Kinji Kakiuchi

Formation of a complex between yeast l-lactate dehydrogenase (cytochrome b2) and cytochrome c: Ultracentrifugal and gel chromatographic analyses

Yeast L-lactate dehydrogenase formed a stable complex with cytochrome c in weakly alkaline solution of low ionic strength. The binding ratio of cytochrome c to the enzyme depended on whether free cytochrome c was present: In the presence of a micromolar concentration of cytochrome c the enzyme formed a complex with about two molecules of cytochrome c, whereas the enzyme was in a 1:1 molecular complex after removal of free cytochrome c. This suggests that the binding of one molecule of cytochrome c changes the affinity of the other binding site on the enzyme for cytochrome c. The enzyme consists of four presumably identical subunits, each containing a binding site for cytochrome c. Thus, present data confirm the concept of negative cooperativity between the subunits of the enzyme molecule in their interaction with cytochrome c.

Sedimentation equilibrium in aqueous solutions of a nonionic detergent

Abstract The micelle molecular weight of polyoxyethylene oetylphenylether with 20 moles of ethylene oxide in aqueous solution has been determined by the sedimentation equilibrium method. The critical micelle concentration is found to be 0.075 g. d1. −1 , in agreement with that from surface tension measurements. The micelle molecular weight obtained is 35,600, which corresponds to the association number, 32.4. The solution is almost ideal and the micelles are homogeneous in size. The equilibrium constant and the standard free energy for the micelle formation have been estimated. From the sedimentation equilibrium data the number-, weight-, and z -average molecular weights have been obtained at given concentrations, and they are compared with those calculated from the equilibrium constant between monomers and micelles.

Spectroscopic behavior of biliprotein from Porphyra tenera upon denaturation with urea and sodium dodecyl sulfate (SDS)

It is well known that the biliprotein accessory photosynthetic pigments phycoerythrin (PE) and phycocyanin (PC) have been extensively studied. Both PE and PC have been shown to be composed of two kinds of subunits, α and β, by numerous previous investigators.

C-phycocyanin from a red alga, Porphyra tenera: subunit structure

Abstract C-phycocyanin (PC) from a red alga, Porphyra tenera was separated into α and β subunits by SDS-polyacrylamide gel electrophoresis and Bio-Rex 70 column chromatography. The absorption and fluorescence maxima of the phycocyanin were 615 and 632 nm, respectively. The amino acid compositions of phycocyanin and its subunits were predominantly acidic amino acids. The molecular weights of phycocyanin and its subunits were determined to be 111 000 (PC), 18 100 (α) and 22 200 (β) by the sedimentation equilibrium method. It was assumed that the phycocyanin forms a trimeric aggregate, the trimer (αβ)3 at pH 7.0.