Characterization of glucokinase mutations associated with maturity-onset diabetes of the young type 2 (MODY-2): different glucokinase defects lead to a common phenotype.

Glucokinase (GK) is expressed in the pancreatic beta-cells and liver, and plays a key role in the regulation of glucose homeostasis. The enzymatic activity and thermal stability of wild-type (WT) GK and several mutant forms associated with maturity-onset diabetes of the young type 2 (MODY-2) were determined by a steady-state kinetic analysis of the purified expressed proteins. The eight MODY-2 mutations studied were Ala53Ser, Val367Met, Gly80Ala, Thr168Pro, Arg36Trp, Thr209Met, Cys213Arg, and Val226Met. These missense mutations were shown to have variable effects on GK kinetic activity. The Gly80Ala and Thr168Pro mutations resulted in a large decrease in Vmax and a complete loss of the cooperative behavior associated with glucose binding. In addition, the Gly80Ala mutation resulted in a sixfold increase in the half-saturating substrate concentration (S0.5) for ATP, and Thr168Pro resulted in eight- and sixfold increases in the S0.5 values for ATP and glucose, respectively. The Thr209Met and Val226Met mutations exhibited three- and fivefold increases, respectively, in the S0.5 for ATP, whereas the Cys213Arg mutation resulted in a fivefold increase in the S0.5 for glucose. These mutations also led to a small yet significant reduction in Vmax. Of all the mutations studied, only the Cys213Arg mutation had reduced enzymatic activity and decreased thermal stability. Two mutants, Ala53Ser and Val367Met, showed kinetic and thermal stability properties similar to those of WT. These mutants had increased sensitivities to the known negative effectors of GK activity, palmitoyl-CoA, and GK regulatory protein. Taken together, these results illustrate that the MODY-2 phenotype may be linked not only to kinetic alterations but also to the regulation of GK activity.

Conjugated linoleic acid content of milk from cows fed different diets.

Conjugated linoleic acid in milk was determined from cows fed different diets. In Experiment 1, cows were fed either normal or high oil corn and corn silage. Conjugated linoleic acid was 3.8 and 3.9 mg/g of milk fatty acids in normal and high oil treatments, respectively. In Experiment 2, cows consumed one-third, two-thirds, or their entire feed from a permanent pasture. Alfalfa hay and concentrates supplied the balance of feed for the one-third and two-third pasture treatments. Conjugated linoleic acid was 8.9, 14.3, and 22.1 mg/g of milk fatty acids in the one-third, two-third, and all pasture treatments, respectively. Cows grazing pasture and receiving no supplemental feed had 500% more conjugated linoleic acid in milk fat than cows fed typical dairy diets (Experiment 1). In Experiment 3, cows were fed either a control diet containing 55% alfalfa silage and 45% grain, or similar diets supplemented with 3% fish meal, or 250 g of monensin/cow/per day, or fish meal and monensin together. Conjugated linoleic acid was 5.3, 8.6, 6.8, and 8.9 mg/g of milk fatty acids in the control, fish meal, monensin, and fish meal plus monensin treatments, respectively. In Experiment 4, cows were fed either finely chopped alfalfa hay (Treatment 1), or coarsely chopped alfalfa hay (Treatment 2) in a 50% forage and 50% grain diet, or 66.6% grass hay and 33.4% grain (Treatment 3), or 98.2% grass hay (Treatment 4). Conjugated linoleic acid was 7.3, 8.3, 9.0, and 7.9 mg/g of milk fatty acids in treatments 1 through 4, respectively.

Relationship of serum guanase levels with economic characters in Zebu purebred and temperate x Zebu crossbred dairy cattle.

Serum guanase levels of Indian Zebu (Hariana) cattle and its crosses with different exotic levels of temperate breeds of dairy cattle were estimated in 527 animals, and their associations with economic characters were determined. The overall mean value of serum guanase level was 13.46 +/- 0.45 IU/ml of serum. An inverse relationship between the concentration of the enzyme and the frequency of cattle falling within a definite range was observed, as over 75% of the animals possessed 1 to 20 IU/ml of serum guanase. An analysis of variance revealed significant differences (P less than 0.01) in enzyme levels among different genetic groups under study. Hariana (Zebu) purebreds had significantly higher enzyme levels (19.60 +/- 1.85) than any of the crossbred groups, whose enzyme levels ranged from 8.99 +/- 1.41 in Red Dane F1 half-breds to 14.30 +/- 1.11 in Brown Swiss F1 half-breds. The correlation and regression coefficients were significantly positive for reproductive traits such as age at first service and age at first calving, and significantly negative for production traits such as lactation yield and lactation length. These results suggest that selection of dairy cattle based on low serum guanase levels might result in correlated improvements in dairy cattle productivity.