A structural comparison of the A and B subunits of Griffonia simplicifolia I isolectins

A structural comparison between the A and B subunits of the five tetrameric Griffonia simplicifolia I isolectins (A4, A3B, A2B2, AB3, B4) was undertaken to determine the extent of homology between the subunits. The first 25 N-terminal amino acids of both A and B subunits were determined following the enzymatic removal of N-terminal pyroglutamate blocking groups with pyroglutamate aminopeptidase. Although 21 amino acids were common to both subunits, there were four unique amino acids in the N-terminal sequence of A and B. Residues 8, 9, 17, and 19 were asparagine, leucine, lysine, and asparagine in subunit A and threonine, phenylalanine, glutamic acid, and serine in subunit B. The last six C-terminal amino acids, released by digestion with carboxypeptidase Y, were the same for both subunits: Arg-(Phe, Val)-Leu-Thr-Ser-COOH. Subunit B, which contains one methionyl residue, was cleaved by cyanogen bromide into two fragments, a large (Mr = 31,000) and a small (Mr = 2700) polypeptide. Failure of the small fragment to undergo manual Edman degradation indicated an N-terminal blocking group, presumably pyroglutamate. Both subunits were digested with trypsin and the tryptic peptides were analyzed using reverse-phase HPLC. Tryptic glycopeptides were identified by labeling the carbohydrate moiety of the A and B subunit using sodium [3H] borohydride. Cysteine-containing tryptic peptides were similarly identified by using [1-14C]iodoacetamide. Approximately 30% of the tryptic peptides were common to both subunits. Thus, although the N- and C-terminal regions of A and B are similar, the subunits each possess unique sequences.     

Biophysical and enzymological studies upon the interaction of trans-cinnamic acid with higher plant microsomal cytochromes P-450.

The interaction of trans-cinnamic acid with the cytochrome P-450 of microsomes derived from washed potato slices has been studied. The washing process increased the specific content of microsomal electron transport components and hence provided a useful material in which to study the interaction. Evidence is presented that the trans-cinnamic acid interacts with the cytochrome P-450, and that this interaction is analogous to "type 1" interactions of other cytochrome P-450 systems. This evidence includes the formation of a "type 1" substrate binding spectrum, an increased rate of reduction of cytochrome P-450 by NADPH in the presence of trans-cinnamic acid, an increased oxygen uptake and NADPH oxidation when trans-cinnamic acid is added to the microsomes in the presence of NADPH, and a close correlation between biophysical parameters of electron transport in the cytochrome P-450 system and enzymological parameters of the trans-cinnamic acid 4-hydroxulation reaction. The investigation has been extended to cytochrome P-450 systems of other tissues and it has been found that the trans-cinnamic acid 4-hydroxylation reaction cannot account for the presence of most of th cytochrome P-450 in several tissues. This suggests that other functions of higher plant cytochrome P-450 chains exist, and that the substrate specificityof the hemoprotein may vary in different plant tissues.     

Influenza virus M2 protein has ion channel activity.

The influenza virus M2 protein was expressed in Xenopus laevis oocytes and shown to have an associated ion channel activity selective for monovalent ions. The anti-influenza virus drug amantadine hydrochloride significantly attenuated the inward current induced by hyperpolarization of oocyte membranes. Mutations in the M2 membrane-spanning domain that confer viral resistance to amantadine produced currents that were resistant to the drug. Analysis of the currents of these altered M2 proteins suggests that the channel pore is formed by the transmembrane domain of the M2 protein. The wild-type M2 channel was found to be regulated by pH. The wild-type M2 ion channel activity is proposed to have a pivotal role in the biology of influenza virus infection.     

Single-dose murine monoclonal antibody ricin A chain immunotoxin in the treatment of metastatic melanoma: a phase I trial.

To determine the maximally tolerated dose of a ricin A chain-conjugated antimelanoma antibody (XomaZyme-Mel), 20 patients with metastatic melanoma were treated with escalating doses of the murine immunotoxin given as single intravenous infusion over 30 minutes. The starting dose was 0.6 mg/kg and was escalated in five groups to a maximum of 1.6 mg/kg. The maximally tolerated dose was 1.25 mg/kg as three of six patients treated at 1.6 mg/kg developed unacceptable toxicity. The dose-limiting toxicity consisted of profound fatigue, myalgias, and arthralgias. These occurred within 4 days and resolved in 7 to 10 days. Other non-dose-limiting toxicities encountered consisted of hypoalbuminemia, weight gain, peripheral edema, mild hypotension, and flu-like syndrome; the severity of these was also dose related. In addition, two allergic reactions occurred, one severe. There was one durable complete response of 12+ months' duration and one brief mixed response lasting 3 months. We conclude that the maximum tolerated single dose of XomaZyme-Mel is 1.25 mg/kg. Phase I studies evaluating 1.25 mg/kg given in multiple doses at 2- to 4-week intervals and phase II studies to determine the response rate of a single 1.25 mg/kg dose are warranted.     

Clinical features and molecular analysis of the α thalassemia/mental retardation syndromes. 1. Cases due to deletions involving chromosome band 16p13.3

We describe eight patients who have alpha thalassemia which cannot be accounted for by the Mendelian inheritance of abnormal alpha globin genes. Apart from the hematologic abnormality, the other universal clinical finding is mild to moderate mental handicap; there is also a broad spectrum of associated dysmorphic features. Initial analysis of the alpha globin gene complex (which maps to chromosome band 16p13.3), demonstrated that the alpha thalassemia results from failure of the patient to inherit an alpha globin allele from one of the parents. Using a combined molecular and cytogenetic approach, we have extended this analysis to show that all of these patients have 16p deletions which are variable in extent but limited to the terminal band 16p13.3; in at least four cases the deletion results from unbalanced chromosome translocation, and hence aneuploidy of a second chromosome is also present. The relatively nonspecific clinical phenotype contrasts with the other currently known microdeletion syndromes; this may reflect ascertainment bias in the recognition of such syndromes. This work represents the first step in the characterization of a new microdeletion syndrome that is probably underdiagnosed at present.