A general pre-steady-state solution to complex kinetic mechanisms

We have developed a general method for solving transient kinetic equations using Laplace transforms. Laplace transforms can be used to transform systems of differential equations that describe pre-steady-state kinetics to systems of linear algebraic equations. The general form of the pre-steady-state solution is (formula; see text) where I(t) is the time dependence of the physically observed property of the system, n is the number of intermediates, lambda i are the observed rate constants (reciprocals of the relaxation times), t is time, and Ii are the amplitude coefficients associated with each observed rate constant. We have written a program in compiled BASIC to run on a personal computer to evaluate Ii and lambda i. The program will evaluate the rate constants and coefficients of a mechanism with eight intermediates and seven relaxation times in 4 s on an 8-MHz PC-XT equipped with a math coprocessor. The most complex mechanism that we have solved, a mechanism containing 20 intermediates and 19 relaxation times, required approximately 5 min. We believe that this method will be useful to evaluate the differences in transient properties of complex biochemical mechanisms.     

Multiple forms of SppI (secreted phosphoprotein, osteopontin) synthesized by normal and transformed rat bone cell populations: regulation by TGF-beta

Metabolic labeling has revealed that rat bone cell populations in culture synthesize several forms of the secreted phosphoprotein, SppI. Most cell populations produced two major [32PO4]-labeled forms that behaved anomolously on SDS-PAGE migrating at 60 kDa and 56 kDa on 10% gels and 55 kDa and 44 kDa on 15% gels. Minor forms of intermediate sizes were also resolved. In normal bone cells the 60 kDa form was predominant and was the only form produced by the clonal bone cell line, RCA 11, whereas the 56 kDa a form predominated in the transformed bone cell line, ROS 17/2.8. In all populations [35S]-methionine-labeling revealed SppIs at approximately 60 kDa but no 56 kDa form. Each form of SppI was specifically cleaved by thrombin which generated fragments of approximately 28 kDa. Transforming growth factor beta 1 increased SppI mRNA levels 3 to 6-fold within 24 h in the normal bone cells, but no increase occurred in the ROS 17/2.8 cells. The elevated expression of SppI was reflected in a selective increase in the synthesis of the [32PO4]-and [35S]-methionine-labeled 60 kDa SppIs.     

Effect of the hinge protein on the heme iron site of cytochrome c1

X-ray absorption spectroscopic (XAS) studies on cytochrome C1 from beef heart mitochondria were conducted to identify the effect of the hinge protein [Kim, C.H., & King, T.E. (1983) J. Biol. Chem. 258, 13543-13551] on the structure of the heme site in cytochrome c1. A comparison of XAS data of highly purified "one-band" and "two-band" cytochrome c1 [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961] demonstrates that the hinge protein exerts a rather pronounced effect on the heme environment of the cytochrome c1: a conformational change occurs within a radius of approximately 5 A from the heme iron in cytochrome c1 when the hinge protein is bound to cytochrome c1. This result may be correlated with the previous observations that the structure and reactivity of cytochrome c1 are affected by the hinge protein [Kim, C.H., & King, T.E. (1987) Biochemistry 26, 1955-1961; Kim, C.H., Balny, C., & King, T.E. (1987) J. Biol. Chem. 262, 8103-8108].     

转化生长因子β

TGFβ广泛存在于动物体多种组织和细胞内,由二条相同的、含112个氨基酸的肽链组成,是细胞的多功能双重调节因子。它对不同组织类型的细胞,可促进生长、分化,也可抑制生长、分化,并直接参与组织修复、胚胎发育等过程,调节细胞外基质形成。     

Water status of drought-resistant and drought-sensitive sorghum treated with ethephon

The effects of ethephon on stomatal resistance, water potential, osmotic potential, turgor potential, and ethylene production were determined on leaves of a drought-resistant (KS 65) and a drought-sensitive (IA 25) genotype of sorghum [Sorghum bicolor (L.) Moench] grown under wellwatered or drought-stressed conditions. With both sufficient and limited water supply, ethephon had no effect on the adaxial, abaxial, or total stomatal resistance of either genotype. For both water treatments, the adaxial stomatal resistance of the drought-sensitive genotype was higher than that of the drought-resistant genotype. Ethephon increased the amount of ethylene produced by the plants under both levels of water. For plants with sufficient water, water potentials of both genotypes were lowered by ethephon. Ethephon had no effect on the water potentials under drought or on the osmotic potentials under either water regime. With drought, the turgor potential of the drought-sensitive genotype, but not that of the drought-resistant, was increased by ethephon.     

Purification of D-beta-hydroxybutyrate dehydrogenase from rat brain

D-beta-Hydroxybutyrate dehydrogenase (BDH), a lipid-requiring enzyme, has been purified to homogeneity from rat brain using a new improved method. The purified rat brain BDH has a subunit molecular mass of 31 kilodaltons on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The apoenzyme, i.e., the enzyme devoid of phospholipid, has no activity, but can be activated by phospholipid to a specific activity of 125 mumol/(min.mg). This is 625-fold greater than the activity in the mitochondrial fraction. The new purification procedure involves chromatography using a quaternary amine Sepharose resin followed by a sulphonate Sepharose resin, and eliminates the need for glass bead adsorption chromatography.     

Sand burial effects on seed germination, seedling emergence and establishment of Panicum virgatum

Studies in the field and in a greenhouse were conducted to examine the effects of sand burial on seed germination, seedling emergence and establishment of Panicum virgatum L. on the foredunes of Lake Erie. Under natural conditions, the seedlings emerged from sand burial depths ranging from 0 to 11 cm, with a mean ± SD of 4.73 ± 1.82 cm. The frequency distribution of the depth of emergence of seedlings in the field was significantly skewed to the right and platykurtic. In the greenhouse, some seedlings emerged from a burial depth of as much as 16 cm. Although percent germination of seeds was not affected by sand burial, the percent emergence and the rate of emergence of seedlings were significantly reduced by excessive sand burial. Seedling mortality was found only among seedlings that emerged from sand burial depths of 10 cm or more. In the field, all the seedlings established in one growing season had originally emerged from sand burial depths of less than 12 cm. Within this burial range, seedlings from shallower burial depths had lower chances of establishment than expected, whereas those from deeper burial depths had higher probabilities of establishment than expected.