Isolation of a large glycopeptide from cartilage procollagen by collagenase digestion and evidence indicating the presence of glucose, galactose and mannose in the peptide.

Digestion of cartilage procollagen, pro-α1(II), with bacterial collagenase followed by fractionation of Sephadex G-150 yielded a large glycopeptide (molecular weight 13,200) which could not be demonstrated in a similarly prepared digest of α1(II) chain. Isotopic studies suggested that this glycopeptide contained, in addition to glucose and galactose, mannose, a sugar that is not found in the authentic α-chain of cartilage. The results imply that in pro-α1(II) there is a glycopeptide region differing from the α1(II) chain in amino acid composition and also in the type of carbohydrates attached.     

Affinity isolation of RNA polymerase II on amanitin-Sepharose

We report here the first case of an affinity isolation of eukaryotic RNA polymerase II. The procedure employs an affinity matrix composed of α-amanitin coupled to Sepharose 4B via a ten atom spacer. RNA polymerase II from either calf thymus or wheat germ binds to the amanitin-Sepharose, as indicated by subsequent elution with sodium dodecylsulfate-containing buffer and analysis by polyacrylamide gel electrophoresis. The specificity of binding is demonstrated by the fact that when the enzyme is preincubated with 1 μg/ml of free α-amanitin, subsequent binding to the amanitin-Sepharose is abolished. Elution methods that should permit the recovery of active enzyme from the column are discussed.     

Dimeric character of fibronectin, a major cell surface-associated glycoprotein

Exposed proteins of cultured chick and human fibroblasts were labeled by lactoperoxidase-catalyzed iodination and analyzed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Extracts from both cell types contained the characteristic, heavily labeled band of fibronectin (molecular weight = 2.2 × 10⁵) when analyzed after reduction with 2-mercaptoethanol. Without prior reduction, however, the 2.2×10⁵ molecular weight band was missing and replaced by labeled bands of 4.4×10⁵ and of very high molecular weight. This finding indicates that fibroblast cell-surface fibronectin, like the fibronectin purified from plasma, is composed of two high molecular weight polypeptides hed together by disulfide bonds, and suggests that the dimer may in addition form disulfide-bonded multimers.     

A gel-electrophoretically homogeneous preparation of cytochrome P-450 from liver microsomes of phenobarbital-pretreated rabbits

Cytochrome P-450 was purified from liver microsomes of phenobarbital-pretreated rabbits to a specific content of 16 to 17 nmoles per mg of protein with a yield of about 10 %. The purified cytochrome yielded only a single protein band on sodium dodecylsulfate-urea-polyacrylamide gel electrophoresis, and an apparent molecular weight of about 45,000 was estimated for the protein. The preparation was free of cytochrome $\text{b}{}_5$, NADH-cytochrome $\text{b}{}_5$ reductase, and NADPH-cytochrome $\text{c}$ reductase activities. Aniline hydroxylase and ethylmorphine N-demethylase activities could be reconstituted upon mixing the purified cytochrome with an NADPH-cytochrome $\text{c}$ reductase preparation (purified by a detergent method) and phosphatidyl choline.     

A porin activity of purified lambda-receptor protein from Escherichia coli in reconstituted vesicle membranes.

The receptor protein for bacteriophage λ was purified to homogeneity from a mutant strain of $\text{Escherichia coli}$ K-12 producing reduced amounts of porin. In the reconstituted vesicle membranes the λ-receptor formed permeability channels that allowed the diffusion of maltose, lactose, sucrose, raffinose, amino acids, and nucleosides, but essentially not of stachyose. The permeability channels made of λ-receptor thus had a relatively low specificity for solute molecules. The active form of the protein seemed to be an oligomer of λ-receptor proteins.     

Calcium-calmodulin dependent phosphorylation of erythrocyte pyruvate kinase

In the red cell incubated with ortho-[32P] phosphate, CaCl₂ and calcium ionophore A 23187, phosphorylation of erythrocyte pyruvate kinase was demonstrated using the double antibody technique and autoradiography. Phosphorylation was inhibited by calmodulin inhibitors, trifluoperazine or ZnCl₂. In the presence of purified erythrocyte calmodulin, CaCl₂ and [γ-³²P] ATP, the partially purified erythrocyte pyruvate kinase containing cytozol protein kinases was phosphorylated. This was also inhibited by trifluoperazine or ZnCl₂. From these results, it was concluded that erythrocyte pyruvate kinase is phosphorylated by a calcium-calmodulin dependent process.