Interaction of P--N--P and P--C--P analogs of adenosine triphosphate with heavy meromyosin, myosin, and actomyosin.
Explore the source record for details and available documents.
Actomyosin↗
Biomedical subjects
D Babcock
Publications and source records attributed to D Babcock.
Regulation of sulfate transport in filamentous fungi.
Inorganic sulfate enters the mycelia of Aspergillus nidulans, Penicillium chrysogenum, and Penicillium notatum by a temperature-, energy-, pH-, ionic strength-, and concentration-dependent transport system ("permease"). Transport is unidirectional. In the presence of excess external sulfate, ATP sulfurylase-negative mutants will accumulate inorganic sulfate intracellularly to a level of about 0.04 m. The intracellular sulfate can be retained against a concentration gradient. Retention is not energy-dependent, nor is there any exchange between intracellular (accumulated) and extracellular sulfate. The sulfate permease is under metabolic control. Sulfur starvation of high methionine-grown mycelia results in about a 1000-fold increase in the specific sulfate transport activity at low external sulfate concentrations. l-Methionine is a metabolic repressor of the sulfate permease, while intracellular sulfate and possibly l-cysteine (or a derivative of l-cysteine) are feedback inhibitors. Sulfate transport follows hyperbolic saturation kinetics with a Michaelis constant (Km) value of 6 x 10(-5) to 10(-4)m and a V(max) (for maximally sulfurstarved mycelia) of about 5 micromoles per gram per minute. Refeeding sulfur-starved mycelia with sulfate or cysteine results in about a 10-fold decrease in the V(max) value with no marked change in the Km. Azide and dinitrophenol also reduce the V(max.).
Journal Article↗
Parenteral nutrition for infants: effect of high versus low calcium and phosphorus content.
Calcium (Ca) and phosphorus (P) homeostasis were determined in 18 infants (birth weight, 2,810 +/- 135 g; gestational age, 37.4 +/- 0.5 weeks; mean +/- SEM) who received high or low Ca and P content (Ca, P) parenteral nutrition (PN) with a fixed, low dose of vitamin D (25 IU/dl). Nine infants were randomized into low (standard) Ca, P (20 mg Ca and 15.5 mg P/dl) and nine into high Ca, P (60-80 mg Ca and 46.5-62 mg P/dl) PN, and then were studied for up to 6 weeks. The high Ca, P group had stable serum 1,25 dihydroxyvitamin D [1,25(OH)2D], which consistently remained within the normal range (less than 116 pg/ml). Tubular reabsorption of phosphorus (TRP) also was stable and remained consistently less than 90%. The low Ca, P group had elevated and higher 1,25(OH)2D (p = 0.03) than the high Ca, P group. The mean serum 1,25(OH)2D concentration rose from 32 to 112, 115, and 133 pg/ml over a period of 6 weeks. TRP also was higher (p = 0.02) and remained consistently greater than 90%. There were no significant differences between groups in serum parathyroid hormone, calcitonin, Ca, Mg, P, alkaline phosphatase, vitamin D binding protein, and 25 hydroxyvitamin D concentrations; urine Ca/creatinine and Mg/creatinine ratios, and fractional excretion of sodium (Na). Thus, a "high" Ca (60 mg/dl) and P (46.5 mg/dl) content in PN solutions can result in stable serum 1,25(OH)2D and TRP, presumably reflecting minimal stress to Ca and P homeostatic mechanisms without further increase in urinary Ca excretion.
Calcium↗