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Biomedical subjects

K G Johnson

Publications and source records attributed to K G Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1974

Beta-D-phosphogalactoside galactohydrolase from Streptococcus cremoris HP: purification and enzyme properties.

beta-d-phosphogalactoside galactohydrolase (beta-PGal) was isolated and purified from cell-free extracts of Streptococcus cremoris HP to apparent homogeneity to gel electrophoresis. Using the chromogenic o-nitrophenol-beta-d-galactopyranoside-6-phosphate as substrate, the purified enzyme exhibited a specific activity of 18.71 U/mg of protein and K(m) and V(max) values of 5.88 x 10(-4) M and 23.8 mumol of o-nitrophenol liberated per min per mg of protein, respectively. d-Galactose-6-phosphate was a weak competitive inhibitor of beta-PGal. Activity was relatively heat resistant and was maximal from pH 5.0 to 8.0 and over a temperature range of 45 to 52 C. Dithiothreitol, ethylenediaminetetraacetic acid, and citrate stimulated beta-PGal activity, whereas Mg(2+), Li(1+), and p-hydroxymercuribenzoate were inhibitory. Molecular weight of the enzyme was estimated at 6.76 x 10(4). Amino acid composition was similar to other beta-phosphogalactosidases previously investigated, with the exception that the S. cremoris enzyme contains a small amount of half cystine.

Amino Acids↗
PubMed1973

Sweat storage as a factor influencing sweat discharge in sheep.

1. Sweat output has been measured continuously from four Welsh Mountain sheep exposed on several occasions for periods of 8 hr to air temperatures of 20, 30 and 40 degrees C. At all temperatures sweat was discharged intermittently. Discharges occurred more frequently at high air temperatures and when the animals were shorn, but not at consistently different frequencies in summer and winter.2. At 40 degrees C T(a), sweat discharges were initially large, decreased in size during the first 1-3 hr, and then continued at regular intervals and at an approximately constant size for the remainder of the experiments. Most, and probably all, sweat glands in the skin were active at each discharge.3. The volumes of sweat glands, determined histologically, decreased after prolonged activity in the heat. Comparison of the changes in sweat gland volumes with the amounts of sweat discharged led to conclusions that the decline in sweat output seen on initial exposure to heat was probably due to depletion of secretory fluid from storage within the gland and that the subsequent regular discharge of small amounts of sweat was due to expulsion of newly formed secretion.4. Examination of serial sections of midside skin revealed that in these sheep sweat glands consisted of a superficial non-convoluted duct separated from a large ampulla by a region in which the gland was convoluted. After long periods of sweating, the glands decreased in diameter in both the convoluted and non-convoluted regions but were never found to be empty.5. The pattern of sweat output from sheep during prolonged exposure to heat appears to be determined not only by processes of secretion and intermittent expulsion but also by the amount and rate of depletion of preformed sweat stored in the gland lumen.

Animals↗