PubMed Health⌕ Search

Biomedical subjects

L Copeland

Publications and source records attributed to L Copeland.

46 records · Page 3Linked to original sources
PubMed1980

Beta-D-mannanases in germinating lucerne (alfalfa) seeds.

Extraction and fractionation of the beta-D-mannanases in germinating lucerne produced four fractions if extracts were stored prior to chromatography. However, when extracts were applied rapidly to DEAE-cellulose, one of the fractions of high molecular weight (separated subsequently by gel chromatography) was not detected, indicating that it was formed after maceration. On storage, the amount of the lower-molecular-weight, unbound fraction from chromatography on DEAE-cellulose did not increase relative to that bound. During germination, the bound and unbound fractions both increased initially and then decreased, with only small changes in the ratio of each. The results suggest that three of the beta-D-mannanase fractions are formed in vivo prior to maceration.

Isoenzymes↗
PubMed1978

Fructokinase (Fraction III) of Pea Seeds.

A second fructokinase (EC 2.7.1.4) was obtained from pea seed (Pisum sativum L. var. Progress No. 9) extracts. The enzyme, termed fructokinase (fraction III), was specific for fructose and had little activity with glucose. With fructose concentrations above 0.25 millimolar, there was strong substrate inhibition at the optimum pH (8.0) and also at pH 6.6. The apparent K(m) values at pH 8.0 for fructose and glucose were 0.06 millimolar and 0.14 millimolar, respectively. The apparent K(m) for Mg adenosine 5'-triphosphate (MgATP) was 0.06 millimolar and excess MgATP was inhibitory. Mg(2+) was essential for activity but the enzyme was inhibited by excess Mg(2+) or ATP. Mg adenosine 5'-pyrophosphate was also inhibitory. Activity was stimulated by the addition of monovalent cations: of those tested K(+), Rb(+), and NH(4) (+) were the most effective. The possible role of fructokinase (fraction III) is discussed.

Journal Article↗
PubMed1977

Fructokinase (Fraction IV) of Pea Seeds.

A fructokinase (EC 2.7.1.4) was obtained from pea (Pisum sativum L.) seeds. This enzyme, termed fructokinase (fraction IV), was specific for fructose as substrate and had little activity with glucose or mannose. Excess fructose inhibited the enzyme at the optimum pH (8.2) but not at pH 6.6. MgATP was inhibitory at pH 6.6. The apparent Michaelis-Menten constants at pH 8.2 were 0.057 mm for fructose and 0.10 mm for MgATP. Mg(2+) ions were essential for activity; Mn(2+) could partially replace Mg(2+). Fructokinase (fraction IV) had a requirement for K(+) ions which could be substantially replaced by Rb(+) or NH(4) (+) but not by Na(+). The enzyme was inhibited by MgADP. The possible significance of fructokinase (fraction IV) in plant carbohydrate metabolism is discussed.

Journal Article↗