Lactate dehydrogenase isozymes from the woodlouse Porcellio laevis Latreille (Porcellionidae, Isopoda) : physical and chemical properties
Ahmad, K.; Alikhan, M.A.
Indian Journal of Biochemistry and Biophysics 16(5): 278-283
1979
ISSN/ISBN: 0301-1208 PMID: 540933 Document Number: 143741
P. laevis lactate dehydrogenase [LDH] has a MW of 140,000 daltons. It shows maximum activity at 0.3 mg .beta.-NADH and 18.16 .times. 10-2 M pyruvate incubated in 0.1 M phosphate buffer (pH 6.5) at 35-37.degree. C for 3 min. Under these optimal conditions 87% LDH activity is found in the hemolymph and muscles, and 13% in the hepatopancreas and alimentary canal. The enzyme is activated by sodium citrate, sodium oxalate, sodium fluoride, lithium chloride, EDTA and urea. ATP concentrations greater than 0.25 mM inhibit the enzyme. The Hill coefficient for the reaction containing ATP was 2.03, indicating that the enzyme has at least 2 ATP binding sites which interact in a cooperative, allosteric manner. Three isozymes of LDH were extracted from the woodlouse tissue, and their properties are described. The nature of the LDH isozymes is discussed.