Quantitative relationships between the measurable transport resistances of membrane carriers: theory and experiment

A theoretical analysis is made of the possible quantitative relationships between the transport resistances that characterise membrane carrier systems. It is shown that there exist only five possible patterns in which to rank the four transport resistances. Symbolising these as A, B, C and D, the five possible patterns are (i) A = B = C = D; (ii) A = B much greater than C, D; (iii) A = B much greater than C = D; (iv) A = B = 2C = 2D; (v) A = 2B = 2C much greater than D. A survey of the available experimental data shows that pattern (ii) is the most prevalent, pattern (v) is often found and pattern (iii) has been identified. None of the ten transport systems so far analysed experimentally failed to fit one of the predicted patterns.     

S-oxalylglutathione is a substrate for gamma-glutamyltransferase (GGT). Implications for the role of GGT in cell proliferation

With glycylglycine or water as acceptor, bovine kidney gamma-glutamyltransferase catalyzes reactions of the known mammalian metabolite, S-oxalylglutathione, at rates comparable to those of L-gamma-glutamyl-p-nitroanilide, a known good substrate. N-Oxalyl-cysteinylglycine is the eventual product of the former reaction. Since oxalyl thiolesters are implicated as important cell proliferation inhibitors, it is proposed that this reaction plays a major role in controlling cell proliferation.     

Absorption of light in photoreceptors: Effect of waveguiding property

The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies     

Widespread occurrence of AP in amyloidotic tissues. An immunohistochemical observation

Plasma (P)-component of amyloid (AP or SAP), while not an integral part of the amyloid fibril, has been considered to be intimately associated with virtually every different type of amyloid. In the present study, we evaluated the distribution of AP in the organs frequently involved in two forms of human systemic amyloidosis (AA and AF) and in mouse AA amyloidosis, by use of immunohistochemistry with anti-AP. Although the amyloid deposits generally showed moderate reactions with anti-AP, they were not always clearly distinguished from the surrounding non-amyloid tissue elements which often stained as well. The basement membrane often showed even stronger reaction to anti-AP than the adjacent amyloid deposits, and liver sections demonstrated such a high overall reaction to anti-AP that the anti-AP reaction on the amyloid deposits was often obscurred. The present results suggest that the binding between AP and the amyloid fibril may not be monospecific, that AP by this technique occurs rather widely throughout the body, and therefore that anti-AP may not be considered as specific a marker for amyloid deposits in immunohistochemical and perhaps other studies as well.     

Effect of temperature on growth of guanidine-resistant mutants of poliovirus

Guanidine-resistant (gr) mutants of poliovirus were previously categorized into four groups by electrophoretic properties and peptide maps of nonstructural virus protein 2C. Growth of mutants in the presence of guanidine depends upon temperature of incubation. The four groups of gr variants respond differently to temperature when guanidine is included in the culture medium. The data suggest clustering of gr mutations at several sites in the guanidine locus.     

Solid-phase synthesis of polymyxin B1 and analogues via a safety-catch approach.

As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.     

S100 alpha, CAPL, and CACY: molecular cloning and expression analysis of three calcium-binding proteins from human heart.

Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues.     

Cell-free processing and segregation of insulin precursors

The biosynthesis, segregation, and processing of preproinsulin (116 amino acids) was investigated to determine the mechanism(s) by which it is translocated across the endoplasmic reticulum membrane. Islet mRNA was translated in the wheat germ cell-free system, and at various times during preproinsulin synthesis, puromycin was added, followed by addition of microsomal membranes. Neither processing of preproinsulin nor translocation of proinsulin into microsomal membranes occurred in the presence of puromycin. Synchronization of preproinsulin translation by addition of 7-methylguanosine 5'-phosphate enabled the timing of preproinsulin synthesis and proinsulin (91 amino acids) segregation into microsomal membranes to be determined. Membrane binding occurs when about 60 amino acids have been polymerized, i.e. prior to the completion of the polypeptide chain. The binding of signal recognition particle to the nascent signal is demonstrated to be an absolute requirement for translocation and processing of preproinsulin. The results indicate that segregation and processing of preproinsulin are co-translational events; no evidence for a post-translational mechanism was found. Furthermore, this work, together with similar studies, suggests that presecretory polypeptides must be synthesized as part of a precursor with a minimum size of 60-80 amino acids in order to effect membrane binding and translocation of the polypeptide chain within the intracisternal space of the endoplasmic reticulum.