Biomedical subjects

N Rhodes

Publications and source records attributed to N Rhodes.

24 records · Page 2Linked to original sources

PubMed1990

STE11 is a protein kinase required for cell-type-specific transcription and signal transduction in yeast.

The STE11 gene of Saccharomyces cerevisiae is one of several genes required for mating between two haploid cell types of this yeast. Its product is required for response to a signal that causes arrest of the mitotic cell cycle in the G1 phase and induction of mating-type-specific genes. The nucleotide sequence of the STE11 gene was determined. The predicted amino acid sequence shows homology to the protein kinase family. We demonstrate that the STE11 product has kinase catalytic activity and that this activity is required for its in vivo functions.

Amino Acid Sequence↗

PubMed1990

Relationship of cranial ultrasonography, visual and auditory evoked responses with neurodevelopmental outcome.

Sixty-two preterm infants were followed up with flash visual evoked responses (VERs), brainstem auditory evoked responses (BAERs) and neurodevelopmental assessments for 18 months after term. Cranial ultrasonography showed that 18 infants developed intraventricular haemorrhage (IVH) during the newborn period and four of six infants with grade III or IV haemorrhage had absent VERs at term. The mean latency of the VER in the infants with IVH was significantly shorter than that of infants without IVH. There was no correlation between the degree of ventricular dilatation at term and the latency of the VER. Six months after term the four infants with previously absent VERs had normal responses, though there was still a significant difference between the latencies of infants with and without IVH. At 12 and 18 months of age these differences had disappeared. BAERs were not significantly different in the infants with and without IVH, and there was no difference in the VERs or BAERs of infants with neurodevelopmental delay and those developing normally. Neither flash VERs nor BAERs provide a good prognostic indicator of future neurodevelopmental disability or outcome.

Brain↗

PubMed1987

Exponential model for a regulatory enzyme. Computer program for the determination of the model constants from initial velocity data.

The paper describes a program (DESCENT) which evaluates the constants of the exponential model for a regulatory enzyme with up to four substrates or up to three substrates and one effector. The program operates by repetitive adjustment of the model constants so as to secure a better fit between the observed and calculated initial velocities of reaction. At each adjustment, all the constants are incremented simultaneously by amounts determined by a steepest descent criterion. The program is tested by artificial data with and without added error and it is shown that good estimates of the constants can be recovered.

Allosteric Regulation↗

PubMed1986

The regulatory properties of yeast pyruvate kinase. Effect of pH.

The kinetics of pyruvate kinase from Saccharomyces cerevisiae were studied at 25 degrees C as a function of the concentrations of the substrates ADP, phosphoenolpyruvate and Mg2+ and the effector H+ in the pH range 5-6.6. The enzyme was activated by 100 mM-K+ and 32 mM-NH4+ throughout. It was found that the data could be described by the exponential model for a regulatory enzyme. On that basis, it was concluded that the binding of H+ is positively interactive and that the protonated enzyme is catalytically inactive. It was also found that H+ interacts positively with phosphoenolpyruvate but negatively with both ADP and Mg2+.

Adenosine Diphosphate↗

PubMed1986

The regulatory properties of yeast pyruvate kinase. Effects of NH4+ and K+ concentrations.

The kinetics of pyruvate kinase from Saccharomyces cerevisiae were studied at 25 degrees C and pH 6.2 as a function of the concentrations of ADP, phosphoenolpyruvate, Mg2+ and either NH4+ or K+. The data were analysed by the exponential model for four substrates, obtained by extension of the model described by Ainsworth, Kinderlerer & Gregory [(1983) Biochem. J. 209, 401-411]. On that basis, it was concluded that NH4+ binding is almost non-interactive but leads to the appearance of positive interaction in the velocity response to increase in its concentration because of positive interactions with phosphoenolpyruvate and Mg2+. The data obtained with K+ lead to the same conclusions and differ only in suggesting that NH4+ is bound more strongly to the enzyme than is K+. Both data sets are used as the basis for a discussion of the substrate interactions of pyruvate kinase and it appears therefrom that the heterotropic interactions accord with what is known of the events that take place at the active site during catalysis. The paper also reports a determination of the dissociation constants for the NH4+ complexes with ADP and phosphoenolpyruvate and an examination of the simultaneous activation of pyruvate kinase by K+ and NH4+ ions.

Adenosine Diphosphate↗

PubMed1986

Calculation of Hill slopes predicted by the four ligand exponential model for a regulatory enzyme.

The Hill slopes predicted by the exponential model for a regulatory enzyme have been calculated by two separate methods, one analytical and the other numerical. Both methods are applicable to enzymes with up to 4 substrates; alternatively, one substrate may be replaced by an effector. The maximum or minimum Hill slope can also be ascertained by an extension of the analytical method.

Enzymes↗