions using the technique of nuclear run-on transcription and single stranded sense and antisense probes spanning the beta-casein gene. In the presence of insulin alone very little sense transcription is detectable, but antisense transcription is observed, which originates at least 150 basepairs upstream of the normal start site of transcription and is present regardless of hormonal, cell substratum, cell type, or gene activity. Antisense transcription is also detectable in the 3' end of the gene. Insulin, glucocorticoids, and PRL are all necessary for a maximal increase in transcription. A 2- to 4-fold increase in transcriptional activity is observed in the presence of insulin and PRL compared to insulin alone, and this is accompanied by a 125-fold increase in the level of beta-casein mRNA. All three hormones act synergistically to induce a 10-fold increase in transcriptional activity, but the transcriptional increase across the gene is not equimolar. The 5' half of the gene is transcribed at a level that is 2- to 10-fold lower than that of the 3' half of the gene. These studies reveal a significant transcriptional component to beta-casein gene regulation which was not heretofore detected using double stranded cDNA probes representative of only the 3' half of the gene.

Animals↗

PubMed1990