Horst Frunder

Effect of calmodulin, Ca2+ and Mg2+ on the (Ca2+ + Mg2+)-ATPase of erythrocyte membranes

Abstract Calmodulin-depleted isotonic erythrocyte ghosts contain 200 ng residual calmodulin/mg protein which is not removed by extensive washings at pCa 2+ > 7. Specific activity and Ca 2+ -affinity of the (Ca 2+ + Mg 2+ )ATPase increase at increasing calmodulin, with K 0.5 Ca of 0.38 μM at calmodulin concentrations corresponding to that in erythrocytes. High Ca 2+ concentrations inhibit the enzyme. Specific activity and Ca 2+ -affinity of the enzyme decrease at increasing Mg 2+ concentrations. The Ca 2+ − Mg 2+ antagonism is likewise observed at inhibitory Ca 2+ concentrations.

Transformation of (Ca2+ + Mg2+)ATPase of calmodulin-depleted erythrocyte membranes into a high Ca2+-affinity form by Ca2+

Abstract Specific activity and Ca2+-affinity of (Ca2++Mg2+)ATPase of calmodulin-depleted ghosts progressively increase during preincubation with 0.1–2 mM Ca2+. Concomitantly, the increment in ATPase activity caused by calmodulin and the binding of calmodulin to ghosts decrease. The effects of calcium ions are abolished by the addition of calmodulin. ATP protects the enzyme from a Ca2+-dependent decrease of the maximum activity but does not seem to influence the Ca2+-dependent transformation of the low Ca2+-affinity enzyme into a high Ca2+-affinity form.

Bildung und struktur des ascorbatradikals

Abstract The formation and structure of the monoradical of ascorbic acid is described. The 2-monomethyl ether of ascorbic acid stimulates the oxidation of NADH in liver microsomes in the same way as free ascorbic acid. The 3-monomethyl ether and 2,3-dimethyl ether of ascorbic acid do not have this stimulating effect. Subsequently the radical is formed by splitting off a hydrogen atom or electron from the OH-group at the C-3 of ascorbic acid. These experimental results are supported by a calculation of the π -electron density of ascorbic acid, its monoanion acid, its monoanion and its radical on the basis of the extended Huckel molecular orbital method.

Relation between Ca2+-ATPase and endogenous calmodulin of human erythrocyte membranes.

Short incubation of erythrocyte membranes with oleic acid releases Ca2+-independently bound endogenous calmodulin together with a minor fraction of membrane-associated proteins without destruction of the membranes. The released endogenous calmodulin is similar if not identical to cytosolic calmodulin reversibly bound to ghosts in a Ca2+-dependent manner. The release of endogenous calmodulin proceeds without affecting the activity of Ca2+-ATPase when ghosts are incubated with oleic acid in the presence of Ca2+ plus ATP and thereafter freed from oleic acid by washings with serum albumin. Kinetic parameters of Ca2+-ATPase of ghosts with and without endogenous calmodulin are identical as are amounts of exogenous calmodulin bound to these ghosts. Thus, endogenous calmodulin does not function as an essential part of Ca2+-ATPase.

Active participation of medical students in biochemical education: Problems and solutions

Responses Survey of s tudent opinion revealed that the s tudents perceived the exercises as clearly illustrative of the relevance of biochemistry to clinical work. They felt the exercises should be used in class, not merely for self-study. One exercise every two weeks during a thirteen-week course was not considered excessive; many students indicated that the number should be increased. The exercises were also used with a group of medical s tudents about to enter their fourth year of training. These relatively advanced students were extremely enthusiastic, frequently embarking upon lengthy discussions of specific points, drawing upon information acquired in a variety of preclinical and clinical courses. The basic science-oriented faculty was initially somewhat uneasy with clinically-oriented exercises. Instructor s guides were therefore developed which contain explanations of clinical terms and peripheral details, suggestions for further discussion of related issues, and literature references to key facts and important background. These guides, along with practice in using the exercises, have dispelled all hesitation. The exercises have now been in use four yours, are well accepted by the faculty, and continue to enjoy uniformly enthusiastic student response.