Isoelectric focusing and study of ribosomal proteins and lactate dehydrogenase

Investigation of the interaction of pig muscle lactate dehydrogenase with acidic phospholipids at low pH

Interaction of pig muscle lactate dehydrogenase (LDH) with acidic phospholipids is strongly dependent on pH and is most efficient at pH values<6.5. The interaction is ionic strength sensitive and is not observed when bilayer structures are disrupted by detergents. Bilayers made of phosphatidylcholine (PC) do not bind the enzyme. The LDH interaction with mixed composition bilayers phosphatidylserine/phosphatidylcholine (PS/PC) and cardiolipin/phosphatidylcholine (CL/PC) leads to dramatic changes in the specific activity of the enzyme above a threshold of acidic phospholipid concentration likely when a necessary surface charge density is achieved. The threshold is dependent on the kind of phospholipid. Cardiolipin (CL) is much more effective compared to phosphatidylserine, which is explained as an effect of availability of both phosphate groups in a CL molecule for interaction with the enzyme. A requirement of more than one binding point on the enzyme molecule for the modification of the specific activity is postulated and discussed. Changes in CD spectra induced by the presence of CL and PS vesicles evidence modification of the conformational state of the protein molecules. In vivo qualitative as well as quantitative phospholipid composition of membrane binding sites for LDH molecules would be crucial for the yield of the binding and its consequences for the enzyme activity in the conditions of lowered pH.

Preliminary characterization of ribosomes of Entamoeba invadens

The ribosomes of Entamoeba invadens trophozoites have sedimentation coefficients of 77, 53 and 36 S. Most of the ribosomal proteins are basic and their one- and two-dimensional electrophoretic patterns differ from the corresponding patterns of Escherichia coli and Saccharomyces cerevisiae. Two dozen bands were observed in the 10 000 to 100 000 molecular weight range following sodium dodecylsulfate-gel electrophoresis of amoebal ribosomal proteins. Long, thin pronase-sensitive structures were seen in electron micrographs of E. invadens ribosomal preparations.

Ribonuclease of Entamoeba invadens

Two bands of RNAase activity were observed on gel electrophoresis of fractions obtained during partial purification of the RNAase of Entamoeba invadens. The faster migrating band which was responsible for most of the RNAase activity was isolated by gel electrophoresis. A pI of 5.5 was determined for this RNAase activity and estimates of its molecular weight and sedimentation coefficient gave values of about 25 000 and approximately 2.8 S. It exhibited maximum activity around pH 6, and digestion of RNA showed a pattern expected of an endoribonuclease.

The thin-layer isoelectric focusing of lactate dehydrogenase isoenzymes in rabbit lens parts and in intraocular tissues

Lactate dehydrogenase (LDH) isoenzymes of rabbit lens and other intraocular tissues are separated by thin-layer isoelectric focusing and localized as discrete groups of multiple bands with defined isoelectric points after staining by the tetrazolium method. In the rabbit lens parts, the predominant isoenzymes are LDH-4 and LDH-5. The bands show microheterogeneity, are composed of 2-4 subcomponents, and the pattern shows a distribution of the liver type. The activity of the LDH-4 decreases and that of LDH-5 increases in an order given by the equator, anterior and posterior cortex, and nucleus. LDH-3 remains almost constant in all lens parts. LDH-4 is composed of two subcomponents, one of which, the most cathodic with higher isoelectric point, is almost absent in the lens nucleus. Of the LDH localized in the rabbit intraocular tissues, only the retina shows a pattern of five isoenzymes also of the liver type. In all intraocular tissues LDH-3, -4, and -5 are very prominent, show also microheterogeneity of their isoenzyme bands, and are each composed of 4-6 subcomponents. LDH-1 and -2 show only one isofocused component. Species specificity is shown of the LDH isoenzymes in the rabbit, mouse, dog, and calf lens.

Gel isoelectric focusing of mouse lactate dehydrogenase: heterogeneity of the isoenzymes A4 and X4

LDH of mouse organs (including testis) was investigated by isoelectric focusing in polyacrylamide gels. The number of LDH bands in this pattern considerably exceeds the five (six in testis) of the standard electrophoretic pattern. An attempt was made to identify these bands as tetrameric isoenzymes formed by random association of different subunits. This included isoelectric focusing of purified LDH A, B, and X, two-dimensional separation of LDH, urea treatment of LDH, staining with specific substrates, and comparison of different organs. Further experiments were performed to exclude artifacts possibly produced by the isoelectric focusing technique. Different strains of mice were also investigated. The results demonstrate that in addition to the common five LDH bands (A4-B4) one set of five bands is formed by LDH A (A41-A42) and another one by LDH X (X 41-X42). Moreover, an unusual band was found which has a lower molecular weight and no affinity to the other isoenzymes. The data suggest that the heterogeneity of the LDH pattern revealed by isoelectric focusing arises from post-transcriptional events rather than from a number of additional genes.

Protein mapping by combined isoelectric focusing and electrophoresis of mouse tissues. A novel approach to testing for induced point mutations in mammals

The protein-mapping method which combines isoelectric focusing in acrylamide gel and gel electrophoresis was previously used mainly for the separation of plant proteins and human serum proteins. We investigated with this technique soluble proteins of mouse tissues (whole embryos, the liver of fetal and adult mice, kidneys) and the proteins of mouse serum. The technique was tested under a number of different conditions to find those best for our purpose; they may represent some general improvements in the method. The protein patterns show high resolution and excellent reproducibility. About 275 spots were found for fetal liver, about 230 for whole embryos (day 14 p.c.) and about 100 for serum. The fact that a high number of protein spots can be evaluated by a single and comparatively simple experiment suggests that this method may be useful as an assay system for induced point mutations. The protein patterns demonstrated are compared and discgs of dominant lethal examinations after acute and subacute application of these three substances.

The preparation of crystalline human L-lactate--nicotinamide--adenine dinucleotide oxidoreductase isoenzyme 1 involvoing preparative polyacrylamide-gel electrophoresis

A method is presented for the preparation of human heart lactate dehydrogenase (l-lactate-NAD(+) oxidoreductase; EC 1.1.1.27) isoenzyme 1; this involves the use of polyacrylamide-gel electrophoresis as a preparative step. The yield was about 10% with a final specific activity of 220 units/mg of protein, one unit being defined as the amount of enzyme catalysing the oxidation of 1mumol of NADH/min at 25 degrees C, in the presence of 0.33mm-pyruvate. The crystalline preparation contained less than 2% of the other isoenzymes, was homogeneous in the ultracentrifuge and showed only a trace of protein contamination on polyacrylamide-gel electrophoresis. Some properties of the crystalline isoenzyme are reported; E(1%) (1cm)=13.2 at 280nm, s(0) (20,w)=7.43S, pI=4.6, and the apparent K(m) for pyruvate=1.02x10(-4)m. The human isoenzyme and the isoenzyme from pig heart differ with respect to amino acid composition, electrophoretic mobility and solubility. It is possible that these differences do not involve the active site, or sites, but are due to changes in amino acid residues elsewhere in the molecule. The importance of purified human LDH-1 isoenzyme with regard to enzyme radioimmunoassay is emphasized.