Transport ATPases in anion and proton transport

Studies in our laboratory have shown that the anion-sensitive Mg-ATPase is located in mitochondria, but not in the plasma membrane of rabbit gastric mucosa, trout gill, rabbit kidney and rat pancreas; whereas in rabbit erythrocyte membrane, it is part of the Ca-Mg activated ATPase system. These findings appear to rule out a function of the anion-sensitive ATPase in the transport of anions and protons across the plasma membrane in these tissues. On the other hand, the K-activated ATPase in a gradient-purified vesicle fraction of pig gastric mucosa mediates proton uptake in exchange for K+ in the presence of ATP, in agreement with earlier findings of other investigators. The enzyme requires a phospholipid environment for its activity. Studies of arginine modification with butanedione in the presence or absence of ATP and its analogues, and of activating cations indicate that the enzyme contains an essential arginine group involved in ATP binding; and that K+ induces a conformational change, which leads to decreased ATP binding and probably coincides with enzyme dephosphorylation. Similar studies of sulfhydryl modification with DTNB indicate that the enzyme contains an essential sulfhydryl group, which does not appear to be directly involved in ATP binding, but rather that ATP binding may induce a conformational change which makes the sulfhydryl group less accessible.

Arginyl residues and anion binding sites in proteins

The functions of a number of amino acid residues in proteins have been studied by chemical modification techniques and much useful information has been obtained. Methods using dicarbonyl compounds for the modification of arginine residues are the most recent to have been developed. Since their introduction about 10 years ago, they have led to the identification of a large number of enzymes and other proteins that contain arginine residues critical to biological function. These reagents are discussed in terms of their chemical reactivity and mechanisms of action and in relation to the unique chemical properties of the guanidinium group. Butanedione, phenylglyoxal and cyclohexanedione are the most commonly employed arginyl reagents, and their relative advantages are examined. A survey of the functional role of arginine residues in enzymes and other proteins is presented in which nearly 100 examples are cited. The prediction that arginine residues would be found to serve a general role as anionic binding sites in protein has obviously been validated. The genetic and physiological implications of the selection of arginine for this important function are discussed.

Studies on the RNA and protein binding sites of the E. coli ribosomal protein L10

We have used modification of specific amino acid residues in the E. coli ribosomal protein L10 as a tool to study its interactions with another ribosomal protein, L7/L12, as well as with ribosomal core particles and with 23S RNA. The ribosome and RNA binding capability of L10 was found to be inhibited by modification of one more of its arginine residues. This treatment does not affect the ability of L10 to bind four molecules of L7/L12 in a L7/L12-L10 complex. Our results support the view that L10's role in promoting the L7/L12-ribosome association is due primarily to its ability to bind to both 23S RNA and L7/L12 simultaneously.

Magnetic microspheres: synthesis of a novel parenteral drug carrier

The synthesis and characterization of a novel parenteral drug carrier capable of area specific localization by magnetic means are described. The carrier consists of human serum albumin microspheres, average of 1 micrometer in diameter, in which a magnetizable material (magnetite) and a prototype drug (doxorubicin) are entrapped. Stabilization of the microsphere matrix by formaldehyde, 2,3-butanedione, and heat conferred equal stability to the matrix but differentially affected the in vitro drug release rate. Release doxorubicin was chemically identical to the starting material.

Determination of arginine in the reactive site of proteinase inhibitors by selective and reversible derivatization of the arginine side chain

Reversible and selective modification of the guanidino group by 1,2-cyclohexanedione or 2,3-butanedione in borate buffer was applied to identify arginine residues in the reactive sites of proteinase inhibitors. The ability of the method to distinguish between arginine and lysine residues was examined. Trypsin inhibitors with arginine at the reactive site were almost completely inactivated within 2 h, e.g. the low-molecular weight inhibitors from soybeans (Kunitz), peanuts and porcine seminal plasma. Inhibitors of the lysine-type were not inactivated by 1,2-cyclohexanedione/borate, e.g. the bovine trypsin/kallikrein inhibitor, the trypsin inhibitors from cow colostrum, porcine pancreas, or snail epidermis (isoinhibitor K from Helix pomatia), and the human alpha1-proteinase inhibitor (alpha1-antitrypsin). However, 2,3-butanedione/borate does not show this high specificity. The method was applied to four high-molecular weight proteinase inhibitors from the albumin gland of the snail (Helix pomatia). All four inhibitors were subject to inactivation by the reagent, indicating an arginine residue at the reactive site. Evidence is given by NMR, UV, and titration data that a complex is formed from 1,2-cyclohexanedione and borate. Due to this complex formation, the amount of free carbonyl component is drastically decreased. Since 1,2-cyclohexanedione without borate lacks the high specificity for arginine residues, the borate complex of the reagent is presumed to be responsible for the high specificity. The new procedure for identification of reactive sites is based on a reversible modification of the guanidium group of the arginine residues.

A direct method for the estimation of ornithine carbamoyltransferase activity in serum

Ornithine carbamoyltransferase (EC 2.1.3.3) activity was estimated by determining the amount of citrulline produced. The citrulline was colorimetrically measured by using a diacetylmonoxime-thiosemicarbazide reaction without deproteinization. The color complex which had the maximum absorbance at 515 nm was stable at room temperature in daylight for at least several hours. The proposed method was superior to other methods already reported in sensitivity, stability and simplicity.

Aroma values--a useful concept?

Rapidly increasing knowledge about the high complexity of food aromas requires selection or ranking procedures as to the importance of the particular components for flavour impression. For this purpose the concept of aroma values has been discussed which calculates quantitative data in connection with aroma effectiveness of the compounds. The simplification of the concept with respect to the practical application, however, can change the natural system and lead to erroneous conclusions. There are not only interactions between aroma substances of sensoricphysiological character which may not be ignored. Physical conditions like lipid content, distribution of aroma compounds between aqueous and lipid phase or the sorption of volatile substances to the polymer nutrients in foodstuffs are of influence, too.

New Colorimetric reaction for end-point, continuous-flow, and kinetic measurement of urea

A reaction of urea, o-phthalaldehyde and N-(1-naphthyl)ethylenediamine is described for measurement of urea by manual, continuous-flow, and kinetic methods. The continuous-flow system requires 25 mu-l of sample; 40 samples can be analyzed per hour. The kinetic method requires no enzymes, has no lag phase, and has good sensitivity. A major advantage of the reaction is that it occurs at a temperature of 37 degrees C or lower. The results obtained by all three methods agree well with those for a continuous-flow procedure in which diacetyl is a reagent.

The reaction of chymotrypsin with 2,3-butanedione trimer;

A method for the preparation of the trimer of 2,3-butanedione has been developed; The reaction of this trimer with chymotrypsin A alpha was examined in the presence or absence of light. Under conditions of exclusion of light, modification of one to two arginine residues and of a similar number of lysine residues could be achieved without any loss of enzymatic activity. The trimer facilitated a rapid photoinactivation of the enzyme with little or no modification of the above amino acid residues. Such photoinactivation was not found to react with proflavine and diiosopropylfluorophosphate to an extent greater than that expected on the basis of residual activity presentmproflavine protected the enzyme from the trimer promoted photoinactivation.